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From: Wanderer<dont@emailme.com>
Newsgroups: sci.electronics.design
Subject: Re: IR detector system, biasing of photo diode
Date: Mon, 28 Oct 2024 11:24:36
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Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
> Hi
> 
> I am working on an IR detector that will guide a robot into a docking 
> station.
> 
> A IR transmitter on the docking station transmits a beam, and 2 IR 
> detectors on the robot detects the beam and lets the robot navigate 
> towards the target. The working distance is a couple of meters.
> 
> I need it to be insensitive to ambient light/sunlight.
> 
> The IR detectors are placed in a tube, to narrow in the beam angle and 
> to avoid sunlight (since it is seldom the sun is actually that low in 
> the horizon)
> 
> The IR transmitter will be modulated with 10kHz (TBD) frequency, low 
> duty cycle. Low duty cycle to be able to drive the LED with high 
> current, frequency modulated so that the receiver can ignore the effect 
> of daylight (DC)
> 

I believe you are looking for a daylight filter circuit.

https://imgbox.com/MOri8WaP

The photodiode converts light into current. The current either comes from the TIA
feedback or the low pass feedback. The low pass feedback keeps the DC photodiode current 
out of the TIA feedback loop. So only the high frequency in the photodiode gets amplified 
a lot and trigger the comparator. TI used to make a part with all this built in. If
you can find that datasheet, there is more detail in there.