EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3

[EEVblog]

Dave.

[chrome]

I sort of like the idea of the decade LED's but I wonder how hard it will be to read depending on how small the LED's are and how bright they will be

I was wondering why you didn't try using individual LED's to make 7-segment displays, although that would require a bit more space and I'm also not sure about readability.

[EEVblog]

I was wondering why you didn't try using individual LED's to make 7-segment displays

If you do it using the 7 seg driver approach then it's potentially 7-8 times the current.
Other arrangements can drop that current, but it's messy, and the requirement to light up more leds over a longer mux time drops the brightness.
And yes, the readability isn't as great. The best way would probably be more expensive rectangular leds and/or reverse mounting with slots perhaps.

Dave.

[free_electron]

Bweuaark. Readability : zero...
There is a reason no testequipment has used such an approach.
If i look at a powersupply i want to be able to see in one glance what the settings are. Not having to 'decode' it in my head.
Especially with the shifting location of the dot between volts and current. There should be at least an indication if we are in volts or amps mode.
And you can never see both at the same time...

Why not use a dumb 7 segment lcd display. There's cheap 8 diigits out there. You dont need a display controller. You can scan them from the cpu. 8 digit lines and 8 segment lines ( dot is also a segment ) and you can see both volts and current.

Cheap for the sake of cheap is not a good way. It's got to remain usable.

[T4P]

It actually is a brilliant idea for the sake of being cheap,
being vertical and not horizontal which is what dave did is just brilliant

[notsob]

elegant solution dave, but if someone gave me a display like that to read when i was testing, I would probably toss it.

[david77]

...
There is a reason no testequipment has used such an approach.
...

Not quite true. I think HP did something like that way back in the 1940ies or 50ies, even before Nixie tubes became common.
I agree on the rest of your post.

[Uncle Vernon]

It has some merit. Given the likely use of the thing. I don't see too many times something like this would be used without a meter (or three) close by, so a quick and dirty display may be sufficient. Would I buy it? Probably not! But then I am not in the market for an every cent counts display.

An efficient isolated ultra portable USB supply selectively delivering the common 5V 3V3 etc would probably better suit the most common needs even if it lost much of it's nerd appeal.

[EEVblog]

Bweuaark. Readability : zero...
There is a reason no testequipment has used such an approach.
If i look at a powersupply i want to be able to see in one glance what the settings are. Not having to 'decode' it in my head.
Especially with the shifting location of the dot between volts and current. There should be at least an indication if we are in volts or amps mode.
And you can never see both at the same time...

Sorry, forgot to mention that, it normally displays volts, with amps only when you press a button. Same with a single 3/4 digit LCD or LED solution.

Dave.

[Psi]

Might pay to check if, and what price, Digikey can get these things for (they don't list them but have other liteon products)
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2005497_-1

They're lite-on brand so good quality, 0.7inch so small enough, and the red ones i played with were very efficient, 0.6mA and i could see them fine sitting at my bench.  At $0.49 each in 1000 qty they're not expensive either.  Two of them together would give 14 pixel wide, enough for four 3bit x 5bit characters.  I/O wise, if you parallel the 7 columns you'd need 7 +5 +5 = 17 I/O

But i've not seen them for sale at many stores, so i'm not sure if they were a special run that Jamaco did or just a non-stocked product (hence needing to check their availability).

[free_electron]

Sorry, forgot to mention that, it normally displays volts, with amps only when you press a button. Same with a single 3/4 digit LCD or LED solution.

Dave.

 i woud make it display current by default.. when powering up an 'unknown' that's what you typically anxiously keep an eye on ...

if you go for a 31/2 digit passive lcd there are versions that come with V and A symbols sou you could show what is going on.
what happened to the rotary encoder ? gone ?

hammond has translucent enclosures... displays will sine straight through them.

i would have gone with a 2x8 alpha display with led backlight. 5mA for the backlight and plenty of displat real estate to show both set voltage and current and real voltage and current.

something like the DOGM modules ( mouser )

[EEVblog]

i woud make it display current by default.. when powering up an 'unknown' that's what you typically anxiously keep an eye on ...

if you go for a 31/2 digit passive lcd there are versions that come with V and A symbols sou you could show what is going on.
what happened to the rotary encoder ? gone ?

hammond has translucent enclosures... displays will sine straight through them.

i would have gone with a 2x8 alpha display with led backlight. 5mA for the backlight and plenty of displat real estate to show both set voltage and current and real voltage and current.

something like the DOGM modules ( mouser )

I've used those before, I like them, but not that cheap.
Two 3-4 digit 7-segment LCD displays like shown would be cheaper, and easier to read than dot matrix. But harder to drive of course.

Dave.

[MikeK]

I was wondering why you didn't try using individual LED's to make 7-segment displays

If you do it using the 7 seg driver approach then it's potentially 7-8 times the current.

There's no reason to light all of the necessary segments of the digit at the same time, though.  Segments can be multiplexed just as the digits are, which brings current back down to that of a single segment.

[Psi]

You don't get something for nothing. If you have 64 segments and only 1 on at a time you have to put quite a lot of current into the one segment to get the brightness back up. High efficiency leds lose their efficiency at high current.

There's only so far you can trick the human eye before it starts to notice the brightness dip 

[firewalker]

I was wondering why you didn't try using individual LED's to make 7-segment displays

If you do it using the 7 seg driver approach then it's potentially 7-8 times the current.

There's no reason to light all of the necessary segments of the digit at the same time, though.  Segments can be multiplexed just as the digits are, which brings current back down to that of a single segment.

This means larger pin count for the mcu. So the price will go up.  Also there will be a 25xDelay_Time_for_Adequate_Brightness.

Alexander.

[Stephen Hill]

I like the ingenuity of the solution but like others I don't think it's very user friendly. How many devices have you ever owned or used that have this type of display?

I'd personally pay the extra for two 4 Digit LED display.

I work around if you wanted to get close to the 500mA current would be to have a switch to toggle the displays on and off, letting you measure the current with a multimeter. You could also add a two pin header with a removable jumper to measure the current from.

Cheers
Ste

[EEVblog]

There's no reason to light all of the necessary segments of the digit at the same time, though.  Segments can be multiplexed just as the digits are, which brings current back down to that of a single segment.

Not really. As I said after that line, and as PSI said, the brightness will drop with the increase in mux number. You can't get something for nothing.

Dave.

[Psi]

hm.. yeah, i like the circle idea. It is easier to read as people are more use to reading a clock.

Another idea is side mounted LEDs that illuminate a silkscreen number (maybe inverted, white box, text=nosilkscreen to reflect the light better).
That would make it instantly obvious what the voltage/current is, rather than having to scroll your eye over to a number and read it.
You could also have the same side illumination with the word Voltage/Current to make the mode obvious too.

The disadvantage is that unless the text is really close to the led it can requires more current to illuminate than have the led shine directly at the person.

Maybe if side mounted leds were placed next to each other, on their long side, with the numbers between them each led would shield the light from the one before it. This would help to concentrate the light right at the text.


Or maybe a transparent overlay could somehow be placed over the leds. So they can instead shine upwards as normal but through sometimes with the number printed on it.

[_Sin]

I reckon you could have a human readable display in only 5 leds, but it would involve waving the board around to be able to read it...

[all_repair]

Maybe a proper display that only turns on for a short while when a button/knob activity.
Or move the display consumption before the isolation converter.

Apple become so rich because of ....

[T4P]

Or maybe a transparent overlay could somehow be placed over the leds. So they can instead shine upwards as normal but through sometimes with the number printed on it.

Alignment ... this is the reason he didn't want to use individual leds to make a segment

[amspire]

Here's an even crazier idea to save micro pins, and probably more money.

No display at all. If you need an accurate output, you attach a meter.

However, the supply has a piezo speaker so it can output voltages and currents in Morse code.  It would mean out is still fully useable without a meter, and you get to learn some Morse. The speaker can be replaced by a led when you needed silent operation.

[free_electron]

Two 3-4 digit 7-segment LCD displays like shown would be cheaper, and easier to read than dot matrix. But harder to drive of course.
Dave.

take a look at this :

67-1795-ND (digikey)

Drive from a pcf21xx display driver. All you need is I2C ... and that you can bitbang. if the dacs in the psu are I2C ... you could get away with an 8 pin CPU. power, ground , i2c and 4 pins for the buttons...

[bxs]

I really think you gone too far, let's see:

- you show something with knobs, them put buttons, ok I can go with that, I don't like, but we need to understand that it need to be small and portable,

- you show the worst LCD case, it only have a common pin, this is crazy, you will almost never use something like that because of the number of pins required, you need to a proper LCD, see the if the price is viable and only then go for a micro, so the search you made for the microcontroller didn't count,

- you show something with independent displays for V/A, then you end up with one, just by that you almost lost me,

- then that ugly thing with the leds, that you have to stop for a minute or tow to decode the thing, men, I could never buy it.

I really think you gone too far... 

But you are in a excellent position, your work don't have to respond to anyone, you are your boss, you can do what you want 

[Bored@Work]

You can't polish a turd, and that display is one in my book.

But you can alter the shades of brown. What about using bi-color LEDs? One color when amps are displayed, the other when volts are displayed.

[chimerahitman]

Has anyone thought about the plexiglass or the translucent plastic getting scratched after a few months of use, which then will make it even harder to read the small text?

Maybe if you have the outline of the selected plastic half-box stick out, in other words when the plexiglass is screwed in it will not touch the surface first, you could get a few months more of clear use, but eventually this product will not last as long.

Stuff gets scratched even if you take lots of care.

If I were going to buy one of these, I wouldn't mind having to pay 1-5 dollars extra in exchange for usability. There are small LiteOn 7-seg LCDs, you could even end up fitting 2 in there allowing both current and voltage simultaneous measurement. Though one could be enough. Point is, numbers plain and simple.

Being able to read both current and voltage at same time will probably do away with the need of using meters, which is the point of this small PSU, to be portable.

[free_electron]

You can't polish a turd,

that myth has been busted. yes you can. but you need tiger poo

[Blue]

Cheap - I wonder...


Hi Dave,

I saw a few moments ago that you teamed up with Adafruits (perhaps you didn't liked the postage hassle anymore).  They want $13 for shipment for the microcurrent converter.  Now, what would saving a few dollars mean in real % terms for the complete price of the usb powersupply? Right - not that much.

(Alternative -  shipment from Hongkong is regarded as quite low (as low as $2 for you mucrrent device)).

[tnt]

I'm leaning toward the same opinion as others:

Although it's a clever solution, I'm not sure the readability is gonna be adequate, especially if you have changing reading for currents for ex and the decade is changing (like oscillate between 19 and 20 for ex).

But sometimes things that seem counter intuitive at first turn out to be remarkably usable, so I'd guess making a quick prototype and see how a small sample of people get used to it ?

[tutman96]

I completely dislike the idea of the decade display. I want to be able to see what voltage the supply is on right when I look at it, not have to decode it. If you want to save money but keep functionality the same, just make a nice computer application that shows the current and voltage. I think you should do that anyways. Maybe put a switch on the board to turn on and off the display. I would buy it if I could set and read the settings from the computer and not waste any power on the leds.

P.S. Was waiting for your battery powered supply to come out. Was going to buy maybe 2, but now you are spending your time on a "toy" that powers 500 mA max and has a display that would take time to decode. GO BACK TO THE BATTERY POWERED SUPPLY!!!

[RJSC]

It's not an optimal display to get a quick reading but I can live with it.
If we still have the USB<->RS232 converter and opto isolator pads we can still get a more natural numeric reading when we have it connected on a computer.

What I think I can't live with is the fact that, as it is, it only allows to operate the PSU up to 299.9 mA
.
We have at least 2.5 Watts available on any USB port, so we can be drawing 500 mA @ 3.3V with no effort at all.

Or is the DC-DC converter only able to go up to 300 mA no mater how low the voltage?

