Power Module 3

Back side:

An "Arduino Nano 33 BLE Sense" shield that...

Supplies 5V (V+ pins) from a TSP61220 step-up converter,
- This voltage also powers the Arduino
Supplies 2.5V (Vref pins) from a voltage divider + LM321 opamp,
Is powered by a 1.2V AAA battery on "Keystone 82" battery clips,
Exposes 3 digital and 8 analog pass-through pins for the Arduino
Provides jumpers for
- Enabling the reference voltage circuit
- Connecting Arduino's A7 to the + terminal of the battery to measure the battery level
- Two software-configurable pins that you can ground with a jumper
Dimensions: 47.63 x 31.34mm

Placed the arduino and battery side-by-side instead of on top of each other. This makes the board wider and less tall, making it fit better on the forearm.
Added more capacitors all over the place
Added various jumpers:
- A solder jumper to enable/disable the reference voltage generator, in case I come up with a setup where I won't actually need it
- A solder jumper to sacrifice one electrode and use its analog input pin to measure the battery charge instead.
- Three configuration pins, connectable via jumpers, to change software settings on the fly and toggle between up to 4 different modes. Or you can use them to plug in an extra module.
Hopefully fixed the layout for the step-up converter