i finished my next project : Digital Input / output shield with following features:
- 7 digital outputs
- 13 digital inputs
- I2C terminal connection (displayes, sensors...) And if will be available to program ND as I2C slave device you can extend number of IOs. Currently i am using arduino for I2C slave devices
And Voltage for IO is 5-24V DC. So it is my small "PLC".