[McMonster]

I personally think that won't be very popular. Cutting the costs is important, but a lot of people would actually be willing to spend 2-4 dollars or even more just to get a nice, readable LCD display they're used to. Too bad supplying two versions, a "DDDD" and LCD one would rise the overall cost (not to mention being a pain in Dave's ass), a direct comparison of sales would be very interesting.

Maybe just make the supply hackable? Some minimal ISP connector (or option for soldering the pins) that would actually double as an extension connector for optional SPI display? You don't like the "bargraph" display, you reflash the micro, connect SPI LCD display, glue/screw it over the old display and everyone's happy. Sure it's still the pain in the ass, but does not add any immediate costs to the device and leaves people with some choice.

[caroper]

You could save even more LED's, and board space, by displaying the value in Binary, It wouldn't be much harder to read.


If you are that determined to cut cost and quiescent current, leave off the display entirely, Just an LED for Source Connected, and LED for Output Enabled and an LED for Overload/CC Mode.


Anyone that needs a portable PSU will also have a Portable DMM if they have their priority's correct.

[Chasm]

Hmm...

A novelty toy that doesn't fart.
I think would pay $5, shipped. And thats only because I could hack it into something a bit more usable. Who cares about the BOM cost if the product is not worth the price?

The display solution is cheap but way to unreadable to be useful. If it is an adjustable power supply  use a real display.  - Otherwise go a step further and only offer a few set voltages. Yes, that means killing even more features.

If neither is an option just glue on the Arduino headers and the sales numbers should go through the roof.

[bullet308]

This is a wonderful exercise in thinking outside the box as content for the blog, and I could see a number of uses for this approach. However, as an approach for a finished product for sale...well, you can see how much pushback you are getting and there is no-doubt a high correlation between forum posters and your customer base.

Perhaps one as a decade display and one LED...

[eternal_noob]

The display solution is cheap but way to unreadable to be useful. If it is an adjustable power supply  use a real display.  - Otherwise go a step further and only offer a few set voltages. Yes, that means killing even more features.

Dave's display solution works better than most would think and the readability is not a problem AT ALL if the voltage adjustment has some kind of a vernier drive to it. Try it yourself, don't let perceptions and old habits get you.

[lk]

Hi Dave,
Its a very intersting idea, for me its no use that i would have to decode that as well. And its already sometimes an issue for me, not being able to decode the amp/milliamp dot on my power supply which causes weird smells.

If the 7 segment displays cause power consumption problems, cant they be driven from a PWM setup, to reduce the power consumption?

Generally i wont have a problem paying 4$ more for a proper display.


-lk

[hlavac]

Even an analog meter would be better than this weirdness.

[IanJ]

Hi all,

Yup I don't like the bargraph idea either.

Quick idea: So why not drive the 7-segment LCD's direct from your PIC/uP.......you don't necessarily need one with a built in 7-seg driver. 3 digits would need 7+3=10 digital outputs or thereabouts.
And if you don't have the I/O then you could also use a BCD to 7-segment IC.......so you could drive the 3 digits (minus DP's) with just 7 total digital outputs (4+3=7).
A nice we routine in your code could scan the LCD accordingly (backplane).

Ian.

[nitro2k01]

I don't know if anyone has mentioned it, but color coding!! The complex variant of this is to have one color for each of the 9 digits, somewhat matching the resistor colors used on hole mount resistors. The less complex option is to give (for example) even digits red LEDs and odd digits green LEDs. This should reduce the "seek time" when having a quick look at the readout.

[SeanB]

I will add my few pence of idea as well.

Use a thinner board, and make the red solder mask on the topside have clear sections where the led displays are going to be. Place a white screenprint around the areas where the digits are going to show, and a grid of white to delimit the digits. Instead of placing the leds on the front, place them on the back so they show through the clear pcb material, using the material as a diffuser. The white mask will help with digit reading, and will also enable you to hide the traces that you will need to common the columns. Rows can be routed on the back side, so that the front panel is bigger display wise, has easy to read masks and has no visible display when off aside from the legends. If you do not want to have multiple vias under the soldermask and screenprint, then you can just use 0R jumpers on the back side to provide the required crossings. Might be cheaper than vias, but more parts to lay out.

Just a thought, I have used thin clear pcb material as a display cover for HP led displays that run on 5mA, they are visible through it when on, and off is a milky white. The on is somewhat diffused, but perfectly legible. It will mean using a thinner board material, or at least a clear one with a reasonable light transmission.

[DavidDLC]

Fugly solution.

As somebody mentioned, I will pay a couple of extra dollars to have 7 segment displays.

David.

[armandas]

I'd love to hear what this guy would have to say about this display idea

[rr100]

Frankly I like these exercises and maybe I could use the concept, in the end anything that works works.
And yes, I know every cent counts but if you're going to turn your product around for some tens of cents and potentially cripple it this is getting ridiculous. To put things into perspective: the ucurrent is like 5 or 10 bucks more expensive on adafruit (which only makes sense of course, as they get their share as well). Then the cheapest shipping to Europe (with no tracking or anything) is $12.63 (next one is $41.20, and is still only USPS). Then of course you're "hitting the limit" and you need to pay VAT on it (=whole value, including shipping), let's say 20% on average (that is if there are no extra fees for electronics). So we're looking at something like $30-$40 extra, assuming no serious bank charges (or overinflated exchange rates), no customs (only VAT), cheap shipping and considering you can do the customs within walking distance (which usually isn't the case of course). Your fifyish ucurrent (or USB power supply or whatever) might easily get intro triple digits when we draw the line. Anyone still willing to cut serious corners for 2$?

[McMonster]

I'd love to hear what this guy would have to say about this display idea

I miss this kind of rant videos. Also the video about the topic mentioned around 9:25 is way overdue.

[FenderBender]

How about concentric circles (or semicircles) of LEDs? Like the ones you see on light up rotary encoders? I would find this more intutitive than reading a bar graph. I made something quickly in powerpoint. It would be something like reading an analog panel meter...."I really kind of like it"

[PA0PBZ]

[Bored@Work]

It would be something like reading an analog panel meter....

But an analog meter with five needles, brrrr

[free_electron]

Use a thinner board, and make the red solder mask on the topside have clear sections where the led displays are going to be. Place a white screenprint around the areas where the digits are going to show, and a grid of white to delimit the digits. Instead of placing the leds on the front, place them on the back so they show through the clear pcb material, using the material as a diffuser.

There's even special led's for this kind of stuff.
go to digikey and serch for TOPLED BOTTOM ENTRY. those ae made for pcb backside mounting and shine through the PCB. ( with or without holes.
if you use a homogenised compound pcb ( and not FR4 ) you can shine straight through them. these led's are often used in instrument clusters for cars or test equipment. if you make a 32 mils thick board this stuff sill shine perfectly through.
you can use blue soldermask to act as a filter. just make openings in the soldermask in the shape of the segments and off you go ...

[G7PSK]

My personal preference would be an LCD and pay a few pounds more simply for the ease of reading without having to think to hard as when I am concentrating on some project or problem I don't want or need extra effort in deciphering the various readings that I am looking at. Choice of equipment is not down to the cleverness of design and cost cutting but how well it serves my needs and ease and accuracy of use. 

[MickM]

Hi;
 Put in the traces for a HD44780 2x16 display.
Let the user solder one in if they want.

If you want to sell 1000+ then you should take a poll on this.
I make too many mistakes as it is.
Having a readout that is a puzzle - with dire consequences is not welcome.

I want to set a voltage and a lower threshold.
Then set current and a high threshold
If either threshold is reached - flash that parameter and beep.
It should have a reset switch.

Mick M

P.S.
What happened to the Bench Supply?

[LaurenceW]

Erm, what's POWERING this thing? A Laptop? well, they tend to come with display built in, yes? measure the current and voltage, and fire the readings back down the USB connection to the host, where a small app displays it. While you are at it, use the keyboard to directly set voltage, current trips, etc...

Or whatever! I think the POINT here is that Dave wants to promote a discussion. It's doing that!

 I tend to agree that the proposed discrete display is harder to read, and while us self-confessed Geeky-types might put up with it, it is a long way from an "accepted" user interface.

I know this next solution means that costs are creeping up again, but think of the possibilities of the extra display info you could offer - better resolution, device power consumption, maybe?
http://www.ebay.co.uk/itm/New-Character-LCD-Module-Display-LCM-1602-16X2-HD44780-Blue-Blacklight-/320931260461?pt=UK_Computing_Other_Computing_Networking&hash=item4ab8fe682d

[caroper]

http://www.ebay.co.uk/itm/New-Character-LCD-Module-Display-LCM-1602-16X2-HD44780-Blue-Blacklight-/320931260461?pt=UK_Computing_Other_Computing_Networking&hash=item4ab8fe682d

That's a good price, I was going to order a few but South Africa is explicitly excluded from the shipping options

[dcel]

     I think that your rant on poor product design sums it up nicely. Now that you are wearing the owner/manager hat, everything has to be built to a "price point". Please consider your potential buyers, they are young students or hobbiest powering their new 'duino' something or other and all they want to do is program the damn thing to make their new LCD say "Hello World". So wouldn't you think that an LCD, say 8x2 or 1x16 for both voltage and current display is the best choice.

     As I type this there is a 8x2 lcd sitting on the keyboard in front of me, and a 16x2 next to the mouse pad, bought a box full of them from a swapmeet, and since I am trying to teach myself PIC programming, I decided that a cool project would be to make a simple voltmeter that I could plug into my uCurrent! (I already finished my "blinky light" project.) And while I was at it, I was going to make two, so I have one for the EEVBlog dummy load that I plan to build.

   Ya, sure, I have five four DMMs but one is at work, one being disassembled/repaired, another is an 400A AC/DC clamp ampmeter, another Wun Hung Lo thats a POS and I dont trust it, and a analog Simpson 260.
Ever thought about doing a Rev 4 uCurrent?

Would I buy one, no LCD, NO!
With an Character LCD, YES! Seven Segment LCD, Maybe...

I will give credit where due, its a novel cost cutting idea, I have done that exact same thing with a device I made years ago for chasing down short circuits in cars, it was the current display in amps using a bargraph, built with a LM3914 and a 25w 1 ohm resistor.

Time to put your Product Design Engineer hat back on....

Chris

[Madsaaby]

If you do it using the 7 seg driver approach then it's potentially 7-8 times the current.
Other arrangements can drop that current, but it's messy, and the requirement to light up more leds over a longer mux time drops the brightness.
And yes, the readability isn't as great. The best way would probably be more expensive rectangular leds and/or reverse mounting with slots perhaps.

Dave.

Hi Dave

Kind of like your idea, but I must agree that the readability is not great. Did you think about rotating it 90 degrees, so you read it top down. Don't know if it's just me, but I find it easier to follow tables vertical than horizontal. But just an idea

- Mads

I.E. 

[LuckyJaker]

Hi Dave,

I really like the blog, but this time you go too far in the name of cost, I don't think that even you would buy such a product !
Quality of information is a premium in a power supply, this one is too error prone and not clear enough.  I have been a
product designer for the last 30 years, and sometimes you go too far in the name of cost, at the expense of usability.

Keep up the good work !

[EEVblog]

Or whatever! I think the POINT here is that Dave wants to promote a discussion. It's doing that!

Yes indeed.
And I like to come up with novel ideas like this, and I think the thought processes and trade-off's are interesting aspects of product design.
Doesn't mean I'm actually going to use it in the final product, I like to shit stir

Dave.

[croyleje]

i think its an interesting idea but i did a little looking you can get single 7 segment led in 200 off quantity for about .22 cents via allied and then you could just multiplex the display. 

[EEVblog]

Would I buy one, no LCD, NO!
With an Character LCD, YES! Seven Segment LCD, Maybe...

Why would such a product need more than just a 7 segment display?

Time to put your Product Design Engineer hat back on....

