Salvaged IR sensor help

Can anyone help shed some light on what the pin outs might possibly be for these IR slot sensors I I salvaged from an old HP color laser printer?
Have tried a 330ohm resistor alternately on both outside pins, with the center used for GND. This based solely on assumptions gleened from various data sheets from different types of three pin IR sensors.

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My guess is that you have one common pin, one to the LED and one to the collector of a transistor.

Use a multimeter to find which is the LED then use your R to turn it on/off. The collector should have a 10k to 5v. Use your multimeter to see the collector voltage goes high and low.

Note the light will be IR so you will not see any light.


Connect a <= 5volt source with a ~1k resistor in series to the probes of a DMM.

Try all posible combinations on your sensor.

The one that reads ~1.2volt is the LED with the right polarity.

With a multimeter on the "diode test" range you do not need a series resistor. To see the IR LED light, use a digital camera to observe it as you apply the test voltage.

Right. The "diode measuring voltage" on my DMM is 3volts. That's should be ok to measure the forward voltage of IR diodes and standard ~1.8volt LEDs. It does not measure high efficient green/blue/white Leds, but they do light up. I don't know if all DMMs measure with ~3volts. Leo..

Wawa: I don't know if all DMMs measure with ~3volts.

This was a point of discussion a while back.

It surprised me to find that despite operating from a 9V battery, the meter limited the test voltage to about 3V - barely enough to light a blue or white LED. Presumably deliberate, so as not to cause reverse breakdown of sensitive devices.

It is most certainly current limited, so no other protective measures required while testing.

Guys, thanks for the tips! I'll definitely try those out and let you know what I find out. Once I get the pin outs nailed down I'll set up a simple test arduino sketch to make further verify that it works properly. Since the sensor is really just a slotted break-beam set up, maybe run the Vout to A0 and serial print the output.

Why use A0? The output is digital. You will need a pull-up resistor.