(October 2015)

Over 5 weeks from the original shipping notification, I finally have gotten the WS2812s. Turns out the shipper shipped them China Post, when I paid for the upgrade to China DHL. It also turns out that AliExpress has a clause for unilateral changes to shipping method. Over 2 weeks of dispute resolution process later, and AliExpress forced the seller to refund the whole shipping cost. As a result, I got 300 LEDs for $13, shipped. I wouldn't recommend seeking to replicate these results, but being able to quote the rules and having screenshots to prove everything was quite handy. I'm only 2 months behind schedule now!

Now that I have some LEDs, time to get them attached to the waiting board. I had tested out the back side, and made sure all the power supplies were working (after some troubleshooting). I got the first board together and tried to test it. The color LEDs were fine, but I simply could not get the voltage for the IR LEDs and the Shift registers (separately adjustable) to reliably trigger when the IR sensors were touched. I was counting on this particular flavor of shift register to have the threshold voltages on thee inputs adjust with Vcc. They do, but the analog circuitry of the phototransistor just couldn't provide enough swing to work nicely.

I decided in the end that I would use an opamp/comparator on each phototransistor, with a global 10k pot to set the threshold on all 25 sensors (per board). I looked at various other methods and part costs, and couldn't find much cheaper than a LM339. I was not looking forward to bodging on 7 TSSOP-14 ICs dead bug style, so a new PCB rev would be needed. I hadn't used up many parts on the first boards yet, so I was able to get away with only ordering the LM339s and some more passives to keep my options open on the phototransistor pullups.

The second rev boards had the added LM339s, and removed the shift register variable power supply. I kept the adjustment for the IR power supply for brightness control, and a 10K pot was added for the IR threshold level. DirtyPCBs came through again with fast turnaround and DHL shipping to get me going before the end of October.