On Mon, 11 Nov 2024, Hul Tytus wrote.
It's the fly's ear problem. The fly's ear does this mechanically. You take the sum and the difference of two signals. If the sum is high enough you have signal. Then the difference tells you the direction. You try to zero the difference while maintaining the sum to fly straight at the signal.
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:
>formatting link
>
> 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:
>formatting link
> OP505-506-535-705.pdf
>
> Or a photo diode:
>formatting link
> 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:
>formatting link
>
> 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.
>formatting link20absorption.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?
In radar, this is called Monopulse.
.
Joe Gwinn
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