The control panel consists of a single, large carrier PCB, in which the STM32 motherboard, power distribution board, and each of the application-specific modules slot into. This carrier board is fixed to a large pelican case, which gets mounted onto the test stand.

The carrier board is relatively simple, it has rows of Samtec headers for connecting the motherboard and modules, and female Phoenix Contact headers for the power distribution board. It additionally takes the RS485 signals from an Ethernet port and converts them to TTL logic level signals.

The motherboard contains all of the firmware to read from sensors, i.e. PTs, TCs, and load cells, as well as to actuate valve solenoids, control the hot fire sequence, read/control igniter states via an ADC, and to send telemetry over RS485 to the operator panel.

Each module is relatively simple, and generally consists of some multiplexer, e.g. an I2C multiplexer for I2C controlled sensors, or a GPIO multiplexer, for SPI controlled sensors or for the solenoid modules. Modules all follow a template footprint, and have Samtec headers which enable plugging them into the carrier board and one another. The carrier board is designed in such a manner that any module can be plugged into any of the 6 slots on the board, without a change in functionality. Phoenix contact pluggable headers are also used here to connect sensors to the modules.

The power distribution board was designed after having issues with the power management system on an old iteration of the carrier board, which was designed in-place on the carrier board. Separating power distribution from the carrier board allows us to be able to quickly swap out our power solution with off the shelf modules when issues arise. The power distribution board provides 3.3V, 5V, 12V, and 24V outputs, and has a tube fuse for over-current and short-circuit protection.