The low voltage PCB carries a Teensy LC, DS1621 thermometer, MCP3428 ADC and a few passives (I²C pullups, current limiting resistors for the SSRs, and a pullup for the zero cross detection optocoupler):

The DS1621 is used for cold junction compensation of the thermocouples and I already tested it. It's working fine! MCP3428 code and thermocouple temperature conversion will follow later (I hope today).