This is the bottom board that I designed to fit into the BUD DMB-4774 DIN rail mounted PLC case. It carries the MEGA2560 Pro Mini board (on the left) and the ESP32 board (on the right.) All of the controller code runs on the MEGA2560 (more than 4,000 lines of BascomAVR which I’m converting to Great Cow BASIC right now because the guy who wrote BascomAVR is a dick and GCB is far more feature rich) and the ESP32 does all the WiFi over the MQTT protocol (more than 800 lines of Sketch.) There’s also a dual FRAM card standing on edge below the ESP32 which I use to store logs.

The green connectors are 9-place pluggable 5.08 mm screw terminals that let me unplug a whole block instead of undoing a bunch of screws (VERY handy.) The 20-pin box header on the left edge connects to the top board which does the HMI stuff.

The labels on the connectors are things like:

BFS - Bottom Float Switch (in the releaser) TFS - Top Float Switch VS - Vacuum Solenoid AS - Air Solenoid LVL - Releaser Level (an IR laser TOF sensor) PVT - Pump Side Vacuum Transducer CVT - Collection Side Vacuum Transducer VP - Vacuum Pump

That’s the first block. The other blocks have similar meanings.