The project was born from the desire to automate the home's electrical system.

Arduino is a good platform that allows rapid development of the prototype, but for complex projects it still has few inputs, so I needed something to allow me to detect the state of the loads (light, generic loads, electrical outlets) using a few pins.

With this board it is possible to use 4 pins to select the multiplexer input to be read, one pin to enable the multiplexer common pin and finally another one to read the status of the selected input. By stacking two boards , it is possible to read a further 16 inputs using only two other pins (one only if in addition to the selection pins the sharing pin of the multiplexer is also shared) and so on.

The detected status present on the COM output has a level ranging from 0 to 5V suitable for being connected directly to a digital port of the microcontroller, on the board pullup's resistors necessary to maintain a stable logic level are already present even in the absence of the connection or active load. The output is normally at the high level (5V) if there is no current flow in the selected input, low (0V) if there is current flow at the selected input. All inputs are opto isolated to ensure the necessary isolation between the logic and power parts

The board is configure to read 24V AC, to use it with 12 V AC the resistors from R9 to R24 must be replaced with 1K 1W resistors.

To use it with 48V AC the resistors from R9 to R24 must be replaced with 4.7K 2W resistors.