Friday, April 14, 2017

Simple Led Nameplates for coworkers -- Kicad/PL9823/Atmega8/Arduino/NeoPixel /w github

This was a quickie that came out really cool...

I designed this project around parts I have mass quantities of... Mainly leftovers from other projects. This kind of thing is a great way to pare down your parts hoard!  This why the PCB is a mishmash of odd components... I have a crap load of ATMega8 PDIP package chips... like seriously 300 or so of them. (Dont ask)  So I tend to use them everywhere.
I designed these around prototype service which is 10 boards 10x10cm for around 16 bucks. This means my friends get one sign and about 9 personalized coasters ;-)

 In kicad I simply plopped my prebuilt ATMega8 MCU board sck file as a hierarchical sheet then broke out nets for the brightness knob analog input, button input and PL9823 pixel data output (A ws2812 compatible in a 8MM T package LED... I LOVE These things!).

Using 12 of these PL9823 8mm devices is way overkill but you can control the brightness with the pot, I didn't really know how it would cast through the PCB so I figured better to be too bright than too dim.  It sure is pretty though.  I do the fronts in 1.2mm thickness and the back in 1.6mm.
 I put the footprint for two POTs since i have lots of both. Also my original ATMega board needed timekeeping it had footprints for crystal oscillator, this design didn't so I did not populate the crystal and even left out some of the bulk and bypass caps... simply not needed.

The pixels are arranged in a string of course, and I added headers for the input and output data... This way I can chain them to another neopixel board or another one of these that simply does not have the MCU populated.  With things like this I try to make the boards are re-usable as possible.  Adding extra footprints is free!

The whole design took a couple hours since I was re-using huge parts of previous designs. If i had it all to do again I probably would have added a serial header to allow easier re-programming. As it is, I am using an ISP programmer which most people will not have on hand. But this was a carry over from the reused block.  If i had done that, this board would look like a Arduino UNO in the Arduino UI. But oh well, that will be V2.5 I guess...

For the logos and graphics i used KiCad's Bitmap2Component and put them on the solder mask layer.  The front has most of the solder mask removed on the back and selectively removed on the front.  This combined with copper layers determines where and how the light passes through the PCB.  The red soldermask completely absorbs some wavelengths of light while the fiberglass PCB transmits everything. So you get a great alternating effect as a given color reacts to the different materials. You really have lots of options to get some cool effects.

I have posted all the design files and code to github.  Links below! Enjoy!