The V1 prototype attempted to neatly package up the V0 prototype. I 3D printed a case out of ABS plastic to mount it to the water meter. The strap was printed using TPU which is a flexible material.

I switched to the more capable ESP32-S2 to allow me to remove the Arduino and combine all of the processing on one chip. It also allows OTA updates using ESPHome. Otherwise, the functionality was basically the same as V0.  The only inconvenience with this version was the power. cable Water meters are usually installed in hard to reach areas of the house and don't always have an outlet near-by so I decided to look into making this battery powered.

There are a few problems with the current design to make it battery powered. Doing hysteresis in software uses a lot of power because of the continual sampling. The ESP32 modules have a ultra low power processor (ULP) which use ~200-300 uA when running. The LIS3MDL datasheet lists a current consumption of 40uA at 20Hz in low power mode. The power consumption goes up drastically from there once you increase the data rate. When you add it all up, I was getting close to 1mA which is too much for a battery powered device.

The LIS3MDL has a feature which sends interrupts above and below a threshold, but it doesn't let you set the positive and negative thresholds independently, which is required for hysteresis.

 I started designing V2 after the limitations of V1 were understood.