Help understanding an IR Receiver circuit.

[Zululander]

I am using the following circuit from https://circuitdigest.com/electronic-circuits/ir-transmitter-and-receiver-circuit as an IR Receiver.

When I stand far away and point a TV remote at it and push a button, it LED lights up; hence it appears to be working. However if I get within 1m of the sensor i.e. just stand in front of it without the remote, the LED flickers continually - almost as if a signal is bouncing off me.

It sensor that I am using is not a TS0p1738 but rather the following: https://www.jaycar.co.nz/5mm-infrared-receiver/p/ZD1952.

I therefore have two questions:
1) Why does the LED shine when I stand near the sensor but if I am further away only when pressing the remote.
2) Do I need to make same changes to accommodate the fact that the receiver is a ZD1952?

 

[gophert]

For a start, Q1 needs to be flipped. A PNP should have emitter at higher voltage than collector (and arrow should point in the direction of current flow).

 

[Zululander]

Thanks, I also seemed to have a cold joint as after checking all the connections it came right i.e. it did not activate when I was near. I have also flipped the PNP. Thanks.

 

[Zululander]

Worked the interference out. When I switched of my one Monitor then it did not happen. It was like there is radiation that comes from my monitor and then bounces off of me to the IR receiver as I approach.... not sure if that makes sense.

 

[audioguru]

The people at Circuitdigest are probably students that have not learned electronics yet so they show transistors connected backwards. But the circuit is so simple and the supply voltage is low so it will probably work fine with the backwards transistor.
Maybe your monitor produces IR radiation or heat radiation that bounces off you.

 

[rjenkinsgb]

Many infra-red receiver modules have a metal screening cage around them, so they cannot pick up electrical noise by proximity.
The TSOP1738 that was specified in the schematic has that screening can.
https://electrosome.com/tsop1738-receiver-ir-remote-control/

The IR receiver you are using does not have any screening so it's possible it is sensing stray noise or hum, a bit like an audio amp with an open input?

You could try making a small box or cage out of very fine metal mesh, or foil/shim with a hole at the "lens" part, to fit over the IR receiver device & connect that to the GND pin, so see if that stops it being affected by proximity.

 

[dr pepper]

I've had issues with the tssop range, when I was salvaging one I noticed it had a 100r and 470u filtering it from the power rail, when I tried this it was much better.
Its likely to be electrical noise, as light interference would need to be 38khz, unlikely to come from a monitor.

 

[Nigel Goodwin]

I've had issues with the tssop range, when I was salvaging one I noticed it had a 100r and 470u filtering it from the power rail, when I tried this it was much better.
Its likely to be electrical noise, as light interference would need to be 38khz, unlikely to come from a monitor.

Yes, it's essential to fit the supply decoupling components - there's no need to fit metal screening, devices that require it come with it already fitted - and they were fairly rare anyway.

 

[gophert]

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