Hi all,

We've slowly been working on the design, Dmitry is soldering the PCB's as we speak (or type since this is an article, english is weird). He'll probably have an update with some pictures soon!

The good part about working with hardware is that we find issues quickly. I found out that the ATTiny85 doesn't have internal pull-up resistors on its pins! Woops, big oversight on my part. Our initial boards won't have i2c working due to this but we can jerry rig a solution for now. We'll be adding in 10K Ohm resistors as pull-ups. We may also add pull-up resistors to the buttons as well, though this hasn't been drawn out yet. The updated circuit diagram can be seen below:

This also means we have updated parts list:

• https://www.digikey.com/en/products/detail/microchip-technology/ATTINY85-20PU/735469
• https://www.digikey.com/en/products/detail/vishay-semiconductor-opto-division/TSOP58238/4695679
• https://www.digikey.com/en/products/detail/vishay-semiconductor-opto-division/TSAL6102UL/20379899
• https://www.digikey.com/en/products/detail/kemet/C320C104K5R5TA7303/3726160
• https://www.digikey.com/en/products/detail/yageo/MFR-25FBF52-97R6/12793
• https://www.digikey.com/en/products/detail/cui-devices/TS02-66-50-BK-260-LCR-D/15634249
• https://www.digikey.com/en/products/detail/yageo/MFR-25FRF52-10K/14626

Speaking of updated parts list, I've also found all of the parts for the SMD version of the board! No PCB design yet since we're still testing the initial through-hole design but thought these might be interesting to look at. The SMD parts list is here:

• https://www.digikey.com/en/products/detail/microchip-technology/ATTINY85-20SUR/2357441
• https://www.digikey.com/en/products/detail/vishay-semiconductor-opto-division/TSOP75338TR/4695863
• https://www.digikey.com/en/products/detail/harvatek-corporation/B2571IR-A1C000272U1930/13574173
• https://www.digikey.com/en/products/detail/murata-electronics/GRM02YR60J104ME01L/16033687
• https://www.digikey.com/en/products/detail/stackpole-electronics-inc/RMCF0805FT100R/1760711
• https://www.digikey.com/en/products/detail/c-k/PTS-647-SN50-SMTR2-LFS/9649857
• https://www.digikey.com/en/products/detail/yageo/RC1206FR-0710KL/728483