The revision 4.1 boards have arrived today, and the new watch has been assembled. I’m happy to say that this revision works! So far only a small portion of the code has been implemented to just test the components onboard but for the moment everything seems to be working!

There were some difficulties in assembling the board. Two boards were assembled, the first one had a defect that I couldn’t exactly track down, on my first assembly attempt I found that there was something shorting the EN pin to ground, this prevented the ESP32 from booting up. I removed all components attached to the EN pin and found a 30 ohm short to ground and there was nothing visible causing the problem (I can only assume there was some defect causing a via to connect to ground but couldn’t find exactly where that short was happening). After an hour or two of trying to fix that issue I cut my losses and just assembled a second board which is running the watch in the above image.  

Currently the code I have running simply boots up the display and shows some of the readouts from the battery monitor IC (MAX17260) then puts the device to sleep. For the moment everything seems to be working, the ESP32 can communicate with the two I2C devices on board (battery monitor and touch controller) and best of all the LCD works!

With all that said I’ve found a small error in this version that I’ll have to fix. Currently the battery monitor can’t see the charge current since the charging IC connects directly to the battery without going through the sense resistor. This causes the battery monitor to not see the device as charging, the result is that the battery percentage doesn’t increase when charging.

I’ve also made some modifications to the case design. The case is no longer held together by screws, instead the strap holder was created from some pieces of 24-gauge steel wire. The advantage to this design is that the watch can use any 24mm (or smaller) watch strap bought online. This solution makes the watch easy to assemble and disassemble with just a pair of pliers and strengthens the overall watch body.

Overall the project is on the right track now, and this revision of the board will work perfectly for developing software. I’m still planning on doing a revision 5 which will just be a pass on the layout to compact the design as much as possible.  

See you in the next log!