photodiode with op amp ..#2


Joined Jan 12, 2015
Hai @KeithWalker,
I am also using same circuit. It's normally working fine. But easily affect by direct sunlight and GLS Bulbs.
I tried to avoid this issues. But everything get fail. Do you have a any idea to resolve this issue...

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Any light source that contains energy in the IR range of frequencies will excite the device and activate the circuit.

You could make the device sensitive to some sentinel signal, a sequence of pulses, that is you could modulate the light coming from your actual source, natural light will carry no modulation signal and thus have no effect. This is exactly how IR remote controllers work for TV etc.



Joined Jul 10, 2017
Making the photo-detecter more directional will help. You can do that by mounting it in a tube with dark, non-reflective interior walls.
Using a modulated system will improve the sensitivity and reduce the effect of external radiation sources as ApacheKid mentioned. The receiver will be a capacitively coupled AC amplifier and so it will reject any DC offsets caused by changing background radiation.


Joined Jan 12, 2015
I was actually playing around with some IR diodes recently, first time in years that I've done anything with breadboard. It was interesting and I had a scope and signal generator hooked up so I was able to experiment a little. Eventually I made a crude gizmo (well, it was all on the breadboard) to measure the speed of rotation of a radiometer.

I think under intense flashlight (very bright, even gets warm, LED flashlight) I saw just under 1,000 RPM (taking into account the four fins it has etc).

In fact it was like a day before I discovered that the photodiode must be operated in reverse bias, so much for assuming things.

Audioguru again

Joined Oct 21, 2019
A photodiode can be operated with reverse bias voltage so that it leaks current when it is activated with light.
OR a photodiode can be with no bias voltage and used as a solar cell to produce a low amount of voltage and current.