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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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