Build a circuit to read a one-wire signal

Thread Starter


Joined Aug 4, 2018

I am trying to reverse engineering a wired air conditioning remote in order to automate it via openHAB...

Once opened the remote I faced myself with a three wires connection:
  • GND : Ground
  • 12V: Power
  • SIG: I assume “signal”
Please see pictures below:

after digging around I have discovered that the SIG wire is a signal that "instructs" the central air condition engine on what to do...

I have founded this article that describe a similar case, but my level of knowledge is minimal:

I am at step one: how do I build a digital circuit to reverse engineer the signal from SIG wire? anyone else have better ideas?

Thank you all


Joined Mar 10, 2018
If you do not have a scope -

You can start with a PC sound card based scope for free. Will give you basically
audio range scope, spectrum analyzer, and function generator all using your
PC sound card.

But first build a simple circuit to protect sound card inputs so you do not
ruin from transients, overvoltage. Google "protect sound card input".

For example

Sound card impedance bridge -

There is low cost logic analyzer, good to several Mhz, ~ $10

Search ebay for USB oscilloscope, quite a few offerings that will get you >> 1 Mhz.

And function generation and others -

Regards, Dana.

Thread Starter


Joined Aug 4, 2018
Search ebay for USB oscilloscope, quite a few offerings that will get you >> 1 Mhz.
I have looked at the this on eBay and AliExpress:

anyone can suggest something cheap that would do the job?

Also a $ 5 Arduino, would also work for my purpose? and will it work for may other projects or has more limitations?


Joined Feb 20, 2016
An oscilloscope is a must have tool for electronics. They are often called "truth meters" as they can reveal so much of what is going on.
If you can afford one that has serial data decoding built in, that would make it a lot easier. A digital scope that stores a one time signal for display is the norm now. My old CROs did not have that facility so it was a lot harder to see non repetitive signals.

Another tool that can be useful is a Bus Pirate..

As Dana mentions above, Ebay can be your friend.