I built a simple Wi-Fi thermometer to monitor the temperature of a Hotbin. It uses and ESP32 and sends the data to Prometheus for storage. It's not uncommon for there to be gaps in the data because it is entirely solar-powered. Especially so in the winter months.

Recently there was an unusually long gap. Over a week went by with no data. That included some days which I was sure had enough sun to wake it up. I plugged it into a serial monitor to see what was going on. I always leave useful Serial.print() calls in my code for exactly this kind of thing. It showed:

Connecting to WiFi.......... FAILED!

I assumed interference was to blame. I'd recently had to change my Wi-Fi channel because my neighbour had set up a new AP on the same channel as me. I moved the ESP right next to my router... Same failure.

This was really weird. It had worked perfectly for nearly 3 years.

I wondered if there had been a random bit flip or some kind of firmware corruption, but I would expect that to have caused a fatal error, rather than a Wi-Fi timeout. I wanted to dump the firmware to compare it to the original, but I couldn't find any way of recovering a readable firmware dump.

Reflashing the firmware fixed whatever the issue was 🤷