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I Need a Device that Can Tell a PC the State of Relay Contacts

pete.cal

Nov 19, 2022
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A friend of mine needs to know when his furnace turns off and on. He has installed a relay that switches state when the furnace changes.
All he needs is a USB device with two wires hanging out to place across the relay contacts (and maybe a pull-up resistor). Maybe some software to log the changes. I thought finding something like this would be easy but I can't seem to turn up anything reasonable.
I found a $260 device with no software support.
A sparkfun device for $19.99 but again no software support and requiring both Arduino coding and PC coding.

If needed I could whip up some VBA code for the PC but I don't have the time to learn Arduino. In the distant past I did a lot of assembly language for the same chip family as the Arduino but I'm not ready to restart that stuff.
Any ideas?
 

kellys_eye

Jun 25, 2010
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This device was originally designed to allow old analog joysticks to connect via USB but will accept multiple digital (switch) contacts as inputs as well as varying voltages should you need them.

AFAIK this is one of the cheapest ready-made such modules out there. Someone may prove me wrong though!

 

Bluejets

Oct 5, 2014
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You already have a "device that can tell the on off state" and that would be a set of voltage free contacts on the relay.

Instead, I'm guessing you need to interface somehow to a pc.

Rather large open ended requirement due to just what program, software, whatever you are running on the pc that can see and use that information.

If needed I could whip up some VBA code for the PC but I don't have the time to learn Arduino

Glad you think it's soooo easy when in all you have to ask here "how to do".... :rolleyes::rolleyes::rolleyes:
 

pete.cal

Nov 19, 2022
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You already have a "device that can tell the on off state" and that would be a set of voltage free contacts on the relay.

Instead, I'm guessing you need to interface somehow to a pc.

Rather large open ended requirement due to just what program, software, whatever you are running on the pc that can see and use that information.



Glad you think it's soooo easy when in all you have to ask here "how to do".... :rolleyes::rolleyes::rolleyes:
Right, as I said, "All he needs is a USB device with two wires hanging out to place across the relay contacts (and maybe a pull-up resistor). ".
Also, "If needed I could whip up some VBA code for the PC but I don't have the time to learn Arduino"
It would be easy once I got the state of the relay into the PC. I did it many times back when PCs had printer/parallel ports.
 

danadak

Feb 19, 2021
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Take a look at Tuniot on a ESP8266 pr ESP32. Simple to build client server applications.



Regards, Dana.
 
Last edited:

Harald Kapp

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Nov 17, 2011
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Use a 1-button "keyboard" like e.g. this one:
1704950590632.png
Replace the key by the relay contacts (or simply connect the relay contacts in parallel to the key as there sure is a small pcb inside the case). Setup software needs to be downloaded but no programming of your own is required.
Then assign the "key" any suitable value (or even combination of keypresses). Use any software you like to react on the "keypress".
 

pete.cal

Nov 19, 2022
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This looks like the best solution I have seen.
I will see if he wants to go with this.
Thanks.
 

Tha fios agaibh

Aug 11, 2014
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Right, as I said, "All he needs is a USB device with two wires hanging out to place across the relay contacts (and maybe a pull-up resistor). ".
Also, "If needed I could whip up some VBA code for the PC but I don't have the time to learn Arduino"
It would be easy once I got the state of the relay into the PC. I did it many times back when PCs had printer/parallel ports.
They do sell usb to serial and usb to parallel port adapters inexpensively.

If a one button keyboard is pricy, you could also tear an old keyboard apart and convert it.
 

pete.cal

Nov 19, 2022
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I actually have one of those I bought a while back "just in case". But I need something more turnkey. This isn't my project. I was just looking for a device for a friend. Not another project.....I have enough of those to do already.
 

mineymoe

Nov 14, 2023
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It sounds like the single-button keyboard idea is probably the easiest turnkey solution here. No programming is required on your end. I'd pass that suggestion along to your friend. It should be pretty plug and play for monitoring the furnace relay contacts.
 
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