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

Part 3 of the USB Power Supply design.
A low cost 4 digit LED display solution = Dave's Decade Digit Display
Is it a triumph of novel idea over practicality perhaps?

[lacombar]

Design rule #1: never put an engineer in charge of the UI design.

Thanks to prove that rule.

[ChartreuseKitsune]

Something you could do to make it more readable would be to a plastic overlay over it so that the leds would illuminate through a mask of the number they represent. I can't imagine it would keep it below the cost of 7 segment module though, but would keep the power down.

[Niksan]

I'll also add that you normally harp on about UI and whatnot, so this must be a windup. ;)

[absurdengineering]

This display idea was IMHO the classic penny wise/pound foolish trade off. I’d like both nice knobs and a readable display, and would gladly pay for that. The knobs can lay flat on the other side of the board, opposing the banana jacks. All those cost cutting measures are turning a good idea into a piece of junk…

[TheSageDad]

I think this is a cool idea and hits many points of good design. Anyone who would actually use this product should appreciate the engineering process...

[insonicbloom]

I love that solution, obviously not on a full bench supply, but for a portable usb bench supply that has to be one of the best ideas for displaying voltage at low cost/current use - just make sure they are aren't the ones that blind you when you turn them on

[lukearoo]

though impressive, i dont revere this as being to practical, if i had any need for this device i think a cost increase of a few dollars for an easily read display is almost essential, i would have to spend more time checking / working out what the voltage and mA i am about to put through whatever i have hooked up to the device,

[mikeselectricstuff]

Another issue could be the lack of strong visual cues to tell you how far up or down the scale you are - you'd need to see the ends to get the position, which may be hard in darker conditions. Maybe an answer would be to have all LEDs on really really dim to give better contextual information.

[EEVblog]

You are missing the whole point about the extra cost, size, and power dissipation required in the isolated converter (and following circuitry). It's got nothing to do with being able to extract extra current from the USB port using various means.

[HennerZeller]

Well, Dave, I think you found a cheap solution, granted. You outdid yourself in lowering the component cost.

I do think, however, that the potential user will be happy to pay $2 more for a useful display :)

For the sake of educational value and figuring out mass production practicability, it might actually be interesting to consider the self-made 7-segment displays with slots in the board (which then have to be filled with some kind of resin I presume). Pro: More multiplexing control and flat.

[WhitentonMike]

Absolutely. My point exactly. Toss the display. Anyone buying this device will have a DMM that can be used to set the current. The point is "constant current" so it should be a set-it-and-forget-it device. The only thing I "might" add is a warning LED if the current drifts beyond a predetermined amount. Just as a heads up.

[EEVblog]

I can't imagine a huge difference between a 7 seg display flickering 4.99-5.01 and this display flickering the same. Yes, it's probably needs real-world prototyping. It's just an idea at this stage.

[GadgetAddict]

Pretty awful for the user. I'm pretty sure that display would piss me off if I had to use it for any real amount of time. I'd rather buy something decent than save a couple bucks.

[DamacusSquared]

That's funny while watching this I had a similar idea only using the decade bar graphs but I like this idea. It's easier to customize than my idea. Beautiful work. Love it

[mikeselectricstuff]

May be OK for setting values but for measuring I think it will totally suck ass - you'd need to damp it a lot to avoid jitter, making it less useful.. A small cluster of LEDs in seven-seg format would be better. If you go with red you can use series pairs for extra length and brightness without more current. Low-current LEDs behind a red tint filter would draw maybe 8-10mA for 6 digits - not a lot from your 500mA available.
You really need to prototype it to see how well it works in practice.

[azyfloof]

Interesting display solution! How about arranging the LEDs in concentric rings, like the hands on an analogue clock, or have each digit group arranged in a circle like the dials on a electricity meter?

[voltareamstereo]

What about using the rectangle led's (as used in LED bar graphs) laid out in a 7 segment configuration
It's kind of old school but could work

[jjoster]

The way I understand the spec, that 500mA is the maximum you can guarantee to be delivered over the wire from a standard outlet. What actually can be consumed is a factor of the impedance of the load. Since this is a electronics tool it seems reasonable to leave that impedance in the hands of the tools user.

[timb]

I like it Dave! I like that there are labels on the silkscreen, it makes it more readable. :)

[turtletaub-ft]

I really like the solution, elegant and funky and shouldn't be too hard to see.