Interfacing with Allen-Bradley Sensors

Two questions about interfacing with the Allen-Bradley IR sensors:

  1. How to hook it up: Are the outputs analog or digital (I’m guessing digital)? What are the output voltages of the green and white wires? If we assume that the output voltage is the same as the input voltage (12V) is it safe to hook it up to the robot controller?
  2. How to read the outputs: Now supposing that we have managed to hook it up, what are the outputs of the green and white wires? On the specs, one wire is labeled as “N.O.” and the other “N.C.”, which we think means “normally open” and “normally closed.” I would assume that one wire returns a 1 if the receiver has a signal, 0 if it doesn’t, and vice versa for the other wire, but am not certain. We can’t really test this ourselves without knowing the answers to question 1, “how to hook it up.”

If anyone knows the answers or learns how to interface with the IR sensors through something I may have overlooked, please let me know. Thanks!

Umm, did you read the spec sheet? That pretty much covers it.

To get you started:
There is a transmitter and a receiver. The transmitter just gets DC power (anything between 11 and 28 volts), red is +

The receiver also gets 11-28 volts, brown is + and blue is -.

The output is definitely digital - on or off. It may or may not necessarily have the correct voltage level to be interfaced to the “Digital” inputs of the RC - look up the specs for the RC digital inputs!!

The way the output works is this: One “output” wire is green (normally open) and the other is white (normally closed). That means that with no object in the way, the “switch” in the unit is either open, or closed. (If it is closed, current flows).

Depending on whether you have a PNP or NPN output (look in the spec sheet for the model number) you hook the ‘other’ output wire to either + or -, and the unit switch inside connects to the other power leg.

For example, if you have PNP, and want N.O., one side goes to + the other to Green, when something is in the beam, the green wire grounds and current will flow.

Does that help?


We use 3-wire, PNP prox switches. Our hookup looks like this.

Brown +12V
Blue 0V
Black (signal) to digital input (sig).

Now, to get the program to actually see the input we had to add ‘pull-down’ resistor.

We placed a 4.7K resistor between black (signal) and blue(0v). Works well.

Programming, we got satisfactory results sampling every 1 mSec. We use two prox switches to count gear teeth.


According to the parts list and the data sheets, the A-B sensor is NPN. I can understand how to wire a PNP sensor to the RC, but how do you wire an NPN sensor?

I attached a sketch of what should work. The NPN is a sinking device when it is made so I have added a pullup resistor. I have the signal going through an opto-isolator chip.

Opto-isolation is to keep the +12V for the prox isolated from the +5V.




Thanks Chuck.

Unfortunately I do not have the time to find parts to build custom circuits. I have no electronic support on the team. I will have to leave this for the off season and use one of the Banner sensors from past years.

This looks similar to the FP issue of last year, the vendor did not investigate what the requirements are for plug and play.

I would have expected an NPN output to be perfectly compatible with the RC digital input, with no additional circuitry required. The inputs will sense a contact closure just fine. They should sense an open-collector NPN transistor the same way. My advice: just connect it, signal to signal, ground to ground.

If I am right, the NPN prox will send a 12V signal, when not made to the digital input…I am not sure this will work. If I can dig up an NPN I will give it a try.

A sensor with an open-collector NPN output will send no voltage. It will provide a path to ground when active, and it will appear as an open circuit when not active. That is exactly what the digital inputs on the robot controller want to see.

If this isn’t how you thought it works, consider why you had to add a 12v pullup to your suggested circuit.

Our IR receiver only has a red, black, white, green, and fully-stripped (ground?) wire. There is NO blue wire.

Any ideas?