Ok, I will.
A reflective 7 segment LCD display is much easier to read and has better contrast than a dot matrix character based LCD module.
The module is more expensive.
Although a module can possibly provide for a nicer looking display surround under a clear cover, and maybe smaller overall than two displays? (I'd have to check)

Dave.

[EEVblog]

i think its an interesting idea but i did a little looking you can get single 7 segment led in 200 off quantity for about .22 cents via allied and then you could just multiplex the display.

I've said it before. 7 seg LED display are a bit power hungry.

Dave.

[SgtRock]

Greetings EEVBees:

--I could easily learn to read such a display, no sweat, I love minimalistic design. And, if you want to build locally, and keep Wun Hung Lo, at bay, you are going to have to think smart, because any decent product, will be knocked off. If only there were an easy way to turn off all the LEDs in each string but the one representing the highest number.

--And why not in a kit form?. Now I know DJ says it is too much trouble rounding up all the parts and bagging them etc. Not, so fast. What if the Pick and Place Machine were to just pick and place the parts in a bag. For quality control weigh the bag, at a couple of stages. Include a short piece of solder, and sell it as an SMD Soldering Lesson Project. For help on non-functioning kits, they can ask for help on the Blog. Bobs your uncle.

--I rather like Madsaaby's idea for the display, but I am puzzled why it reads from right to left, instead of from left to right.

--Now, Amspire has recommended including:

 "a piezo speaker so it can output voltages and currents in Morse code.  It would mean [out] is still fully useable without a meter, and you get to learn some Morse. The speaker can be replaced by a led when you needed silent operation.
 
--I think this is an eminently practical solution to the display problem. The only change I would make, is to make it binary, with the dashes being ones and the dots being zeros. This way no one would have to learn Morse Code.

"All business sagacity reduces itself in the last analysis to judicious use of sabotage."
Thorstein Bunde Veblen 1857 - 1929

Best Regards
Clear Ether

[electrode]

It's a novel solution, but it's clumsy, sorry. Is the entire target market of this thing people whose entire time using it is worth less than the $1 to have a better display? Even if you use this thing 5 times, before leaving it in the back of a cupboard, that's ~20c extra per use just to have a readable display.

Also, what's this talk about an "LCD microcontroller"? Sounds like a marketing term. Just use any microcontroller (that first AVR you showed was awesome - ATTINY48-AU for <$1, instead of the almost $5 they cost from element14?!). Then simply bang out the code you need to drive the thing, OR use this document (courtesy of someone in the youtube comments):
http://www.atmel.com/Images/doc2569.pdf

[mikeselectricstuff]

I think using discrete LEDs to make a 7-seg would give it a unique look, and be a good compromise between power and cost
The 3 obvious layouts would be



 *
* *
 *
* *
 *

 **
*  *
*  *
 **
*  *
*  *
 **

***
* *
***
* *
***



The second may be the optimum power-to-visibility as two reds in series will work OK at 5V. With low-current LEDs you should be able to do it with 1-2mA per LED

[mariush]

Absolutely horrible.

There are perfectly good 16x2 lcd screens which are perfect for usability, giving you the ability to show both voltage and amps and other info on screen for about 4$ at 1000pcs : http://www.digikey.com/product-detail/en/LCM-S01602DTR%2FM/67-1781-ND/469805

I'm sure you can find even cheaper, since you sell on your own site a pack of 10 lcd screens with back light for 25 australian dollars:  http://eevblog.com/shop/index.php?main_page=product_info&cPath=3&products_id=5&zenid=3a6dc17b162c1c45563374af8afe579f

And you basically only need 4 data lines for it, and it uses little power... the one that's 4$ above has no backlight but if you're really that concerned you can add a led.

Sorry, but it looks like you're no longer interested in making the product useful and good for all people (including beginners) and you're more focused on keeping the price to the absolute minimum and to automate everything it as much as possible (really, it must be so hard to do wave soldering or solder 6 pins manually or hire someone to do it)

Sounds like pinching pennies to be able to add to the profit margin and still include that 40% or whatever distributors like Adafruit ask for, as you said in the live show...

[EEVblog]

I'm sure you can find even cheaper, since you sell on your own site a pack of 10 lcd screens with back light for 25 australian dollars:  http://eevblog.com/shop/index.php?main_page=product_info&cPath=3&products_id=5&zenid=3a6dc17b162c1c45563374af8afe579f

I got those for FREE.

Sorry, but it looks like you're no longer interested in making the product useful and good for all people (including beginners) and you're more focused on keeping the price to the absolute minimum and to automate everything it as much as possible (really, it must be so hard to do wave soldering or solder 6 pins manually or hire someone to do it)

What has the beginner got to do with it? This was never going to be a kit.
I like mucking around with novel ideas like this, I find it enjoyable. It's just an idea, sue me.

Dave.

[Rutger]

I do not like the idea, you might save money on the BOM but you would loose much more in potential sales.

My suggestion is to multiplex the 7 segment LED display and also use an 555 timer to turn the display off after say 20 seconds or use the micro to turn off the display after a set time. Use the same LED display for both voltage and current like suggested by you and others.

Keep up the great job Dave, we love 'most' of your projects ideas.

Rutger

[HLA-27b]

Fooling around with solidworks I got something like this.
it works with LTST-C230KT
http://www.digikey.com/product-detail/en/LTST-C230GKT/160-1188-2-ND/269235
The cheapest reverse mount led on digikey
All slots to be machined with 1.6mm dia. router bit

....decimal points look a bit wierd, might play a bit with these



I can send the cad files if there is interest

[DarkPrince]

I really can't say how I feel about this design... I never really tried to read one in real life. I like it because it sounds fun, and non the less it almost makes a dot-matrix display so, anyone say custom firmware scrolling message?  I am not 100% sure about it in the environment it is in, but I really can't comment unless I try. So hard to imagine. 

HAL-42b... pushed those a bit too close together? At the moment looks like a pile of leds. Though could be the CAD'ness of it.

[EEVblog]

I really can't say how I feel about this design... I never really tried to read one in real life. I like it because it sounds fun, and non the less it almost makes a dot-matrix display so, anyone say custom firmware scrolling message?  I am not 100% sure about it in the environment it is in, but I really can't comment unless I try. So hard to imagine. 

Yes, I think it needs to be prototyped and used in person to see how well it actually works in practice.
I think those poo-poo-ing the idea outright sight unseen are maybe being a bit close minded (but I understand their reaction). It could very well suck of course, but then again it may not and be quite usable.

Dave.

[dolabra]

Is it April Fools again? 

[HLA-27b]

Ok how about this

[EEVblog]

Ok how about this

Less readable than my one I think, but it certainly looks funky!

Dave.

[free_electron]

Why would such a product need more than just a 7 segment display?

a few things come to mind...

top line : Voltage
bottom line : current.

you can change text to OVERLOAD on overcurrent
you can display CV or CC .. you can display OUTP.OFF if the output is disabled...

And, when you power up you can display EEVBLOG - USBPSU .. for a second or so..
that alone should convince you !

A reflective 7 segment LCD display is much easier to read and has better contrast than a dot matrix character based LCD module.

use a black on yellow one with yellow backlight. or go for the DOGM ones in inverse ( white backlight , black display with white text. looks like a VFD when on. very pleasant and high contrast.

you could use the 2 line one. or the 3 line one , make a custom charset so the top two lines display large digits and the bottom line display small font. Or go for the 128x32 pixel or 96x32 pixel one. small ,compact, thin, and driven via SPI...

[EEVblog]

FYI
The LTC-4724 display on my prototype at a reasonable brightness takes 60mA or so from the USB (+ micro + circuitry) for two displays.

There aren't a huge amount of display options for a credit card size case.
The standard 8x2 LCD modules are too big at 53mm x 32mm, and would need to stick out the front of the case/front panel.
Bit of a shame because I think I can get those at a reasonable price.

I've always liked the 40mm x 20mm DOG displays:
http://au.mouser.com/ProductDetail/ELECTRONIC-ASSEMBLY/EA-DIPS082-HN/?qs=s9z6UkyjM7oML9NbXKYovN7SKL8TdxR%252bTHPKLsXF5HE%3d
But at almost $10 with no second source, it's not an option.

And I still haven't found a viable option the housing I showed in the 2nd video. Some have come close, but have fallen over on the minor dimension details.

It's one tricky design...

Dave.

[dh]

I think there's room for improvement on the glance-readability though. I would like to suggest that your acrylic screen have either silkscreen or back masking, so that when an LED is lit, you see the a lit numeral that it corresponds to. In practice, you'll end up with a '2' down there, a '9' up there, and a '5' somewhere in the middle, but when you glance at it, your brain will register "2.95" and not RED RED RED.

It actually seems a little retro-chic, if you think about it!

The most important part is that it does the job with the least amount of cost and energy. Good luck!

[EEVblog]

a few things come to mind...
top line : Voltage
bottom line : current.

That has nothing to do with dot matrix vs 7-segment. I could also use two 7 segment LED or LCD displays like I did in my protos.

you can change text to OVERLOAD on overcurrent
you can display CV or CC .. you can display OUTP.OFF if the output is disabled...

And, when you power up you can display EEVBLOG - USBPSU .. for a second or so..
that alone should convince you !

Sure, but I don't deem any of that as being essential.
On 7seg displays you can blink things like the decimal point or entire display to indicate CC mode. (My prototypes do this, and it works fine)
7seg displays can also display limited char info.

use a black on yellow one with yellow backlight. or go for the DOGM ones in inverse ( white backlight , black display with white text. looks like a VFD when on. very pleasant and high contrast.

Sure. Show me one at a reasonable price that fits a credit card size case...

you could use the 2 line one. or the 3 line one , make a custom charset so the top two lines display large digits and the bottom line display small font. Or go for the 128x32 pixel or 96x32 pixel one. small ,compact, thin, and driven via SPI...

Graphic can get me the size (I've investigated these extensively for my uWatch), but not a reasonable price.

Dave.

[HLA-27b]

Less readable than my one I think, but it certainly looks funky!

Dave.

It has a sort of continuity feel to it because it warps around as you rotate the knob, both unnecessarily hard to read if you ask me.

Do you have a link to the box dimensions?

[EEVblog]

It has a sort of continuity feel to it because it warps around as you rotate the knob, both unnecessarily hard to read if you ask me.

Yes, I like that. But knobs have been vetoed on this design, as they protrude too far.

Do you have a link to the box dimensions?

http://www.altronics.com.au/index.asp?area=item&id=H0215
http://www.altronics.com.au/download/ndb/specifications/h/H0212.pdf
(G434 90x50x32)

Dave.

[PeteInTexas]

I don't like it. All that solder is sure to add to the overall weight of the device. 

I still don't understand the resistance to using the at least 14 inch display that is already attached, if display cost ($ and current) is the issue.

I still don't understand why USB power can't be a source in the battery powered PSU instead of having yet another device.  Multi-taskers are valuable for space constrained hobbyist.

[dolabra]

How about combining a cap-touch slider and a bar graph?  that might be a neat effect to increase and decrease values?

[Zad]

I have myself designed a system which used non-linear multi-dial virtual meters. That was on a dot matrix LCD panel though, and the sub-ranges were customised to allow the operator to see how a system was behaving. People think all display ranges have to be linear to be optimal. Not so! Audi speedometers have the scale compressed above 100MPH. Having said that - Are you raving mad? I can just imagine what a doppleganger Dave Jones would say about the decade display. Anglo-Saxon expletives would be in full flow.

I'm afraid using an LCD 2x8 or 2x16 module is just too good an option to resist. Cheap, multiple sources (possibly thousands), low current, flexible, hackable (anything with an LCD text display is just asking to be repurposed). The top seller on Ebay at the moment (854 sold) is selling 16x2 LCDs for £1:82 INCLUDING postage!

