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

[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!