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Topic: Reverse engineering 5V sensor (Read 468 times) previous topic - next topic


I have various sensors that all output 0-5V analog.
these are sensors like temperature, pressure, etc for students

They use a RJ45 cable (like ethernet) but I don't know the pinout of the cable and cannot find that info online, also I cant look at the PCB since its inside a plastic box which I cant open.

I would like to reverse engineer which pin is what. There should be +5V  GND and Signal...

but how to do this without frying them? I mean would they fry if I just go brute-force and try all combinations? Like if in one of my attempts I supply 5V to the signal pin... or to the GND...etc?

thank you


If you tell us the make/model of devices your talking about or post pictures then maybe someone here will recognize them and have the info you need.
I might seem like an idiot but remember it takes one to know one.
Forum user generally fall into three categories (the good, the bad & the a**hole) what category do you fit in?


I agree. It's probably best to post pictures and see if someone know it. I will not bet on it but I think you got a fairly good chance to fry out some sensor by going brute force since you don't know what is in the box...  :~

Maybe trying a "Bus Pirate" ? I don't really know...


Yes, you can fry them.
For reverse engineering, you could make an X-ray of the plastic box  XD

Are you sure they are only the sensors ? or do they have an ethernet chip inside ?

Sensor boxes with RJ45:


I got the DAQ (USB which connect to a computer) for these sensors (these are those school sensors like Vernier style) Vernier publishes their pinout, but these are cheap copies so the pinout is unknown, but now that I got their

What if I breakout the ethernet into a breadboard, so as the sensor is talking to the DAQ, I can use an oscilloscope to sequentially test all wires until I find the +5V GND and signal wires?
I just got the oscilloscope so I'm not sure... if I bridge two wrong cables, will it fry... or the oscilloscope protects it?

Thank you!


Most oscilloscopes has the ground pin grounded to the mains earth/ground. It is better if you know what the ground signal is, to prevent the ground of the oscilloscope accidently connect to the 5V of the sensor.

If you can power the sensors and test the signals, you can use a multimeter.

Are the modules not like the ones in the link I gave ? I think those modules use RS-485. What about a photo ?


Looking for ground was good advice.

What i did was, connect sensor to its original usb DAQ, then with multimeter in continuity mode i tested betwern each of the sensor pins and the USB plug GND pin, since this is known.

I did this with the DAQ unplugged from the computer and i tested betwern the USB plug that would go in  the computer, and the socket where a sensor would plug in.

Once i found what pin in the sensor port is ground, i connected the DAQ to the computer USB and in Voltage mode i tested on the sensor port between the GND pin i had just found, and every other pin.

This way i was hoping to find a 5V signal.

What i found was

Pin    Volt
1    0v
2  2.3v
3   2.3v
4   2.3v
5    GND
6   5v
7   5v
8   7.8v

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