I don't care if it is too big! Change the case! If you are going to use enclosure size to constrain the design so tightly then something (cost and functionality) will have to give. If a product looks like a cheap toy then people won't buy it, no matter how good it is. Each cent saved is another cent in Sagan's education fund, but only if the product sells. I realise the reasons for sourcing from major distros like Digikey, Element-14 etc, but if you are pushing the costs and are seriously looking at 1000qty then you need to look at the more direct distributors (Arrow, Avnet).

In my opinion, any PSU needs a real time current display, so having a display that reads current when you press a button is useless. I need to know how the current is behaving as I wind up the voltage, no matter what project it is that I am undertaking. By the time my brain has decoded which particular red/green blob is being displayed, something could already be getting toasted.

If you simply must go with individual LEDs, how about going with a logarithmic scale? 1/2/5/10/20/50/100/200/500/1000 mA etc. Charlieplex them to save pins if you have to. Concentric dials is way too confusing,

[EEVblog]

I still don't understand the resistance to using the at least 14 inch display that is already attached, if display cost ($ and current) is the issue.

I want it stand-alone. Having to have a PC run a program just to display and adjust the voltage is a PITA. I want it right there, in my face, all the time, for any 5V USB source.

I still don't understand why USB power can't be a source in the battery powered PSU instead of having yet another device.  Multi-taskers are valuable for space constrained hobbyist.

This is supposed to be a much lower cost, smaller, and simpler supply.

You don't have to like the idea, it's ok.

Dave.

[Zad]

I still don't understand the resistance to using the at least 14 inch display that is already attached, if display cost ($ and current) is the issue.

As I understand it:

1. Because the USB data lines would then have to be isolated, adding considerably to cost.
2. Because it is designed not just to run off a computer but a USB power adaptor plug pack.

Having said that, I wonder how much a "headless" (i.e. no display or controls) unit would save in production cost, aside from the switches and display, the case would be cheaper too, as it wouldn't require a custom front panel.

[Mercator]

Ok how about this

Less readable than my one I think, but it certainly looks funky!

Dave.

It took me a little longer to understand the concept the first time around, but after that it is actually more readable. You could have two of those circles (voltage and current) with the buttons placed somewhere else. It is very close to an analog clock. It might also look better when it scans around. The vertical graph of your design goes from all lights on to all lights off when it goes past 10. A clock has a better continuity in that respect. The inner ring will spin a lot faster than the outer rings, making it clear that those represent a less significant digit.

Another advantage: You got a brighter and more power efficient display, because there are only two or three lights on at any given time.

[notsob]

If you use a clock face start 1 at 1 o'oclock - so us old farts can read it without thinking

[EEVblog]

1. Because the USB data lines would then have to be isolated, adding considerably to cost.

For USB, yes. For serial RS232, not as much (reasonable in fact), just a pair of optocouplers.

Having said that, I wonder how much a "headless" (i.e. no display or controls) unit would save in production cost, aside from the switches and display, the case would be cheaper too, as it wouldn't require a custom front panel.

It's significant.
You drop a dollar or two for the display, more if you are looking at a nicer module display solution.
You drop the need for the custom perspex cover.
You drop a few tens of cents for switches (rotary encoders + knobs are much less expensive)
The case can be more rugged and streamlined because it's the full case. And it easily fits into the 90x50mm case.

Certainly a good case can be made for such a design (and likely popular?). But I personally would find it much less convenient.
I have the BOM spreadsheet, I could run the numbers...

Dave.

[Psi]

Another option is just preset voltage/current values that you can step through with the buttons and a single led per preset to show it's active.

With the 32 leds you have in the matrix now you could have 32 preset voltages.  From 0-15V in 0.5V steps.
The presets could be non linear so 3.3V and 1.8V are available at the cost of other steps that are unlikely such as 14.5V or 8.5V. Or just have more LEDs, they're cheap and never on at the same time so don't effect power consumption.

For the current limit 0-500mA could be divided into steps of ~16mA as well. Though the current scale would have to be linear as it's used to display the actual current as well.

You could even have a way to change the values with special button combos by having a few "custom" presets that are stored in eeprom with a blank box on the PCB/case for people to vivid-in what voltage they have set their unit to.  Or even have all presets reprogrammable.

[m12lrpv]

I like the dial option if you have the space but only in a Multi Dial configuration.

It is not new and is not difficult to read.

[TerminalJack505]

You can go the opposite route and do something like they did on the Nike+ Fuelband.  They used a 5x20 matrix of LEDs.  Mike from Mike's Electric stuff did a teardown.

The 'cool' factor might help sell some units.  If you make the display a separate module then you can have standard and deluxe versions of the power supply.  The standard version can use the DDDD.  You can then sell the 5x20 matrix as a standalone product.

[dda]

Bah, haters gonna hate. It isn't a horrendous design.

Of the actual good (not LED/LCD, I mean get over it) suggestions here, I like the arc, but that is more suited to using with a dial, and I like the horizontal version of daves (except why go right to left? surely low numbers to the left is more readable).

At least dave now knows how to get people to comment on videos.

[dh]

As I mentioned above, I think the whole idea is perfectly salvageable if you put numeral masks over the LEDs, giving you a number readout instead of just a position readout.

You could put this on the front or back of your acrylic cover.

[LEECH666]

I kind of like the idea of the bargraph display, however I would prefer to have a number (digit) next to each LED and not just a single one on the side. That's really just nit-picking.

(Take a look at my PDF)

Sure it wont be the most readable display solution but if I consider how cheap it is I certainly would give it a thumbs up.

Note: I'll most like not buy this product tho, as I don't really have a need for a mobile PSU (yet).

[HackedFridgeMagnet]

I think the idea is worth testing, It may work nicely once your used to it, I don't think it would be very hard to read. It's generally not like a multimeter where the voltage is constantly fluctuating.

What about a fourth column so the decimal point doesn't move, the unused column just doesn't lite up.

And what about when you are setting voltages and currents, the display should be showing the set level not the actual level.

ps. I don't like the case much, prefer a flat bottom.

[lk]

I would still if there is room in the device put in a hd44780 compatible display, like the one i have here that is consuming less than 20mA at 5v, including a shiftregister. I'm sure they can be found to run off  a lower voltage.  ofcourse i don't know if there is room in the enclosure for it.

With a proper LCD display, you can at one glance see current,voltage and set current and set voltage, makes it much more usable. And my guess is that writing the interface software is properly easier for one of these displays as well, as the libraries are easily available. And you  can get away with fewer pins on the micro aswell.

Is this something that is designed to be easy to use or something that is intended just to be on display as a curiosity, i would prefer the first

And if they are remaking "Forbidden Planet" the decade display would make good sense for a displaying power output in the Krell power plant. 

-lk

[EEVblog]

ps. I don't like the case much, prefer a flat bottom.

I have yet to find a suitable practical alternative unfortunately.

Dave.

[amspire]

I do find it hard to imagine anyone not willing to pay an extra few dollars for a LCD display.

The discreet diode idea is basically a new version of the 1950's Dekatron counter tube. They could wait to ditch the Dekatron's back then. I cannot see people queuing for the return of the concept.

Is the design using resistive potentiometers for voltage and current, or a digital pot + Dacs? If it is using Dac's, then they can be replaced by the PWM design from the General Purpose Power Supply thread. The latest code there will run on a Tiny fine - haven't tried it on a PIC, but I assume the idea will work on a PIC. It will easily give 1mV resolution if you need it, and true 1mV steps.

Richard.

[robbyn]

There is an option that you didn't consider (at least, you didn't mention it in your video) it's using a software driver.
Only the biggest atmegas have built-in lcd drivers, but it's very easy to do this by software.
Atmel has an app note about it:
http://www.atmel.com/Images/doc2569.pdf
Of course, it's not as cheap as your solution, but you would still be able to use the cheap attiny48, it's more efficient, and more user-friendly.

[EEVblog]

Is the design using resistive potentiometers for voltage and current, or a digital pot + Dacs? If it is using Dac's, then they can be replaced by the PWM design from the General Purpose Power Supply thread. The latest code there will run on a Tiny fine - haven't tried it on a PIC, but I assume the idea will work on a PIC. It will easily give 1mV resolution if you need it, and true 1mV steps.

PWM of course.

Dave.

[cheepokleebo]

Another option is just preset voltage/current values that you can step through with the buttons and a single led per preset to show it's active.

With the 32 leds you have in the matrix now you could have 32 preset voltages.  From 0-15V in 0.5V steps.
The presets could be non linear so 3.3V and 1.8V are available at the cost of other steps that are unlikely such as 14.5V or 8.5V. Or just have more LEDs, they're cheap and never on at the same time so don't effect power consumption.

For the current limit 0-500mA could be divided into steps of ~16mA as well. Though the current scale would have to be linear as it's used to display the actual current as well.

You could even have a way to change the values with special button combos by having a few "custom" presets that are stored in eeprom with a blank box on the PCB/case for people to vivid-in what voltage they have set their unit to.  Or even have all presets reprogrammable.

Dave,
I think that you got us all excited with the first and second prototypes with the 7-segment Leds and the big knobs (which we all secretly love) and now this is a bit of a let down. I am just afraid that it will be a bit confusing when reading, let's say 14.58 - is it that or 25.69.
So I think the presets could be, as mentioned above, a bit more user- friendly. Give them 10 presets for both V and I. And an option of setting their own voltage by plugging in  their  multimeter and setting it with that.
On the other hand I am sure one could get used to the decade display in a short time. I am getting real quick at reading 8 bit binary numbers on my "byte" display.
Great videos - love them - By the way, on your PICKit 3 review blog you have about 100 hits which are not your regular viewers- I made my students watch it so they could learn how to do a "proper blog" and not just a boring report.
rich   

[EEVblog]

I think that you got us all excited with the first and second prototypes with the 7-segment Leds and the big knobs (which we all secretly love) and now this is a bit of a let down.

Yes, it was probably a mistake to show those.
And with hindsight with both of these PSU design series, possibly a mistake to show anything at all! 

Dave.

[HLA-27b]

Now this is quite pleasing, absolutely no frills and only 14 leds. Does everything a user interface needs to do and no more.
It currently reads 5.70 Volts
Pressing the encoder button toggles between Volts and Amps
The scale can be used as 60mm straight edge and don't worry about the knob height as it does not go any higher than the screws.




The case used is http://www.digikey.com/product-detail/en/1591MSBK/HM361-ND/284747
This is a far better case because it does not have side cut outs.

[EEVblog]

Now this is quite pleasing, absolutely no frills and only 14 leds. Does everything a user interface needs to do and no more.
It currently reads 5.70 Volts
Pressing the encoder button toggles between Volts and Amps
The scale can be used as 60mm straight edge and don't worry about the knob height as it does not go any higher than the screws.

How do you know the absolute position of the rotary encoder?
How can you get a grip on the knob?

(awesome graphic BTW, and I like the concept)
I was going to greater than 12V too.

The case used is http://www.digikey.com/product-detail/en/1591MSBK/HM361-ND/284747
This is a far better case because it does not have side cut outs.

Not having side panels is a big down side. You have to get the case punched. Unless you use the top side mount USB connector and vertical binding posts that I did in my prototype. I've been there, I've costed it and considered it long ago, it wasn't the cheapest solution IIRC.
And the rotary encode and knob make the height much bigger than needed.

Dave.

[HLA-27b]

How do you know the absolute position of the rotary encoder?

some sort of absolute encoder, BCD, Gray code, anything..

How can you get a grip on the knob?

Put a big coin or 2032 on the table and try to rotate using thumb and index finger, it is actually quite ergonomic.

(awesome graphic BTW, and I like the concept)
I was going to greater than 12V too.

NP here,  rinse and repeat as needed.

Not having side panels is a big down side. You have to get the case punched. Unless you use the top side mount USB connector and vertical binding posts that I did in my prototype. I've been there, I've costed it and considered it long ago, it wasn't the cheapest solution IIRC.
And the rotary encode and knob make the height much bigger than needed.

