Infrared Sensor output voltage

Hello everybody!

This is something I have been fighting for a few days now. I have been collecting references online, but I am still defeated by an apparently simple problem.

I am hacking an Annew Robot Vacuum Cleaner. It is equipped with three IR sensors facing downward to prevent falls. Every sensor is impossible to extract from the casing, since it is not possible to unscrew them out. This makes impossible to read any vendor/model that may be written on the sensor.

The sensors feature 4 pins and from the outside they are presented as two small dark windows, so I assume they are made of an IR LED and an IR photodiode. This seems supported by the fact that I can make some current flow through 2 of the pins.

My tests are performed like this:

  • I power the IR LED.
  • I connect the sensor like in this diagram IR Photodiode Circuit Schematic – Fiz-ix
  • I read the voltage between ground and the point marked as ADC in the diagram.
  • I move a white sheet of paper in front of the sensor

As a result I get a very regular, reliable and deterministic change of voltage on my multimeter, good news.
The problem is that I get a very narrow interval, just a dozen of millivolt or two.

I also tried another wiring — comparable to the one shown in this picture https://www.arduino.cc/wiki/static/ffee7ca27509379fbac1be561d7435c8/4af8e/button_schem.png — and I get the same result: I can measure a deterministic change of voltage, but too weak of a change.

  • Is it normal like this and I should cope with this narrow voltage interval via an analog input?
  • Am I supposed to amplify the sensor in some way I am missing now and was not needed with IR sensors I used in the past?
  • Am I wiring the sensor in a bad way?

On the one hand I'd like to understand if I am stuck because of wrong expectations (a bigger signal), on the other
hand I'd like to fix this and move forward. All other sensors on board of the robot have been successfully reversed engineered and the robot is waiting to be programmed and roam my floor again! :smiley:

Thank you all for any feedback you'll be able to give me.

Seeing 4 wires is typical, two wires for the IR Emitter and two wires for the IR Detector. The emitter should be a pretty constant voltage. The detector should vary and it should vary more than a few mV. [Here is an example](https://www.semiee.com/file/ELMX/EXCELITAS TECH-VTR17D1H.pdf) of a typical IR emitter / detector. Many just have leads and no wires. Normally the Cathode and Emitter leads are at Ground. The Anode will go to a current limiting resistor and then VCC so across the actual emitter anode and cathode you should see the forward voltage drop of the IR Emitter LED. The detector Collector is an open collector output and should have a pullup resistor so the voltage should swing about 4 volts or more not a few mV. Knowing which pin is which is the tricky part.

Ron