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Generic Input Module?


Hello - I’m very encouraged by the selection of hardware modules and the support… however I do have one requirement that I can’t find a solution for.

I need to run 120V line voltage about 500’ away to a button that, when pushed, is detected by some sort of generic input module. I see the GPIO pins but I was hoping for a solution in board-form that wouldn’t require much external soldering and hacking.

The closest thing I can relate to is PLC (programmable logic controller) hardware which have input and output modules. The output modules are akin to the 10A relay modules that are available (yay) but I don’t see a solution for recognizing input except for low voltage buttons and stuff like that.

Does anyone know of a “clean” off-the-shelf solution for this? Thanks in advance!


Welcome to the forum!

Can you please tell a little bit more about your project?


Sure… I’m building a small automation prototype that consists of hardware inputs (which I need to figure out) and relay outputs. In a nutshell, when a combination of inputs are triggered, an output relay sequence will begin.

The easiest way to explain this would be to imagine a Christmas light show choreographed to music with a “start show” button mounted 500’ away. I currently accomplish this with off-the-shelf PLC hardware which allows me to send anywhere from 12VDC to 250VAC to an input module and that registers as the input being “on”.

So I’m trying to replicate a simple setup like this on the .NetMF platform but I can’t find an input module that will work - perhaps the GPIO pins and I step-down the 120VAC to 5VDC?

I’m more of a software guy, not much of a hardware guy, so off-the-shelf or simple circuitry is what I’m looking for.


Hi and welcome.

I don’t really understand the 500’ 120VAC requirement, can you elaborate? Why do you need 120VAC, is there any reason why it needs to be that? What about changing the way you send the “signal” to something like wireless, like zigbee ?


Hi Brett - thanks.

I have to interface with existing photoelectric sensors that run on 120V because of the long distances. Unfortunately wireless and D.C. isn’t an option because of the environment. This is the kind of hardware we typically use (copy/paste, the url is broken):

After thinking about this more, I guess what I need is a simple 120V to low volt D.C. conversion circuit. It could be as simple as a wall wart although I’d much prefer a module that could simply plug into the board and looks much more clean and professional. Plus I’d like something opto-isolated for safety.


I would recommend using a digital input…

Digital requires a high voltage of 3.3-5V for a one and close to ground for zero. You could connect one end of the wire to the Spiders ground and the other end to a digital input on the Spider with a pull-up resistor. You could then use the switch at the remote side to ground the input. Due to the length of the 500 foot wire you might have some issues with resistance. Sound like an experiment is called for :slight_smile:

The digital solution does not require an voltage to be sourced at the remote, just a button.

Of course, you have read the Beginners E-Book, which discusses all the available inputs? ;D


I definitely want to leverage the digital inputs, my challenge is finding a nice opto-isolated pcb or module that drops 120VAC to 3-5VDC so I can drive the input.


How about a wall wart?



Actually something like this is probably what I need:

It senses 120V input and returns TTL which could drive the GPIO pins.