I’ve managed to find some time this week to put together a draft schematic for the PLC shield.
I’ve only included 4x opto isolated inputs as I happened to have some TLP521 Quad Opto’s handy. I’ve added a couple of extra analog inputs as I may used a Seeedstudio v2.12 Arduino clone and that has an extra two analog pins so it makes sense to have them available and I’m still need to find a spare control signal to control the RX/TX enables for the RS485.
An update can be found here:
Arduino PLC v0.20