The main goal for V2 was making it battery powered which turned out to be extremely difficult. First, the PCB and case was expanded to make room for three AA batteries.

Then I started replacing/adding a few components:

• RT9080-33GJ5 regulator due to its low quiescent current.
• PCF8563 RTC as a low power clock source for the circuit and time keeping while the ESP is sleeping.
• ESP32-S3 replaced the discontinued S2 module
• RGB LED + lens for user feedback
• MB85RC64TA FRAM for storage
• ALT021-10E magnetometer

The major hurdle was finding a replacement for the LIS3MDL magnetic sensor. Having already exhausted my off the shelf sensor solutions I had to make something from scratch.

I started by designing a circuit using the DRV5055 hall effect sensor with an opamp and comparator to implement hysteresis. TI has a great document with some example schematics.

The current consumption isn't too bad at 10s of uA, but it's starting to add up.

Here is an example of why you need hysteresis when counting zero crossings in an analog analog. The noise in the blue line causes the threshold to get triggered multiple times (red)

The DRV5055 consumes 10s of mA which is far too much so it's power needed to be duty cycled periodically. This would require a low power oscillator and transistor. At this point the bill of materials and circuit complexity was getting larger than I liked so I looked for another solution.

I settled on the SLG46826 by Renesas. It is a programmable mixed signal matrix. Similar to an FPGA, except much simpler in capabilities. It's designed to replace digital glue logic to save power and board space. In this case, I was able to replace the comparator, duty cycle and interrupt generation circuit with it.

That's where the state of the project is today. I realized this platform can be used as a generic data logging device for all types of sensors (e.g. power, gas, etc) so that's what I'll work on for V3. The major requirement missing for this is making the case waterproof.