I would much prefer to punch it out. Simply get your hands on something like this and ask a machinist friend to make you the punch(es) that you need from tool steel (you need a machinist friend for this to work). After that any hole in any panel becomes a single 3 second operation for you.
Otherwise you have 3 different panels which still require assembly. Also the seam points where these panels touch each other will be a weak spot. They will flex and squeak and reduce the rigidity of the whole thing. Your customers will notice it.  Actually it might be possible to devise some sort of finger joint to remedy that but why complicate your life and run the risk of increased returns?

[Psi]

I do quite like that design.

[nitro2k01]

I don't know if anyone has mentioned it, but color coding!! The complex variant of this is to have one color for each of the 9 digits, somewhat matching the resistor colors used on hole mount resistors. The less complex option is to give (for example) even digits red LEDs and odd digits green LEDs. This should reduce the "seek time" when having a quick look at the readout.

Since my post seemed to go unnoticed, I'll try again ^^^^

Someone mentioned using green/yellow/red or something like that, like an audio level indicator. In my opinion, that's just fancy but useless. My suggestion would, I believe, cut down the split second it takes for you to find to the right digits, because the color tells you something about the digit.

[PA0PBZ]

I do quite like that design.

Me too, but I can see a few problems, for example how to switch from V to A? I guess you could push the knob if you can find a BCD encoded rotary thing with push capabilities...
But what's worse is, how are you going to read the momentary value of the current? A motorized knob? 

[dcel]

     Build the DDDD up and let us see what it looks like. Spin one with an LCD as well, 7seg or dot matrix. Lets see the resulting feedback on each version. You have to build something that will sell, if everyone responding doesnt like it, it probably wont sell. Yes, you can only make some of the people happy some of the time, not everyone happy all the time.

     Ive built and owned a binary clock and I can say that it doesnt take long to train oneself to know what time it displayed. That is time, and you may have the time to determine what time it is, but standard 7seg clock is much faster to "read".

     I want to know the amount of current being drawn "instantly". I finally own a power supply with voltage and current displays and I really like knowing at a glance what the output is, and I REALLY like having constant current mode. Would I buy another power supply without these features? No! And I am actively looking for another PSU to complement the one I have, just higher current. Yes, a small USB PSU would be nice to have, provided the feature set is there. Do I want a uSupply? Hell yes! That unit has great features, provided you dont try cost cutting it down to a price point.

Chris

[blackdog]

Hi,

Just to make things clear...

The max power of USB-2 is 5V 0.5A = 2,5Watt
Efficiency of DC to DC is approximately 75%
The no load current is in the range of 50mA, already 10% of Max.

If Dave is using a 5V to 24V converter the max output current will be less than 100mA
If he is using a 5V to 15V converter the max output current will be less than 150mA
There will never be 0.5 or 1 ampere range. ( not with a cheap DC to DC )

Dave can you shine some light on wat type of DC to DC Converter is used?

Kind regarts,
Bram

[HLA-27b]

I don't know if anyone has mentioned it, but color coding!! The complex variant of this is to have one color for each of the 9 digits, somewhat matching the resistor colors used on hole mount resistors. The less complex option is to give (for example) even digits red LEDs and odd digits green LEDs. This should reduce the "seek time" when having a quick look at the readout.

Since my post seemed to go unnoticed, I'll try again ^^^^

Someone mentioned using green/yellow/red or something like that, like an audio level indicator. In my opinion, that's just fancy but useless. My suggestion would, I believe, cut down the split second it takes for you to find to the right digits, because the color tells you something about the digit.

I like drawing. What I don't like is writing 

[EEVblog]

Dave can you shine some light on wat type of DC to DC Converter is used?

I showed it in the housing video, a standard 2W SIP 5V-5V isolated converter.
You don't need any more than 2W to make use of the full 500mA USB, as the converter is only 80% efficient at best, meaning 2W output maximum.

Dave.

[Psi]

Here's a quick and dirty mockup of the side led idea i described earlier

It would work best with really wide angle leds, However you would get some back scatter from the rear of the adjustment led

[Madsaaby]

--I rather like Madsaaby's idea for the display, but I am puzzled why it reads from right to left, instead of from left to right.

That's a good question actually Didn't really think about it, think I did it this way because LSD used to be to the right.. But it is kind of reversed compared to how we read things usually, when I think about it. Maybe it would be better to flip it..

- Mads

[HLA-27b]

Here's a quick and dirty mockup of the side led idea i described earlier

It would work best with really wide angle leds, However you would get some back scatter from the back surface on the adjustment led

Nice but surface mount things might peel off in use. Imagine that the user puts it in his backpack together with a bunch of other tools - screwdrivers, side cutter soldering iron etc. etc. Chances are that a few leds might be missing when he pulls it out again.

[hlavac]

There is supposed to be a clear perspex plate over the thing, no?

[Psi]

Yes, LEDs will be protected. The case Dave plans to use will have a transparent top screwed to it.
The tack buttons will be much taller than in my pic and protrude through holes in it.

I actually found a STEP model of a clear case i could import into Altium for the 3D view, but then i remembered that all models in summer 09 are solid. I could do it with an extruded box i guess.

[HLA-27b]

Yes, LEDs will be protected. The case Dave plans to use will have a transparent top screwed to it.
The tack buttons will be much taller than in my pic and protrude through holes in it.

I actually found a STEP model of a clear case i could import into Altium for the 3D view, but then i remembered that all models in summer 09 are solid. I could do it with an extruded box i guess.

Could you export the PCB in some 3D format? I'd like to try it  with transparent box in SolidWorks.
STEP IGES etc. should be fine

[eternal_noob]

Yes, I think it needs to be prototyped and used in person to see how well it actually works in practice.
I think those poo-poo-ing the idea outright sight unseen are maybe being a bit close minded (but I understand their reaction). It could very well suck of course, but then again it may not and be quite usable.

Dave.

I have tried this solution for a simple turns/event counter and it worked out just fine. The first glance at the display is admittedly a little bit troublesome, but in a PS where you know what number is going to be displayed next, by turning a knob either up or down, it is NOT really a problem. Thats because your brain already know where you were AT. Of course, I would never have used this solution, lets say in a bench volt meter. That will suck bigtime!
But anyway, I will warn against using type of display. People tend to choose form over function, not function over form, and those who do will almost hate you for doing this ''gruesome'' thing to them.

[free_electron]

Yes, I like that. But knobs have been vetoed on this design,

What about edge rollers ? They exist in encoder form. Panasonic makes those ( amongst others ). Digikey has em. Behave like a rotary encoder and include the push feature.

Remember old style transistor radios with the little wheels sticking out the side. You would roll over them with your thumb. That's what i'm talking about. They exist as encoder.

As for cheap lcd Look for a COG type display. You could even go for a 3310 style cellphone display. These are dirt cheap on ebay.

[Psi]

Yes, LEDs will be protected. The case Dave plans to use will have a transparent top screwed to it.
The tack buttons will be much taller than in my pic and protrude through holes in it.

I actually found a STEP model of a clear case i could import into Altium for the 3D view, but then i remembered that all models in summer 09 are solid. I could do it with an extruded box i guess.

Could you export the PCB in some 3D format? I'd like to try it  with transparent box in SolidWorks.
STEP IGES etc. should be fine

I found an option to do it. There is an opacity slider i didn't notice.

Here's a few model exports, in case you want to have a play.
I've not checked exactly what got exported though.
http://psi.abcom.co.nz/models.zip

Here's the updated example with a case and cover.

[EEVblog]

What about edge rollers ? They exist in encoder form. Panasonic makes those ( amongst others ). Digikey has em. Behave like a rotary encoder and include the push feature.

Remember old style transistor radios with the little wheels sticking out the side. You would roll over them with your thumb. That's what i'm talking about. They exist as encoder.

I've used those.
Think I briefly considered them on an old proto I think, but they don't really offer any major advantage over tact buttons, and you have to have a cutout slot on the side of the case for them, unless you can mount them on the case end. Devil is in the detail as always.

As for cheap lcd Look for a COG type display. You could even go for a 3310 style cellphone display. These are dirt cheap on ebay.

They are usually not designed for nice rigid PCB mounting. And many physical variations exist that can cause supply headache. The good ones like from Newhaven are not cheap.
I have found 8x2 character based displays cheap, but they are really thick and the bezel will have to protrude through the front panel.

Dave.

[MagFlux]

Dave, your original idea is still the best seen here so far. You may want to play with the LED spacing to get an idea on how well the eye can detect a discernable pattern. I believe that after using it for a while it would be like reading an analog meter by seeing a postion (or pattern in this case) rather that a number. If you want to get more precise silk screen a grid with the number values over the coresponding LEDs.
This silk screen should be on the back side of the front panel and the panel as close to the LEDs as possible.

[EEVblog]

Dave, your original idea is still the best seen here so far.

I think my idea has been pretty comprehensively shot down in flames. Based on all the comments and feedback, hardly anyone wants it or thinks it's a good idea.
I suspect that an LCD solution is the only way forward.

But even if I change the LCD, I'll likely still get hounded on the case  , although no one has yet come forward with a suitable alternative that meets the criteria, and I have not found one myself.

Dave.

[Psi]

But even if I change the LCD, I'll likely still get hounded on the case  , although no one has yet come forward with a suitable alternative that meets the criteria, and I have not found one myself.

What about the small red one of these http://www.hammondmfg.com/1553colors.htm

With nice rubber sides and enough room to mount an LCD on the top yet thin enough to fit into a laptop bag.

Even comes in a nice uCurrent style red according to the website (although the Digikey pic of it is a totally different red so i dunno which red is correct ? )
$4.34 in qty 500, so more expensive than your other case, but it is really nice.
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=HM1149-ND

[EEVblog]

What about the small red one of these http://www.hammondmfg.com/1553colors.htm
With nice rubber sides and enough room to mount an LCD on the top yet thin enough to fit into a laptop bag.
Even comes in a nice red (although the Digikey pic of it is a totally different red so i dunno which red is correct ? )
$4.34 in qty 500
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=HM1149-ND

About 3 times the price of my current one, and bigger.
The top must be machined out for the LCD.
Not tall enough to be used as half case.
Only one end removable, so the other end for the USB connector has to be machined out.

No joy.

Dave.

[MagFlux]

Dave, my response to critics that may not like it because "it's different" is as follows...
"Damn the torpedoes, full speed ahead"
However if you are somewhat convinced by them, let's move on.
Regarding the switches, can you price justify a micocontroller with touch capability and
do without mechanical switches and have touch pads instead?
The design would be free of moving (read breakable) parts and be easier to place where you want them.

[HLA-27b]

Found the original lid 
Also had to trim the pcb corners the mounting holes don't interfere.
Unfortunately the decals did not come though, and the cylinders on top of the buttons dissapeared.

What's interesting is that there are pcb spacers on the lid as well. So using these is possible as well.

[SeanB]

The punches are available off the shelf, and are even available in profiles for most common switch holes ( flat sides and with a notch for alignment) quite cheaply. Of course the major issue is that the substrate will have to be heated to around 59C to prevent cracking on thick panels or brittle plastics. If it is to be a custom punch they generally are made by using a copper negative master in a spark eroder to etch a tool steel bar to the required profile. Slow but makes a near perfect hole.

[free_electron]

if you are going to produce these in quantity : have the lid laser cut or waterjetted. that can be done for a few dollars per unit...

Why not custom mill an enclosure. the guys from Salae can have it done for their products. they buy a few hundred at a time in china for 4 to 5 dollar a pop ... then you can have a nizce anodiced , custom shaped enclosure with all the holes cut in it. you can even engrave the legends ....

