High power I/O shield for PLC

I am going to develop an I/O shield to interface with 24V pneumatic valves and proximity sensors.
Basically the shield will have the following characteristics:

  • 16 or 32 24V relay output to drive solenoids (around 100mA)
  • 16 inputs : Driven at 24V for proximity sensors
  • Serial/USB conversion using an AVR32 UC3 uC: used to program the arduino/act as an arduino
  • bidirectional RS485/RS422 port to remotely control other PLCs
  • Option to control it directly from an Android device through either Wifi or Bluetooth
  • Basic user interface with knobs and LEDS. (Don't know if a LCD interface is needed)

Power supply will need to be able to support 5 amps current. We will avoid SMPS as they don't like high current at startup time.

Basically, it will be used to replace a COMFILE module and it will be used to drive a robot connected to a molding machine.
The robot is already in use, controlled by the COMFILE module, but we want to replace it by an arduino.

I would like to have your feedback about the specs and to know how many people could be interested.

Not sure if this project is still alive.
The scope of what you are trying to do appears to be beyond one shield.

there has been a lot of discussion about using an Arduino as a replacement for a PLC and in many cases it would be a great fit.
however, an industrial PLC will be darn near bulletproof and have multiple layers of protection.
also, an industrial PLC will be much faster than an Arduino.

That said, probably half the installed PLCs could easily be replaced with an Arduino.
but, it appears that what you are looking for is a module to be added to an existing PLC system ?

It appears that you also want the unit to be available to others ?
obviously, the closer you get to the core micro, the faster things operate.
you could make a shield that works of an I2C bus or SPI and use a multiplexer to turn the relays on and off. this offers a layer of protection in the event of a failure, but adds two levels of distance from the micro. The bus and the multiplexer.

I personally prefer to use either ice cube relays or SSRs. this keeps the high power out of the control box and allows relays with different ratings to be used. if you want to have 24VAC as the control signals, both in and out, you can develop an interface for that. I too prefer 24VAC as it is so common in use.