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From: Hul Tytus <ht@panix.com>
Newsgroups: sci.electronics.design
Subject: IR detector again
Date: Mon, 11 Nov 2024 16:31:56 -0000 (UTC)
Organization: PANIX Public Access Internet and UNIX, NYC
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   Klaus, you might mount the tubes at a slight outward angle. When one is 
saturated steer toward the other.
   R V Jones' "Most Secret War", which Phil mentioned, describes a German 
navigational aide that quided aircraft on landing. Two beams were lined 
up with the runway but diverging a few degrees. The pilot approached 
keeping the reception of the beams equal.
   Your approach has a higher frequency with reciever/transmiter 
altered some. All in all though, suprisingly similar.

Hul


>   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). If 
> the LED on the docking station has higher radiant intensity at the point 
> of the robot (2 meters away) than possible IR from sunlight, then that 
> would be perfect.
> 
> Example of transmitter:
> 	www.vishay.com/docs/83398/vsmy2850.pdf
> 
> Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, 
> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam 
> that has higher output than sunlight seems unlikely.
> 
> I would use a IR phototransistor at 850nm, something like this:
> 	www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/
> OP505-506-535-705.pdf
>	
> Or a photo diode:
> 	https://docs.rs-online.com/9f58/0900766b816d8a09.pdf
>
>   Fed from reverse 3.3V and into a transimpedance amplifier to boost the 
> signal with bandpass filter. One can get digital IR detector used in a 
> remote control systems:
>	www.vishay.com/docs/82491/tsop382.pdf
>
>  It has AGC, but digital output. I need analog output to be able to zero 
> in on the transmitter beam. I have been looking for IR detectors that has 
> the analog output, not just the digital, but have not found any. If the 
> photodiode detector is subjected to sunlight, I am guessing I would need 
> very high gain on the 10kHz modulation frequency to pick up the burried 
> signal in the DC from sunlight. How do I best bias the photo diode for 
> optimum detection of the 10kHz signal while being immune to the ambient 
> sunlight? I have chosen 850nm which seems to be a good wavelength. The 
> spectrum at sea level has some dips due to water absorption.
>	https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%
> 20absorption.png
>	
> Seems like 750nm would be better, since then the IR from the sun is 
> lower, but does reduced the effective range of the system during 
> fog/rain. Probably that's why these system do not use 750nm
>
> Other considerations?