The hardware is based around two custom designed PCBs, one for the power supply / IO module, and the other for the display module.
IO Module - 2 layer
The power input comes from a three position 7.5mm pitch screw terminal block, with the live splitting to each relay, and the primary power supply. The primary power supply is a 24V, 1A medical grade open frame wide input range switched mode power supply. It is designed for direct PCB mounting and is protected by a 1A slow-blow ceramic cased fuse and a MOV. Each relay switches mains voltage, and the contacts are protected by a snubber network, for switching inductive loads.
The 24V output is fed out to the display module, the inputs, output relay coils, and to the secondary power supply, a 24V to 5V buck regulator. This provides all the remaining power for the board.
An STM32F103RBT microcontroller provides overall control, and drives the output relays via MOSFETs, and reads the inputs via PC817 optoisolators.
An RS485 interface is provided, with termination, for communication with the display module.
Finally, a bi-colour red-green LED is provided for a status indication.
Display Module - 4 layer
The display module takes a 24V supply from the IO module, and an RS-485 data connection. The board is controlled by an STM32F103RET microcontroller, the extra flash space needed for font, image and language files.
In addition to the high resolution (240x128) 32 greyscale display, the display module has an interface for a 4x4 matrix membrane keypad, a supercapacitor to provide backup for the RTC within the microcontroller, a USB interface, based on an FTDI FT232RL single chip solution, LM73 temperature sensor, TEMT6000 ambient light sensor, piezo buzzer and 256kbit of FRAM for high endurance non-volatile data storage.