[asgard]

One thing about that display.  With the configuration of a triple-decade display with (obviously) low duty cycle, it becomes possible to use a column-amplified Charlieplex configuration, so that 30 of the LED's are addressable with only six pins.
Only the tens-(digits) need to be connected separated from the main array.  Only 6 pins with three-state addressing, three NPN transistors, nine resistors for 30 of the LED's.  Add two more LED's, two resistors, and two more pins for the tens place and Bob's your uncle.  Almost exactly what I have done for my bidirectional LED optics project.  That could substantially reduce the part cost for the MCU in a huge way.

J.R. Stoner

[asgard]

Following up to my own post (bad form, really)  You could use differently-colored LED's within each of the decade columns  in small groups to aid readability.  Pick five colors and use groups of two:

wht red red org org ylo ylo grn grn blu blu (white can be the decimal point or the tens digits).

J.R. Stoner

       

[Joshua]

What about a row of LEDs that represent 1-15 volts(or whatever the max voltage is)

Then another row of LEDs underneath that represents the tenths of volts (0.1, 0.2, 0.3,etc..)

I'd personal think it would be easier to read than the matrix design.

[ovi_mv]

Hi

First things first the LED decade is a nice idea and a practical one (i really liked my LED wrist watch ), still regarding the USB supply i have a hint about a possible option and i hope it will make a difference for David ... but the are 2 uneasy details.

1. It is a 1bit B/W graph LCD 96x64, with LED backlight (extremely popular NOKIA LCD spare)
2. It is available at a good price on Alibaba (China).

the good aspects about this solution are

1. the fact that it's cheap 0.70$US /100 (one hundred pcs), above 1k i saw that is possible to shave off about 9-11 cents
2. has SW support (i used it with cortex M0/M3 but HAL drivers for atmega can be made)
3. needs only 4 wires for data SDA/SCL/RST/CE
4. there 2 display options one with solderable flex PCB type connector, another with hirose DS-10 connector both share the same physical layout and dimensions
5. the DS-10 connector version has a very neat 4k color upgrade option (another LCD from nokia)
6. IMHO this LCD will be around at least for the next 5 years.

If this can be usable i would be more than happy to provide the details
Best regards

Ovidiu

[EEVblog]

Regarding the switches, can you price justify a micocontroller with touch capability and
do without mechanical switches and have touch pads instead?
The design would be free of moving (read breakable) parts and be easier to place where you want them.

You can't have touch switches unless you have an active PCB for the front panel.

Dave.

[EEVblog]

If this can be usable i would be more than happy to provide the details

Yes, please supply the supplier details.
Thanks.

Dave.

[Psi]

It is a 1bit B/W graph LCD 96x64, with LED backlight (extremely popular NOKIA LCD spare)

Something like that could possibly be attached to the PCB over the top of the unpopulated pads for the decade display.
If the supply of the LCDs ever ran out or there were issues getting them they could be left out and the original decade leds soldered on instead.

[amspire]

Just had a look at the prices for the Nokia LCD displays on Aliexpress, and they seem to be ridiculously low. 320x240 serial interface colour displays for a few dollars. I didn't see the $0.70 displays, but it was easy to get under $2 for just 10 off quantities including shipping for monochrome displays.

Is this a real price, or has the Nokia production crashed so far that the market is flooded with displays.  It seems to me that the bulk of the cheap displays are Nokia.

I wonder how long these prices will last? It is hard to know. Considering the size of Nokia and how quickly their sales have been dropping, there could be warehouses swimming in unused displays.

[EEVblog]

I don't see the $0.70 ones either, more like $1.20 - $1.50 or so which is still quite cheap.
But there are just so many variants it seems endless...
I think the trick if you design one of these in is to find someone with 5K+ and negotiate a price for the whole lot!

Dave.

[EEVblog]

Just got a quote from a local plastic place for the custom polycarb cover, $2.40 for 1000. That's seems fairly expensive to me?
Anyone know any good places that can do it cheaper?

Dave.

[EEVblog]

The Nokia 5110 displays seem nice, and appear to come attached to a small board with 0.1" header. Much easier to use and mount than the others.
But about double the price what I can get the 8x2 line LCD modules for.

Dave.

[HLA-27b]

Just got a quote from a local plastic place for the custom polycarb cover, $2.40 for 1000. That's seems fairly expensive to me?
Anyone know any good places that can do it cheaper?

Dave.

Given the tiny quantity it is actually a good price, considering that they have to make molds for it.
Have you considered having a sheet metal lid? Given the original case that you are using it will be possible to have a very simple and robust single piece lid like below. You might want to inquire a sheet metal place for something like that. It might come cheaper as it has only two bends and one laser cutting (or blanking, even cheaper) operation. Hell the bend operation could even be ganged up so as to have 2 bend operations for every 20 pieces
1.5mm aluminium would be suitable material.

If interested I can draw it for you in no time.

[DarkPrince]

This is very interesting. Dave walks out with an idea and he got blown up into pieces. What else is a community for?  I am happy, but I am also sad. I think the main reason (since I don't really need a USB PSU) for the product was for the amusing display aspect of it with the low cost factor. Now just a 'normal' tool. Though a little more stable with the community. Still interested. 

[EEVblog]

Given the tiny quantity it is actually a good price, considering that they have to make molds for it.

No moulds, they just cut it out from a larger sheet from stock. It's square with 7 holes in it. Probably the simplest thing possible for them.

Have you considered having a sheet metal lid?

Not really, I don't fancy that at all.

Dave.

[ecat]

No moulds, they just cut it out from a larger sheet from stock. It's square with 7 holes in it. Probably the simplest thing possible for them.

Sounds to me like the perfect excuse to buy a laser cutter 

[EEVblog]

Sounds to me like the perfect excuse to buy a laser cutter 

An A3 sheet of 2mm clear lexan polycarb is $7.30 on ebay ($4.80 for A4 size).
I could laser cut at least 20 from one A3 sheet, so that's $0.36 ea
Assuming I could get a cheap laser cutter that could handle sheets that size...

Dave.

[MickM]

Hi;
 check this out:


I think it turned out well.

Mick M

[HLA-27b]

Not really, I don't fancy that at all.

Well my idea bag is empty now 

[EEVblog]

Hi;
check this out:
I think it turned out well.

Yes, I do PCB front panels all the time.
I kinda had my heart set on a clear top to see the circuitry for this, but maybe not...

Dave.

[bradleytron]

I think it would be too distracting to have to read this kind of display, what about an LCD with a shift register? There is an article posted in EDN magazine, EDN Access--12.18.97 LCD interface saves mC I/O pin, EDN Staff- December 18, 1997, Robert Wells, ETR, Moab, UT which takes this approach. I checked Digikey and the 74HC164 is selling for around 0.13 cents in 2000 quantities. 

[EEVblog]

I think it would be too distracting to have to read this kind of display, what about an LCD with a shift register?

The choice of LCD has nothing much to do with LCD pins if you use a module instead of segmented display.
It's mostly about cost, mounting etc.
I am liking the module over a segmented version. More info, and possibly cheaper. Just a matter of which one and how to mount it and how to do the front panel.

Dave.

[kfitch42]

Silly question from a 'young player' ... err make that complete newb. Where can you get LEDs for 1 cent each in 1000 quantities (thats what I recall Dave saying in the video)? I checked mouser and digikey... the cheapest I could find was around 4 cents. That is a pretty dramatic difference.

[ovi_mv]

Hi

The displays that i am talking about are spares for the following NOKIA1202, NOKIA1110 and NOKIA1600.
The 1202 has the solderable type connector with SSOP pitch and 0.25mm wide pads - it can be a little tricky for hand soldering but has two 0.8mm alignment holes in the proximity of the pads that can be used for alignment.
The 1110 and 1600 have a hirose DF23-10DS (DF23C-10DS-0.5V(51) - manufacturer part number)  connector.
The 1110 & 1600 have the same pinout configuration and share some of the commands with the remark that 1600 is 4k color enabled.

All the displays work on 3.3V rail, no external negative PS is needed nor any other type of extra components - apart for the .1u cap for the LCD logic
I found the connector on Farnell and Mouser  and the price is about 0.52$ / pcs going down to 0.315$US / 1k. As a separate remark i received a price offer from Converege in february this year and they offered one reel of approx 4200 at 0.27$.pcs.

The drivers for 1110&1202 are available if necessary, the 1600 version is advanced state ongoing project.

As for the uC personally i am a big fan of LPC1114-TQFT33  if you consider the  price for 48MHz,  32K FLASH, 8K RAM is really cheap. For this project LPC 11U14 or 11U13  could be a good candidate. They have a little less RAM but has built in USB connection and USB stack and that can help specially if you want to add USB features (logging, monitoring, pram setting, etc.).
My choice for uC was also motivated by the fact that NXP teamed up with Embedded Artists and CODE RED and produced a very affordable toolchain (HW&SW) for entry level users.

Ovidiu

[EEVblog]

I think it's coming down to either:
Nokia 5110 display 84x48


or a standard 8x2 text display:


The 8x2 text display is about half the cost of the Nokia one.

Snap poll please!

Dave.

[george graves]

Now you're talking!

Even with a little 8x2 or 16x2 display you could can do some fancy stuff with the custom characters.  Like a little slow updating graphical display of the voltage/current history would be interesting.

[Uncle Vernon]

The 8x2 text display is about half the cost of the Nokia one.

Snap poll please!

Dave.

The 8x2 is more in line with the minimalist design you started with, and every cent still count's, so I'll vote for the smaller option.

[lk]

Any of those two displays will work, do the job. And with the nokia one you will even be able to implement the decade display, so everyone wins

-lk

[rr100]

Snap poll please!

I vote for the small one as well, looks to be good enough and then yes, go small and go cheap. I can't imagine the size, I assume it is still readable at let's say 40cm on the bench (assuming reasonable eyesight...)?
How's the power consumption for the backlight (I assume it's LCD backlight...)?

[cyteen]

Standardizing on a more capable display has the advantage of buying in higher volume and being able to reuse excess stock on the next project and it saves on relearning/coding the interface as the same knowledge/libraries can be used. How much is convenience worth to you? At some point penny pinching on the input costs just devalues the final product.

Our russian friends at vrtp make use of the nokia screen for a variety of projects mostly using pic but atmel/arduino libraries are available.

[george graves]

Those cases look nice.  Are they custom or off the shelf?  You wouldn't happen to have a part number?

I've been looking for some cases with a "standard"screen cut out for a while.

[EEVblog]

I vote for the small one as well, looks to be good enough and then yes, go small and go cheap. I can't imagine the size, I assume it is still readable at let's say 40cm on the bench (assuming reasonable eyesight...)?
How's the power consumption for the backlight (I assume it's LCD backlight...)?

The 8x2 has a 4.75mm x 3.95mm font.
The Nokia screen of course can be anything you want. Not sure of it's exact display area.
A pure reflective 8x2 (i.e. no backlight) would almost certainly have better contrast than the nokia which is transflective with backlight.
The 8x2 can have a backlight and transflective too, and I think both take up to 20mA backlight current max.

Dave.

[MickM]

Hi Dave;
  why not put the pads in for both displays?
Maybe have a jumper to choose.

I would prefer the 16x2 HD44780 as I have some.

With your two choices though I pick the Nokia, it's more flexible.

Mick M.

[EEVblog]

Shame that neither of them are suitable for my new low profile Bench PSU case idea. Would have been nice to re-use.

Dave.

[caroper]

I vote 2x8 in the Quick Poll

[hlavac]

The 8x2 can have a backlight and transflective too, and I think both take up to 20mA backlight current max.

Okay, but with that 20mA you can drive the low current LED 7-segment displays with 2.5mA per segment, so whats the point?

[Aldobrandi]

I think it's coming down to either:
Nokia 5110 display 84x48

or a standard 8x2 text display

The 8x2 text display is about half the cost of the Nokia one.

Snap poll please!

Dave.

I also vote for the 8x2.

[hlavac]

That 8x2 will probably be better that the Nokia one

[amspire]

I would go with the Nokia display.

