Author Topic: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3  (Read 54779 times)

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Offline dh

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #75 on: June 26, 2012, 01:45:31 pm »
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!
« Last Edit: June 26, 2012, 04:14:08 pm by dh »
 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #76 on: June 26, 2012, 01:45:52 pm »
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.

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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.

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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...

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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.
« Last Edit: June 26, 2012, 01:48:23 pm by EEVblog »
 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #77 on: June 26, 2012, 01:56:24 pm »
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?

 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #78 on: June 26, 2012, 02:06:30 pm »
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.

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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.
 

Offline PeteInTexas

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #79 on: June 26, 2012, 02:13:07 pm »
I don't like it. All that solder is sure to add to the overall weight of the device.  ;D

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.
 

Offline dolabra

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #80 on: June 26, 2012, 02:14:21 pm »
How about combining a cap-touch slider and a bar graph?  that might be a neat effect to increase and decrease values?
 

Offline Zad

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #81 on: June 26, 2012, 02:16:27 pm »
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,

« Last Edit: June 26, 2012, 02:18:35 pm by Zad »
 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #82 on: June 26, 2012, 02:21:02 pm »
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.

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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.
 

Offline Zad

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #83 on: June 26, 2012, 02:22:51 pm »
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.


Offline Mercator

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #84 on: June 26, 2012, 02:41:00 pm »
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.

« Last Edit: June 26, 2012, 02:51:45 pm by Mercator »
 

Offline notsob

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #85 on: June 26, 2012, 02:49:52 pm »
If you use a clock face start 1 at 1 o'oclock - so us old farts can read it without thinking
 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #86 on: June 26, 2012, 03:04:05 pm »
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.

Quote
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.
 

Offline Psi

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #87 on: June 26, 2012, 03:10:56 pm »
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.
« Last Edit: June 26, 2012, 03:17:37 pm by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline m12lrpv

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #88 on: June 26, 2012, 03:38:06 pm »
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.
 

Offline TerminalJack505

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #89 on: June 26, 2012, 04:31:32 pm »
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.
 

Offline dda

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #90 on: June 26, 2012, 04:37:59 pm »
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.
 

Offline dh

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #91 on: June 26, 2012, 04:45:59 pm »
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.
 

Offline LEECH666

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #92 on: June 26, 2012, 05:13:29 pm »
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).
 

Offline HackedFridgeMagnet

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #93 on: June 26, 2012, 05:14:29 pm »
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.

 

Offline lk

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #94 on: June 26, 2012, 05:47:22 pm »

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.  ;D

-lk
 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #95 on: June 26, 2012, 06:07:44 pm »
ps. I don't like the case much, prefer a flat bottom.

I have yet to find a suitable practical alternative unfortunately.

Dave.
 

Offline amspire

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #96 on: June 26, 2012, 06:08:29 pm »
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.
 

Offline robbyn

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #97 on: June 26, 2012, 06:10:32 pm »
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.
 

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #98 on: June 26, 2012, 06:27:50 pm »
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.
 

Offline cheepokleebo

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Re: EEVblog #298 - Dave's Decade Digit Display - USB Supply Part 3
« Reply #99 on: June 26, 2012, 07:27:34 pm »
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   
 


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