How to cover the phototransistor so that it reacts only to IR radiation?

Question

Do it yourself

I am designing an obstacle sensor, I took an IR LED and an L-53P3C phototortansistor + an amplifying stage from a transistor. And in addition, it is possible to directly connect to the microcontroller port (the design is simple, without an ADC), but there was a problem, the phototransistor responds well to visible lighting. Is it possible to apply a material to a phototransistor so that it only reacts to IR radiation?

Answer 1

Maybe any plug from the remote control will do? There are those where the LED does not stick out, but is covered with tinted glass.

Answer 2

Somehow you approached the problem incorrectly, modulate the radiation - this will save you from flare and greatly reduce the energy consumption for "backlighting", from the side of the phototransistor between the controller port you put an RF filter and a rectifier on the same diode. A few additional elements and the problem is not terrible.

Answer 3

Logic levels from different light sources will be different - here it will not work without an ADC.
Lacquer coatings will absorb most of the radiation - a light filter is needed, in the case of a single photocell this is not advisable.

Answer 4

Photo shops sell filters that pass only IR. They are called IR pass filters.

Answer 5

You can also try mica. It poorly transmits the visible spectrum, but is transparent to IR radiation. It is used, for example, to make filters for IR fire alarms. But I'm not sure if its transparency will really be enough for this purpose.

Answer 6

Modulate radiation at the frequency of a specific TSOP. Well, in general, there are phototransistors and photodiodes that are sensitive mainly in the IR spectrum, another thing is that an incandescent lamp gives IR, and a lot more can be caught. TSOP will give a clear signal that can be used without an ADC.

Answer 7

There is GOST "Colored Optical Glass". There are guest brands of glasses with spectral characteristics. Under the IR (infrared glass) there are a few more rooms. So there are plenty to choose from.
In general, you can make glass to order for your spectral range. A 40x40 mm2 plate costs about 3-5k rubles.

Answer 8

for IR photocells, the light filter is already built in, your light source can simply emit in the IR range

Answer 9

It's not exactly the right idea to use a phototransistor. I would try to take an already assembled infrared receiver - there is such a one-piece radio component. The output is a digital signal. It's cheap. An example is TSOP1738.
The difference from a phototransistor is that it reacts not just to infrared radiation, but only to blinking at a certain frequency. That is, the variable component of the infrared light flux. Typically, the frequency to which such sensors respond is in the range of 30-50 kHz. That is, constant illumination will not cause operation. Only pulsating, and not even a constant background, it will be determined.
The fact is that just an optical filter will not give the expected effect. The world in which we live is full of not only visible, but also infrared radiation. So even if you filter out visible light, false positives will not stop. But there are quite a few sources of radiation pulses with a frequency of 40 kHz in the ordinary world. Of the common - only remote controls.
Try to think along those lines. You just need to feed the emitting LED not with direct current, but with pulses with a given frequency, and instead of a phototransistor, put a ready-made IR receiver.
It has already been suggested to "modulate" the signal. This is what it is. The only difference is that when using a "bare" phototransistor, you will have to solder or write filters that emit ripples yourself, and when using a photodetector, all this has already been done inside.