I have a working set-up to detect beam breaks using an IR LED, modulated at 36kHz, and a TSOP receiver connected to a comparator. It outputs the count via Arduino. The range is about the width of a door, say two meters maximum.
The transmitter and receiver are on a separate breadboards. This has its disadvantages, such as two sets of batteries.
Is there a way to reflect the IR LED off a reflector and having the TSOP receiver on the same breadboard as the LED? Perhaps behind it? The German term 'lichtschranke' seems to be what I vaguely have in mind, but I don't speak German and can't find it in English.
Does anyone have suggestions on how to modify my current set-up or can anyone point me to some schematics?
I am guessing something will need to be done in order to maintain a straight or angled beam and not have it reflected back all over the place.
How can I mount an IR emitter and receiver on the same circuit board to detect a reflection instead of a straight beam?
Best Answer
You need a retroreflector, which is a special type of reflector that sends light back towards its source (unlike a simple mirror).
This is what you'd put on the rear of your bicycle to reflect the headlights of incoming drivers back at them so they see you at night. You can get them for cheap in any bicycle store or supermarket. Even better, shown below is one that is designed to be screwed at the back of a trailer. If you want to mount it with a screw, that would be a nice choice, as it already has a hole.
Next, put your IR LED and TSOP receiver close to each other, both aiming at the reflector, and perhaps a black plastic or cardboard separation between the LED and TSOP... Adjust LED power down to make sure the signal is detected with the reflector, but not with IR light bouncing off the people you want to detect, and you're all set.