Which sensor should I use to detect that a polypropylene sheet (light
shines through) has moved past a certain point? Would be nice if
it could easily connect to an Arduino.
Electronic – arduino – Which optical sensor to detect polypropylene wipes pass by
arduinolight-sensorproximity-sensorsensor
Related Solutions
Use a permanent magnet and a reed switch.
Fix the magnet on the moving part and put the reed switch on the fixed part. Then monitor the reed switch with the microcontroller.
If your power supply is indeed the issue, then add a simple low pass filter in your power supply connections as close to the sensor as possible. I'd start with the following configuration to see if it improves the situation. Double check if Vcc at the sensor is 4V5 - 7V.
simulate this circuit – Schematic created using CircuitLab
Assuming that the device is powered by Arduino's 5V and assuming that the device is drawing 30mA of current, the voltage accros R1 will be 0.3V and the supply voltage for the sensor will be 4.7V, sufficient according to the datasheet. R1 and C1/C2 form a simple low pass filter that will suppress high frequency noise from the power supply.
Keep wires as short as possible, keep them as close together as possible. If possible twist the wires for the power supply and twist the wires (V(out) and GND) for the output.
Best Answer
A carefully calibrated noise-rejecting transmission setup probably could detect the attenuation of a typical wipe between the emitter and detector, but there's likely a better way.
Instead of transmission, use reflection. Put the light source and detector on the same side, and detect the illuminated wipe. Figure out a non-reflecting background to put behind it; something flat black and maybe a surface tilted at an angle such that any reflection would not return to the detector anyway.
If you cannot fully shield the setup from outside light, then you should make it reject interference. A simple method it so modulate the light source, and use a bandpass filter on the receiver (eg, how TV remote controls do it). But you can get a better analog result by using synchronous detection, where you alternately turn the light source on and off at a high rate and subtract the reading with the source off from the reading with it on. Depending on needed dynamic range you can do this either in circuitry or in software after A/D conversion.