Mdthbs

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?

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.

Yes, you can put the IR LED and IR detector next to each other with a reflector on the other side.

A corner reflector has the advantage that it doesn't need to be aligned perfectly, it will reflect the light back where it came from. The retroreflector that peufeu referenced is composed of many tiny corner reflectors. These should work with near infrared, but it would be safest to find one that specifically says it is good for near IR.

You can also use polished aluminum as the reflector. For a recent project I used 3" x 3" x 1/16" aluminum. I sanded it smooth with ultra-fine sandpaper. Then, I polished it with car polishing compound until I could see my reflection clearly.

To minimize stray light on the detector, you can put a small tube over the sensor.

You can mount your transmitter and receiver next to each other, but you'll need to block the direct light path. Here are two examples of pre-build products. I would model a design after the first example; I'm not sure the isolation of the second example is sufficient.

And, yes, you can use a reflector, but make sure it is appropriate to your IR wavelength. For example, a standard bathroom mirror won't work well. These mirrors are often aluminum under glass. The aluminum reflects well, but the glass absorbs IR.

Some plastics absorb IR, whereas others reflect it. You may need to test different options.

The best IR reflectors are often metal (copper, aluminum, silver, etc). Here is a chart showing the reflectivity of different metals at different wavelengths. It looks like copper, silver, or gold will outperform aluminum at typical near-IR frequencies.

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Look for line or proximity IR sensors. Some even detect distance. Many are compatible with bread boards or can be wired to them with 0.1" jumper wire or headers. They have the detector and sensor built into the same module as the one shown below.

Source: https://www.digikey.com/product-detail/en/sparkfun-electronics/ROB-09453/1568-1272-ND/5762422?WT.srch=1&gclid=EAIaIQobChMImKyvqPLI4wIVhcpkCh2mpwiNEAQYBSABEgJe5fD_BwE

Yes, it is very possible. You just need to arrange the LED and detector appropriately.

IR is just light that your eyes can't see. If you were trying to do this with a visible LED, what could you do?

For example: You could put the LED inside an opaque box with a hole at one end, you could make it more of a "pinpoint" type of light. You could put the LED and detector next to each other with a wall between them.

Putting a reflector on the other side is the obvious and trivial answer. But it won't work completely reliably as a beam break detector because of reflections from the very objects which are breaking the beam. For exactly this reason a distance measuring is SPAD LiDar module is a better bet. Since your objective is a doorway of less than 2 mtrs, this is perfect. Simply do fast, continous distance measurements. If the result shows less than (say) 4ft, then count it as a beam break. There some excellent cheap modules available now... $5-10 range. I'll post the part number as soon as I remember it.

Ok... VL53L0X is one such.