I recently had a need for a simple digital controller something similar to a simple PLC (Programmable Logic Controller). I wanted to use the Arduino board I had but I couldn’t find any I/O shields that had the right mix of relay outputs (6) and opto-isolated inputs (6).
I know I could stack shields but the enclosure I had wouldn’t allow it. So I’ve put together a oversized (its a lot wider than your normal shield) Arduino PLC shield schematic which has 8x Relay channels and 6x Opto-Isolated channels and some analog inputs as well. The final number of relays and opto’s channels may change but I’ll post it and a PCB once it’s finished.
An update can be found here:
Arduino PLC v0.20