Upgrade PCB - radensb/T-962-improvements GitHub Wiki

There are several versions available, but I wanted to make my own. My design incorperates four of the MAX31850K devices to provide cold junction compensation and four thermocouples (completely replacing the original analog interface). The 1-wire approach made the most sense to me as no additional components were needed. There is an onboard FTDI MAX232 interface and external USB connector to allow for programming and UART interfacing. Finally, a transistor to control the system fan. The PCB is mounted to a custom bracket that used the original PCB mounting holes and places the new board near the top of the lid where it is away from the insulation, foil, and heat.

The first two thermocouple interfaces are for the ones that hang in the heat chamber and measure ambient air temperature. The other two intermocouple interfaces are designed to be connected to the PCB being reflowed to measure surface temperature. I 3D printed a box that has two K-type thermocouple sockets which allows one or both thermocouples to be removed if desired. If any of the external thermocouples are not present, they are ignored by the firmware.

There are thermocouple wires connected to the PCB that run through the air vent into the box and attach to the sockets.