It would be better at showing both the set voltage/current and measured voltage/current at the same time, and also it means that the user guide can be built into the supply - particularly for things like software calibration. Supplies tend to last 20 or 30 years easily, and it is nice if you do not need to try and locate the PDF manual in 20 or 30 years when you need to recalibrate.

[EEVblog]

Okay, but with that 20mA you can drive the low current LED 7-segment displays with 2.5mA per segment, so whats the point?

a) You don't have to drive it at 20mA, it can be lower
b) You don't need to use the backlight at all

Dave.

[HackedFridgeMagnet]

Nokia

[Stephen Hill]

My vote would be for the Nokia.

[rolycat]

My vote is for the Nokia display.

More educational for the audience, and maybe more fun for the engineer.

[adam1213]

I vote for the 8x2 display. The nokia display would likely be overkill with limited benefits.

Independent of the choice of which of these displays I think the USB power supply will be useful.

[EEVblog]

I vote for the 8x2 display. The nokia display would likely be overkill with limited benefits.

I suspect the same. The Nokia would be fun, but essentially overkill.
The choice might eventually come down the physicality of it all though.

Dave.

[SeanB]

8x2 display, enough to use, but not too much, and no temptation to add frills that annoy after a while ( beep on keypress..............).

[G7PSK]

You can get cheaper Dave a 1mm thick by 2050 by 1250 mm can be had at £22.39 from these people I have never bought one offs normally get the pallet but that appears reasonable for small quantity.

[McMonster]

I'm sure the 8x2 display will be more than enough for this project. Does the job and still has some room for displaying some custom stuff if someone is bored enough to mess with a simple PSU firmware.

[ruku]

My vote's for the 8x2 if you've got to do it... but I really like the idea of the LEDs.

Why not do this? Change the display to a bar graph. (We'll say only one LED on at a time.) The default mode is to show current consumption. How often do you need to change the voltage on your power supply? How often do you wonder what the voltage actually is? Most times, after all, I fix it at a constant value. You regain "easy" functionality, and still keep cost and power usage low.

Put a beeper or a latched LED on the system to let the user know when there's an under/over voltage condition. I think that'd be a winner right there!

Also... this still lets you run variable voltage supplies. You just have to hold a button to set the voltage, or something.

Perhaps a decade style system... Four LEDs reading 1/10/100/1000, and then a 0 to 100% graph.

[dcel]

I think it's coming down to:

standard 8x2 text display:


The 8x2 text display is about half the cost of the Nokia one.

Snap poll please!

Dave.

Funny, I have that exact LCD sitting on my keyboard, reflective no backlight.
Now if I can just figure out how to use it.

Its got my vote!

Chris

[Bored@Work]

Funny, I have that exact LCD sitting on my keyboard, reflective no backlight.
Now if I can just figure out how to use it.

Likely http://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller compatible.

For every self-respecting microcontroller there are typically multiple driver implementations out there.

[kolbep]

For the display, how about going retro, and using a Moving Coil Meter. U could have both the V and I on the scale. The Micro can then use PWM to generate the correct voltage needed to move the meter.

P

[rr100]

Not enough resolution especially with such a small scale, quite nasty to calibrate and set up, not able to display both values at the same time, possibly fragile and expensive.

[PedroDiogo]

I vote for the 8x2 display. You could display the voltage and current at the same time and you have space for a simple bar graph with the remaining segment like so:

V:05.00#
I:0.250#

Where # could be a custom character of a bar chart.

[RJSC]

It's a damn shame that the reflective or transflective character LCD's are much more expensive than those crappy white on blue backlight one can find for an euro on ebay.

[dcel]

Funny, I have that exact LCD sitting on my keyboard, reflective no backlight.
Now if I can just figure out how to use it.

Likely http://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller compatible.

For every self-respecting microcontroller there are typically multiple driver implementations out there.

Thank you sir! I did manage to find a datasheet in chinese that has the pin-outs on it.
And I have been to New Haven and d/l'd that datasheet. I didn't think of Wiki.

Thanks
Chris

[Zad]

If I were making it purely as a standalone commercial product, I would go for the 2x8 display. Nokia displays are great for hacking stuff together in 1-offs, but in commercial products, unless they have a separate bezel/mask they look rather naff and something a student would make. The Nokia display also requires a separate socket, whereas the 2x8 uses standard 0.1in header pins.

However, in this instance it isn't quite so simple. It is being aimed at the hacker and Open Hardware market where using a Nokia screen might actually be a selling point, especially if you want to get the design published in a magazine (great advertising).

Do I remember correctly that the local Maker group Dave visited has a laser cutter? I'm sure for a modest fee they would allow you to cut up a load of acrylic sheet. That would make custom marking available at no extra financial cost, just time.

[NiHaoMike]

As for the 500mA vs. 1A/2A part, what about design it to allow extra DC/DC converters to be added? Maybe have a "standard" version that has only one DC/DC converter and a "deluxe" version (or provision for a user upgrade) that has a second DC/DC converter and an isolated FTDI interface.

I really like the idea for the LED display. You could potentially further cut the cost by making it BCD, but then the analog engineers would hate it...

[EEVblog]

As for the 500mA vs. 1A/2A part, what about design it to allow extra DC/DC converters to be added? Maybe have a "standard" version that has only one DC/DC converter and a "deluxe" version (or provision for a user upgrade) that has a second DC/DC converter and an isolated FTDI interface.

It's not that easy. The DC-DC converter changes, the regulator changes, and their associated thermals change. Bigger and more expensive in both cases.

Dave.

[pickle9000]

Hey Dave,

So if I remember correctly you wanted to use a single sided board, tactile switches that extend through the front case.

If you used the 2x8 module then you will already have a sturdy base to work from. If you cut a hole in the pcb big enough for the lcd holder (the aluminum thingy) , slip it in from the back side then that would be pretty clean and keep the entire assy nice and thin. You would need to use a bit of adhesive to ensure that it would be solid. The adhesive would be out of view on the back side of the board, easy to assemble.

I don't know about your component count but I wanna see you spell "BLOG" with some of the components. It would be very novel, hide components and basically I would get a kick out of it. It may also cause premature baldness.

...mike

[EEVblog]

If you used the 2x8 module then you will already have a sturdy base to work from. If you cut a hole in the pcb big enough for the lcd holder (the aluminum thingy) , slip it in from the back side then that would be pretty clean and keep the entire assy nice and thin. You would need to use a bit of adhesive to ensure that it would be solid. The adhesive would be out of view on the back side of the board, easy to assemble.

I considered that, but it would take up a huge chunk of the board space, unless you mount some components between the two PCBs and mount the LCD offset. But even then it's a big chunk gone.
And then there is the problem of connecting the 0.1" header. Can't use through hole if you use the PCB as the front panel like the uCurrent. Not enough room for a SM header I suspect, and you could bodge it with pads and solder paste reflow, but that's nasty.
A better solution for this would likely be those compact 16x2 LCD like I used on my uWatch. At least then you have a flat flex ribbon cable that can be mounted some distance away.

Dave.

[Rutger]

My vote would be for the Nokia display as you can splash the EEVBlog logo when you start it up. Also my guess is that the Nokia display is a lower current display, but that is just a guess. I would buy both and compare the current.

Rutger

[MagFlux]

 Using a 16 x 2 instead of the 8 x 2 might give you more space to have added functionality.
You may think adding such things as over current, finer current resolution(microcurrent), or preset
voltage and current settings to name a few as excessive.
If this is the case then the 8 x 2 display would be a better fit for the case size that you're
contemplating over the larger Nokia.

[ggchab]

The 7 segments LED displays might not be more power hungry than the bar graph if not only displays are multiplexed but also the segments per display. That's easy to do with a microcontroller and most probably still bright enough to be easily readable. I think it's easier and faster to read a number than having to interpret a bar graph. But that's only my opinion.

I discovered your site not that long ago and I really like it 

[Short Circuit]

Been said before, No, doesn't work; muxing is optically equivalent to reducing the current.
Want to keep brightness, then you must increase the current.

[ejeffrey]

Been said before, No, doesn't work; muxing is optically equivalent to reducing the current.
Want to keep brightness, then you must increase the current.

This is not true at all.  A muxed display will look considerably brighter than a steady-state display of the same power.  Your eye is a non-linear detector and detects something between peak brightness and average brightness.  The real behavior is quite complicated, and of course there is a limit to how much you can win.  At a certain point you simply don't have enough photons, but muxing/pulsing can get you a long way.  This is even a nice trick for single indicator LEDs in low power electronics.  If you flash an LED at ~200 Hz with a ~10% duty cycle it will look like it is on steady but have much greater apparent brightness than a constantly lit LED with the same average power.

[george graves]

^That's really interesting actually.  Thanks for that low power tip!  I'll have to remember that one.

I wonder what PWM does to led life?

[free_electron]

there's another effect at play as well. as the led heats up its emission decreases.

so , by pulsing the led you get lots of photons but the die doesnt heat up as much. it heats very shortly , then has a relatively long period to cool down. so by the time the next pulse comes along you are cold enough to have a gain lots of photons.

so a pulsed led emits more photons than a constant on one  . there are led controllers that run a fixed current to keep the led at low heat while still having emission and then spike short pulses that do not casue noticable heat increase but pump up the emission of the led.

[Psi]

That's what i said on page 1
This thread has come full circle.

There's only so far you can trick the human eye before it starts to notice the brightness dip 

[HackedFridgeMagnet]

If you flash an LED at ~200 Hz with a ~10% duty cycle it will look like it is on steady but have much greater apparent brightness than a constantly lit LED with the same average power.

Can you guys quantify this, or point me to somewhere where they do quantify this. I wonder if it's worth incorporating the effect into a design.

[mathk]

Donno if the idea have been propose and I don't want to read the entire thread so here is my proposition to improve the  Dave's Decade Digit Display.
Instead of having the figure print on the slick screen you can have a reverse silk screen print on a "transparent pcb" for each led. So each led get his own figure. I don't know if that is doable or not (to have a transparent pcb) but that just an idea.

[MikeK]

I wonder what PWM does to led life?

Probably no effect, as long as you're below the spec'd current.

[tom66]

Dave - how about a display like this? http://www.ebay.co.uk/itm/0-96-128x64-OLED-LCD-LED-Display-Module-white-/221030175657?pt=LH_DefaultDomain_0&hash=item33766cd3a9

Pretty pricey for one - but you see those cheap OLEDs in a lot of products. So they must be available cheaper somewhere else. Then again, I wouldn't mind paying a little extra to have a cool OLED display.

[george graves]

I totally forgot about those.  They would bake an excellent display for a PS - but I think dave is going for something a bit more minimal.

[EEVblog]

Yes, I want something pretty minimal I think.
The other battery powered PSU is a better bet for a big graphical display if desired.
Do those OLEDs work outdoors?
(think Agilent OLED meter)

I found a source for low-ish cost 5W isolated converter (still much more expensive than the 2W though), and am now considering a 1A upgrade option, but the cost is rapidly increasing on this project way above what was originally intended.
I know everyone says, "I'll gladly pay X extra for X feature", but it's getting out of hand for such an ultimately fairly limited USB power supply.
So I think a better display and the extra power capability are mutually exclusive. I need the reign in the cost whilst trying to give maximum capability.

Dave.

[caroper]

The original spec was fine.


a) Low Cost
b) Isolated


if it is isolated then 2 in series/parallel  == More current || More Voltage || Split Rail


PC control / display, whilst nice to have is a pure luxury driven by the fact that it is connected to USB, I think the ability to use it with a USB Charger is more useful.


Personally I think any display is overkill if it pushes the price up, it is a field PSU, think battery substitute, use a DMM to set voltage and current and have LED's to indicate status.


To be honest I am not sure where you make the split between the USB uSupply and the battery uSupply but the discussions seam to be merging into one.


You could even start adding the Reference capability that Richards Design is heading towards, but that again is going to far off track (for your project that is, I do like Richards design too).


