I’ve quickly cobbled together a rechargeable lithium battery circuit and stuck it into a box with an Arduino, a temperature / humidity sensor and a temperature / pressure sensor.

It hasn’t exploded yet.

This was the circuit I used to test it was working (using the battery charger and step up DC-DC converter to power my flammable gas sensing circuit, because it was within reach).

This evening I re-wrote an Arduino program of mine that takes measurements from a DHT22 temperature / humidity sensor and BMP180 temperature / pressure to make it work with and Arduino Nano with an LCD screen attached. I’ve not used a Nano in ages, but sadly, I needed the 3.3v regulator to drive the BMP180. Hopefully it won’t be drawing much current and so not wasting much energy, after I went to the effort of using a reasonably efficient step up converter. I did check, and the voltage straight from the battery is also too high. Future plans include… not using 3.3v sensors.

Here is a video of the box running off the battery.

I’ll tidy up the circuit – perhaps move it from breadboard and a pile of bits onto protoboard, make the charging port accessible, add a power button, menu buttons, battery voltage monitoring, auto power down for low battery / after inactivity and perhaps add an external 1 wire bus for DS18b20 sensors. At that point I’ll document what I’ve done a little better.