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contemporary IR light beam barrier

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Johannsen:
Hi,

I'm trying to figure out what the best concept is for a light barrier powered by AA-batteries

Most of the more modern circuits I found are using a TSSP4038 or a TSOP4838.

TSSP4038
https://www.hackster.io/mova2/long-range-beam-break-sensor-with-reflector-panel-4dfc48

TSOP4838  & CD4017
https://www.buildcircuit.com/diy-kit-19-remote-operated-musical-bell-diy-kit/

As I understand a continous ir beam needs more power but reacts fast. A beam with short busts needs less power but the reaction is delayed. Could be a problem when connected the barrier to a e.g. camera.

Avaliable designs are using NE555, CD4017. In this case the timer could be replaced by a low power 5010 http://www.ti.com/lit/ds/symlink/tpl5010.pdf

So far the ideas. Do you know better concepts or is this the way to go?

Kleinstein:
Those remote receiver chips like TSOP4838 are made for a relatively complicated modulation scheme: a double modulation with some 8-20 pulses (some 1-20% PWM) at a 38 kHz and than a pause of at least some 0.2 ms, better more.  So the obvious way to create the signal is using a small (e.g. 8 pin) µC, at least if one is familiar with µCs.  The analog way would be more like 2 timers like TLC555 or similar for the send part and some extra logic for the detection.

The modulation is at some 38 kHz (there are a few for some 50 kHz) and due to the modulation there is a delay of some 20-40 cycles. So one has to expect a delay of some 0.5-1 ms. It could be more for a  lower power version with longer pause. The delay is also not fixed, but more like sampling the barrier at some frequency up to about 2 kHz and than a little extra delay.

With just a simple 38 kHz modulation the system could still work, but less sensitive and thus more power needed. The speed could than be increased a little to maybe a 0.3 ms delay, without much sampling effect.

Modulated IR light really helps to reduce the power needed, as this helps a lot to suppress background light.

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