Follow the advise you gave in today's walkabout, keep the cost down, the spec reasonable and meet the functional goals.


But above all else, keep up the Dialogue, it is entertaining and educational.


Cheers
Chris

[ejeffrey]

So I think a better display and the extra power capability are mutually exclusive. I need the reign in the cost whilst trying to give maximum capability.

I think a better UI is more important than more power.  A device that is inconvenient to use will never be used.  That could be either in the form of an LCD display or an isolated computer interface.  The computer interface provides more features (multiple displays, logging), but is still somewhat inconvenient and can't be used when powered from a cell phone charger.  Still, I would be probably be willing to fall back on the bargraph display as a last-resort option, as long as the computer interface is available if needed.  The LCD provides less functionality, but it always works.  The LCD also requires less development effort on the software side...

[tom66]

Yes, I want something pretty minimal I think.
The other battery powered PSU is a better bet for a big graphical display if desired.
Do those OLEDs work outdoors?
(think Agilent OLED meter)

I found a source for low-ish cost 5W isolated converter (still much more expensive than the 2W though), and am now considering a 1A upgrade option, but the cost is rapidly increasing on this project way above what was originally intended.
I know everyone says, "I'll gladly pay X extra for X feature", but it's getting out of hand for such an ultimately fairly limited USB power supply.
So I think a better display and the extra power capability are mutually exclusive. I need the reign in the cost whilst trying to give maximum capability.

Dave.

There's still the option of designing your own; I know you don't want to mess around with it, but there's a lot to be considered in such a design (so great for beginners) and it will ultimately cost far less than a DC-DC module. You can then also add a tracking pre-regulator automatically to it because the feedback control is freed up. If you use a decent LC output filter, you can make a truly variable ~0.5V - 10V switching PSU with ~10mVp-p noise - no need for an LT3080 regulator. 10mVp-p is likely fine for the target market - I imagine small MCU boards being a common load. (You'll still need a separate isolated 5V though if you go for this; but a 0.5W DC-DC converter is a cheap and readily available component and that could easily power an OLED/LED display and micro.)

[amspire]

There's still the option of designing your own; I know you don't want to mess around with it, but there's a lot to be considered in such a design (so great for beginners) and it will ultimately cost far less than a DC-DC module.

I started down this track with a DC-DC converter for my General Purpose power supply design, and I found myself enormously frustrated. For a start, it is almost impossible to find a source of the right cores with the right material, right gap, right former and right mounting hardware at a decent price for an open source-type design. The builder would also need to get the right gauges of enameled copper wire, the right tape, and then if they do not build the transformer perfectly, it can ruin both the performance and the safety. A poorly constructed switching transformer can easily result in the supply just destroying itself after a few minutes.

The amount of design involved in a  good isolated supply can be an order of magnitude more then a boost or buck converter. When I have done it in the past, it is not hard to end up with about 30 different transformer designs before I get an optimized design I am happy with. An isolated switching DC-DC converter usually works on the bench the first time you power it up, but to get the right power/input/output voltage ranges, the right efficiency, the right noise performance, the right level of switching transients due to the winding leakage inductance, etc is a job that can take weeks or more.

Even more frustrating is seeing the modern core types that could give a much smaller, and much better shielded transformer, except the cores are unavailable if you are not ordering quantities well into the thousands per month. In many cases, the moderns cores require custom pre-formed windings made from flat rectangular-profile enameled copper wire. Impossible for the hobbyist.

All this means that if you try and design an open source isolated DC-DC converter, you are likely to end up in the transformer manufacturing and supply business. As there is safety isolation involved, this can easily be a task you want to avoid.

If you go down the track of using an off-the-shelf transformer, the reliable supply of cheap transformers is pitiful,  they are usually very poorly specified (so you have to get them and test them to see if they may work as required) and never exactly what you need. I found that to get the performance I needed, instead of going for a custom 10mm core design, I had to choose a 25mm footprint transformer that was way to big for any compact case. You can be lucky, but usually not.

The DC-DC converter module is just a more practical way to go, and for most people, it ends up being a cheaper option.

Richard.

[EEVblog]

The DC-DC converter module is just a more practical way to go, and for most people, it ends up being a cheaper option.

I was not silly enough to consider anything else!
The modules are by no means perfect, but you simply work around their limitations.

Dave.

[ftransform]

how about you control the voltage by adjusting the brightness and blinking a single LED. You could have a little printed reference table to judge what voltage it is outputting and how fast it is blinking. I just saved you a $, I expect 50% royalty. MAYBE a multicolored LED if you wanna get fancy but jesus we are not made of money man.

I was going to suggest a little speaker to read the voltage out loud but that might be too expensive. You could corner the blind market.

[rbk17c]

I have now finished a one off PCB with 26, 1206 SMD leds arranged as:
01
01234567890 ss
01234567890 ss
(a 200 count display)

Its 2 sided, 100X39mm PCB, in a charlieplexer arrangement (28 leds, using only 6 cpu-pins).
while it works, and the display is quite stable, I must confess that it is extremely hard to read.
I even added some 'back light' (switch on all Leds for something like 1/100 of the time), AND changed the colors, I still find myself counting.:-(
This is almost as geeky and hard to use as a BCD clock. - Sure - after 1/2year of frying your projects, you WILL learn to read it fast and precise, but...
I might still be saved by some clever front panel, but for now...

/holger






 

[bookaboo]

I think it's coming down to either:
Nokia 5110 display 84x48


or a standard 8x2 text display:


The 8x2 text display is about half the cost of the Nokia one.

Snap poll please!

Dave.

Wow the nokia one wins on so many levels.

- It will look good so more sales (if thats the goal)
- You can do whatever you want with bargraphs etc,
- Fantastic learning for everyone

[MickM]

Hi;   
   My vote is for the Nokia display.
Adafruit has them back in stock.

Mick M

[calin]

I reckon I did not had the time to read the whole thread so if this idea came up please disregard.

This is an "USB power supply" right? supposed to be hooked by a laptop or PC. So ... you have one BIG DISPLAY right there. Having a device implement USB is not that hard and does not require a super hefty MCU; and a simple application that sets and displays the voltage and amps is theoretically "free". Plus you can have adjust both ways, made from the PC side and/or using keys/encoder etc on the supply itself.

Sincerely, I find this solution while not as fancy as a LCD display cheaper and practical. Plus I am 100% sure that USB communication will not use up any significant power.

Just a thought.

And yes, Dave no need to get it fancy; isolated and normal power. Display ca be made of a nice app on the PC and done.

[Rufus]

Been said before, No, doesn't work; muxing is optically equivalent to reducing the current.
Want to keep brightness, then you must increase the current.

This is not true at all.  A muxed display will look considerably brighter than a steady-state display of the same power. 

Don Klipstein http://donklipstein.com/ledp.html doesn't think so.

  I have done lots of experimentation with 555 oscillators and various LEDs and solar cells in various room lighting conditions. Regardless of frequency and duty cycle, a pulsed LED that gives the same solar cell response as a continuously operated one of the same model will almost always match the visually apparent brightness of the continuously operated one. I have sometimes seen slight gains - less than 10 percent when I get any gain at all - in apparent brightness if the pulse frequency is barely fast enough to make the LED not visibly flicker. This frequency is usually around 60 Hz.

I haven't seen anything but an ancient HP application note claiming otherwise. LED efficiency usually drops off at higher currents and I^2R losses mean pulsing the same average current results in higher die temperature.

[SteveyG]

Been said before, No, doesn't work; muxing is optically equivalent to reducing the current.
Want to keep brightness, then you must increase the current.

This is not true at all.  A muxed display will look considerably brighter than a steady-state display of the same power. 

Don Klipstein http://donklipstein.com/ledp.html doesn't think so.

Who the F is Don Klipstein and why should we care about his opinion? There's lots of literature out there showing how the eye responds to certain frequencies differently, which has the effect of making an LED driven at a low duty cycle at these frequencies to appear brighter than an LED driven with an equivalent average current. The wavelength of the LED is also important. Just because 'Don Klipstein' dicked around with a 555 timer and an LED doesn't make it gospel.

I haven't seen anything but an ancient HP application note claiming otherwise. LED efficiency usually drops off at higher currents and I^2R losses mean pulsing the same average current results in higher die temperature.

I²R losses on a non ohmic conductor?



You can get 3 digit 7 seg displays for 38 pence from Rapid in the UK. These would be ideal IMO.

[george graves]

Here's a nice set up if you wanted to keep the design all pick and place-able.




Taken from: http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=4436&p=43546#p43520

[Zad]

The issue isn't the cost of a 7-segment LED array, but the current. Imagine 3.88V at 88.88mA. That is 96 illuminated LEDs. Even at 1mA each, it is a lot of power overhead.

[poptones]

I'm new here so my opinion counts squat, but I like the idea of the PC enabled power supply. Why not make it usb enabled? Not only does this make it easy to handle the settings and display, but you could even use software to operate it as a data logger! Make a circuit and see how it performs over a range of voltages easy peasy. To me, this would make it considerably more valuable than a small box with some numbers and buttons that just happens to use my very expensive pc as a mere source of current.

[McMonster]

As someone probably mentioned already, the problem would be in carrying the signals over the isolation barrier. There are chips that can do that, but they're expensive.

[poptones]

OK, what about this? Rememebr the old BCD thumbwheels? THese provide a readout and provide a means to set values. So what about making a modern LED version of the thumbwheel? Use the strings of LEDs, but provide an up and down button for each decade. Then you're not just turning a knob and counting the dots in your head - if you want to go up by a tenth of a volt, you press the tenth of a volt setting. No need to count as your brain instantly associates the button press with the led change to be a tenth of a volt. If you want to go up a volt, go up a volt. etc. Put white lines on the panel to give quick association with certain common levels like 3v, 5v, 12v, 15v, 24v etc.

[sonicj]

source: decadecounter.com

[andyturk]

@sonicj: I loved using those as a kid, and drove them with 7448s. Even got pretty good at reading hex values using the weird segment combinations created by the 7448. 

[Zad]

I had to post this. Your photo reminded me and I had to go and look for them! I bought them when I was a kid, in a box of mixed 7-segment displays from Tandy. This would be around 1980 I think. They were great for messing around on the breadboard. Good times!

[EEVblog]

I probably still have some of those in a draw somewhere...

Dave.

[poptones]

LOL gonna go retro? Make a version with nixies for those who want some nostalgia with their USB power supply?

Oh, I do have a question: regarding the current capabilities of this thing - why not have it battery powered and charged by usb? One could run much more instantaneous current, you'd have a better power budget, and it would generally be a more flexible device - like a battery with adjustable output and current limiting.

[Pilot3514]

Dave,

I give you full marks for creativity but I can not score this a easily usable.

As with so much in design, you have trade-offs.  Power consumption, cost, availability, size, weight, and so on.  On your scale, you balanced everything and came up with this solution.  No one can fault you for that.  Someone else will weigh the factor different and find a different balance point.

When I see this design, I see something in the computer bag or I have a computer near by.  Therefore, I see computer control as a valuable option.  Therefore, having another display (DDDD) is a viable secondary alternative.  It function as both computer controlled and stand-alone.

[Dan Budd]

G-Day mate!  (Trying to speak the local language. Hope I did it right!)

I have enjoyed watching your video blogs.  I have been watching them in order (skipping over the one's I'm not interested in) and have arrived at #298.

Question:  In this blog, you are selecting the size of the enclosure.  How do you engineer a solution to the chicken and egg problem?  The size of the enclosure is determined by the size of the board. The size of the board determines the size of the enclosure (mounting holes to match mounting bosses).  Given a schematic of parts, how do you select the size of the box?

Another question/suggestion:  You also make reference to selecting your micro controller based on driving six 7 segment displays directly from the processor. That's a lot of I/O.  At the risk of offending your parts budget (and adding to your parts count), would using an I2C LED driver such as AS1115-BSST to handle the display help?