I've hit a major snag in that my TEG is not generating enough constant power to adequately run the new thermopile amplifier circuit (typical draw in the datasheet is 100uA). Running the circuit off of the LVDO regulator dropped the LVDO supply voltage to roughly 1V where it should normally be 2.2V. The sensor still output different temperatures at different voltages, but I am not confident with the results as the op-amp rated minimum supply voltage is 1.8V.

More Design Changes

The project is heading off the rails again, so I will need to change things up. My plan is now to run the project off of a Li-ion battery, and rely on making up for the power used in the generation stage after the cup has been cooled down.

As the copper remains warm for a long time after being beside a cup, there is a lot of time here for trickle charging. I want to go with a battery as opposed to a capacitor so I can work with a more constant voltage level. Maybe if I get this working with a battery I will try a supercapacitor, but for now I don't want to complicate things so I can get the damn thing working.

I have a couple options I will be exploring for battery charging. 

1. LTC3108-1 + Li-ion charging module

The LTC3108-1 is the current energy harvesting chip I am using, I'll use the output of that to charge the battery. The charging module I've ordered is not specifically designed for low power trickle charging, so I am skeptical of how it will work. There are a couple LEDs on the module that show the status of charging, so at the very least I will be removing those to make sure there is no chance of wasting energy on those.

2. bq25504

A helpful user named Vinalon suggested this chip in this Hackaday article. This chip does both the low power energy harvesting as well as the battery management. I want to see how this compares to my current circuit.