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Recommendations for GPIO expansion?

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Eric Flament

I'm surprised this question doesn't appear in the forums or blogs.  I figured I'd ask here rather than thru a support email....

I have a project that requires 100+ GPIO connections.  Do you have any recommended hardware for GPIO expansion?  I'd prefer not to add a second Arduino/RasPi PLC.  It would also be nice to just have a I2C GPIO expander rather than having to interface Modbus and learn some kind of proprietary protocol.

I'm considering just buying multiple PLC controllers and learning NodeRed as a transparent way to access their GPIO with minimal firmware, but I'd really prefer zero firmware and microcontroller involved in the extra GPIO.  Does Industrial Shield sell additional standalone I2C modules like the ones in the RasPi PLCs?  Or do you have a preferred vendor for GPIO PLCs?

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Eric Flament
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Actually, seeing your blog post about Arduino PLC + NodeRed, I like that solution.  I had not heard of "firmata", which seems to make the Arduino transparent in a way that I was hoping for.  I think I'll use a few Arduino PLCs and then control them via a Pi PLC hosting NodeRed.  I was worried about writing and deploying custom firmware to the PLC, but this standard firmata sketch seems to take care of it.

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Dear Eric,

No, sorry but we do not have any IO's expansion module. The solution here is to use multiple PLCs, as you have commented. You can acquire as much PLC's as your IO's combination require and then connect them with your preferred communication method (ModbusRTU through RS-485, ModbusTCP through Ethernet, I2C, etc.). Then you can use one PLC as the Master where you are going to manage all the other PLCs, which will act as Slaves (like expansion modules). Node-RED, as you have commented, can also be an option.  Which kind of GPIOs do you require (digital/analog/relay)? If you want, you can send us the details to [email protected]

Thank you,

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Eric Flament
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Thanks you for the response! I need digital GPIO. A second PLC module, like the 57AAR, would do the trick but then I'd have to synchronize the controllers (which is why I was looking at NodeRed). I would just hope to be able to add two 57AARs together to get a 114AAR but only worry about one Pi/Arduino controller. I thought about trying to access the I2C expanders in a second Pi PLC directly, bypassing the controller, but its clunky and I suspect that it won't work since I cannot change the addresses to be different from the Pi PLC I'd be trying to use to talk to them.

I'm sure there are I2C digital modules online, but I'd really like to be able to configure the output voltages like you do with the QVdc pins. Its not easy to source an I2C PLC with a wide voltage range like the ones you use. I was hoping you'd have a recommended brand/part. If you don't have anything, I'll just post whatever I find here, if I do find something. Thought it would be worth asking first.