Charles Jr

A Hardware challenge.

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I was surprised when I found out that OSHPark's minimum board size is 0.25x0x25 inches.

So, I tried to make something useful of that size.

Here it is.

This is a 3-pin charlieplexing board, so that makes n^2 - n = 6 LEDs.

This board makes use of the smallest size on OSHPark, which is 0.25x0.25 inches.

That's ¢30, delivered. (Please order more than that, though! OSHPark deserves your support ;) )

It uses 0603 LEDs and Resistors (for red LEDs, I'm using 75 Ohm. Remember to halve the resistance because of charlieplexing --> two resistors in series with LED in between!)

A reel of 100 0603 LEDs can be found on Ebay for $4. The resistors cost me $1 for 100.

Oh, both of those have free shipping.

So, these things have a per-unit cost (without headers) of ¢10 + ¢24 + ¢3 = ¢37.

That's pretty good, right?

  • Ordering Information

    alpha_ninja09/22/2015 at 04:07 0 comments

    I just realized I never uploaded any information on ordering these boards, so here it is:

    You can find the board at

    You can also find the design files in the github repo.

    That's all, folks!

    P.S. I'd like to ask that you order a few dollars' worth at least from OSHPark: The shipping may be free to you, but it isn't to them!

  • Library uploaded.

    alpha_ninja05/30/2015 at 20:55 0 comments

    Not much to say here, but the arduino library has been uploaded to the github repository.

    I haven't yet changed the code to work with LEDs soldered differently from mine — I'll try to do that later today though.

  • Arrival & Assembly & Awesome

    alpha_ninja05/30/2015 at 15:24 0 comments

    Last Tuesday, 15 of these arrived.

    Yeah, I'll need to redo the silkscreen—OSHPark understandably couldn't handle those tiny letters—but testing showed all the traces worked, even that one that's really close to the PCB edge.

    So, I assembled two of them.

    While assembling, I tested them with the multimeter—it turns out it's really hard to keep track of which LED is oriented in what direction.

    Also, 0603s are generally quite annoying.

    A quick test on a breadboard showed they worked great—so I went to the arduino and started coding.

    After some initial tests with port manipulation, I started writing a library. It's done and working, and I'll upload the code when I add some more comments ;)

    EDIT 1: the board files have been changed to improve the silkscreen & increase track width— see github. Yes, the gerbers have also been updated :)

  • Changed design

    alpha_ninja05/14/2015 at 02:31 0 comments

    I changed the design, getting rid of castellated holes and fixing a mistake I had in which one LED was going in the wrong direction.

    Here's the old screenshots - I will be removing them from the gallery.

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davedarko wrote 05/30/2015 at 19:11 point

A fan of tiny OSHPark boards and charlieplexing? Awesome, me too! Nice job!

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alpha_ninja wrote 05/30/2015 at 19:13 point

Thanks! The gerber zip (all ready for OSHPark) is on the github page and I'll upload the Arduino library soon (might work on attinys too, but not sure). I'll also change the silkscreen a bit :P

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davedarko wrote 05/30/2015 at 19:23 point

I'm more a 1206 guy :D I've used some duo-leds with charlieplexing, that was fun. and also made some boards with a bargraph display and a attiny onboard, which you can see here 

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alpha_ninja wrote 05/30/2015 at 19:35 point

That's understandable, but I wanted to hit the lower OSHPark limit ;). Those projects look really nice—do those duo LEDs use the two contacts to change color based on polarity or how do they work?

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davedarko wrote 05/30/2015 at 19:43 point

yes they do. I was able to get three colors out of them :)  (yes, that's Tuvok in the background)

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alpha_ninja wrote 05/30/2015 at 19:45 point

Sweet! that in a smd package would be neat...

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davedarko wrote 05/30/2015 at 19:54 point

they'll probably be all 4 legged in smd.

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