I’ve gotten all of the sensors working at once now. One of the changes is that I’m now using a ’24’ bit differential external ADC. I’m using the NAU7802, which communicates with I2C and runs at a very slow 10-320 SPS. This is plenty fast and seems to be high enough resolution to measure GSR without any external amplifier. The ADC also has an internal PGA which hasn’t been nessesary so far.
The spikes in graphs below for red and IR correspond to heart rate.
I made several attempts dead-bug soldering the NAU7802. What worked best was to glue to face down on a peice of cardstock and then just solder to the prongs from there.