I have been using Arduino and various Atmel AVR uC for many years. Though the software part has very wide user group and is well supported, hardware design gets frustrating sometimes.To overcome some frustration, I have made a flexible Arduino compatible I/O board with 8 I/O. Yes you can configure any combination among the eight I/O unlike the fixed ones found in PLC. To convert an output to input you have to remove the Optocoupler (4 pin) and flip the pins backwards and re-insert it. If no one has done it before I will call it flipOpto
design.Further the I/O has different single connection for Input and output. Nothing else is needed on low voltage side. The Output is open collector and same way Input has to be open collector.
The Arduino area is preserved to receive most of the shield. An example with Zigbee shield
The Board is without any issue other than I have decided to go for N channel mosfet intead of Bipolar Transistor, hence have to flip it on the screen print.
It also features area for a analog voltage divider so that you can get 2x high voltage in. It has big resistor space for through hole resistors.
Any Arduino I/O can be connected to any Board I/O, hence you have all the freedom.
Though I have designed it for my use (in end product) but I have couple of PCB ready with me and I will go for more if accepted. I can offer the PCB or completed board (without testing).
Please also let me have your view on this.