I have been developing an accessory board for the Pi that I call Octa-Pi(provisionally). It provides the Pi with 8 high level (24VDC,1/2 A) outputs and 8 digital inputs, similar to a PLC. At the bottom is a link to a (crude) video of my prototype. It uses 4 of the GPIO to generate the 16 I/O and will be expandable in blocks of 8+8, without using more GPIO. All I/O will have status LEDS (Yellow out, Red in in the video). Other useful features are an integral power supply that can use any DC source , 8-24 Volts and it will output 5 V, 1A for the Pi via a USB connector. In the video it is running from an old laptop charger. All outputs are protected against short circuits and inductive loads. THe Pi GPIO connect to a dedicated protective buffer. In my test each IP is connected to the corresponding OP and a Python test program runs the pattern, checking that inputs are correct. The result is printed to screen. A single function called with a list that is the needed output status returns a list of current input status. The connectors used will be standard industrial crimp on 1/4" slides; easily availabe and easy to use. It will have a proper wire to board header for the GPIO pins, not a ribbon type insulation displacement. I plan to market it as a complete kit, including connectors and a printed labelling kit. It would be a phenomenol education tool as many hardware principles are also demonstrated.
I have been designing and building industrial control systems for 30+ years and have tried to integrate my acquired experience.
One thing I have noticed with the Pi is how critical power loads are (keyboard et al) for a production version I may build in a self powered USB hub, if feedback is positive.
The 'Octa-Pi' would also function with any other similar micro controller with low level bi directional I/O, even perhaps the LPT port on an older computer.
I welcome feedback. Currently I am designing the PCB layout and hope to have 'proper' prototypes ready in about 3 weeks.
A Jackson
Oakwood, Ontario
Canada
