Zapped Circuit Boards

After AMOS had been on its own for 5 days, I drove out to pick it up so that it would be safe from Hurricane Dorian and so that I could modify the power cable for the cellular hotspot to be software controlled (i.e. shut off whenever AMOS goes into sleep mode).

Although it had a low battery and was too weak to extract itself from some branches near the shore, it appeared to be working normally when I picked it up. So I unplugged the power cables inside the battery box, loaded it into the van, and drove home. After I got home however, it would no longer boot up properly, even after the battery was sufficiently charged. A few hours of hardware troubleshooting revealed that the short-range wireless module was somehow short-circuited, and drawing too much power. Also, the 3.3 V regulator on the Raspberry Pi mainboard was only putting out about 2.6 V. Replacing the regulator with a different one didn't seem to help either, i.e. the Pi board would still not boot up. 

Later that same day, I drove the van to Kirsten's cross country practice to pick her up. While waiting in the parking lot for 10 minutes, the van's battery mysteriously died, and could no longer be started when the practice ended. Turned out the alternator was shot and needed to be replaced, so overall not a great day for electronics. Maybe I was emanating some weird electromagnetic radiation or something that day. Actually I think what probably happened with AMOS was that when I unplugged the power cable in the battery box and transported it in the van, it probably shorted out on the +12 V battery terminal, destroying both the Pi board and the wireless transceiver.

Turns out it's not all bad though. I had been contemplating switching the Raspberry Pi Compute module for the smaller, less expensive Raspberry Pi 3B+. The 3B+ actually has a slightly faster processor than the compute module, built in WiFi and Bluetooth, and 4 USB ports all included, whereas the Compute module only has one USB port, and requires a separate hub to add WiFi and Bluetooth functionality. Originally I had gotten the Compute module because it had two camera ports, and might make 3D ranging possible using stereovision. Turns out it's way easier to do that with LiDAR though, so no real need for two visual cameras. The 3B+ has fewer I/O ports too, but it still has way more than AMOS needs right now; about 13 extra digital I/O pins are still available for any new functionality. 

Here is a comparison shot showing the reduction in size between the Compute module and the 3B+:

The next few days are going to be spent setting up the 3B+ and the replacement wireless module. The software changes are pretty minimal, just pin re-numbering mostly. Most of the time will be spent setting up the software, as I don't have a workable image ready for this board yet, plus a bit of time for soldering together the replacement wireless module.