Using a 4 channel logic-level MOSFET with many amps capacity per channel, I wanted to overhaul a peltier fridge with a dead powersupply. I've got the internal fan and heatsink fan plugged into two channels, and each of the peltier coolers, 4A each, plugged into the other two channels for load balancing (putting a heatsink on those mosfets will be a pain because the tabs are the output switched ground).
I've taken the 10k thermister from the inside of the fridge and plugged it into one of the ADC GPIOs. I've added 2 other DS18x20 1-wire temperature sensors, one reading the heatsink's temperature, and the other reading "ambient" (or at least, inside the case of the back of the fridge, maybe reading a couple of degrees above ambient if the peltier is pelting.
Finally, I'm running all this from a XBOX one power supply, that outputs 5v standby, and switched 12v. The switch handily takes 3.3v signal voltage, so I enable the power supply when there's been demand on any of the PWM channels for at least 10 seconds, and switch it back off when there's been no demand for 10 seconds.
And I'm running all this from an ESP32 devkit running Tasmota, with PID controller compiled in. My user_config_override.h is included in this repo.
After the kit was given a basic config with GPIOs per wiring.txt, I ran ansible over it using my Ansible config to configure all the parameters and their names (for Home Assistant's benefit).
Upload autoexec.be to the Tasmota filesystem to be interpreted by Berry script at bootup, and you have a peltier fridge! On the device webpage http://fridge1 if you go by the rest of my ansible setup), the first slider is your setpoint temperature (unlabelled). When twiddled, the setpoint value is reflected in the "Set Point" field. The next 3 sliders are the instantaneous demand values at time of page-load, for the peltier cooler and internal fan (slightly offset from the coolers themselves), and the final slider is the demand for the external heatsink, which is more a function of the difference in temperature between heatsink and ambient (ie, how hard we should be driving the fan to extract excess heat from it).
PID loop tuning is done by writing to PWM6, PWM7 and PWM8 per wiring.txt. Default tuning of the PID loop is to have a time constant of half an hour, and a proportional band of 1.5degrees. If your fridge can't keep up, you probably want to slow that down a bit (but that will take code change, because that represents the maximum values I allowed for those PWM. Adjust Pb, Ti and Td by writing 0-1023 to each of PWM6 (Pb, scaled to 0-5degrees), PWM7 (Ti, scaled to 0-1800 seconds) and PWM8 (Td, scaled to 0-450 seconds).