From: gsulliva@enuxha.eas.asu.edu (Glenn A Sullivan)
Subject: Re: Long distance IR detection
Summary: More facts on LONG DISTANCE IR DETECTION
Organization: Arizona State University
Distribution:  na
Lines: 34

jvannes@vms.macc.wisc.edu writes:....
> >I designed and built hardware in 1988 that would output a logic level (from
> >a 567 tone detector) upon detecting a 500 microwatt LED 28 feet away.
> >Used a Motorola MRD360, biased linearly  in a DC-feedback loop to servo out
> >variations in sunlight (and 60Hz from lights). Used no lenses.
> >Allen Sullivan
> I would be interested in knowing more about the sensing hardware.  What did
> you use for the detector?  Could you detect the angle of location, or did
> the system simply respond to the presence of the transmitter in the sensors
> field of view?
 
Phototransistor-> X100 -> X100 -> NE567
with 330Kohm              Limiter 
feedback to base                  
to control operating point (I expect this really hurts Noise Figure! Any
comments from Phototransistor experts?)

We intended to use this atop a stepper motor, to provide headings to the
beacons. The plan was to have 3 or 4 beacons, of different frequencies, in 
each room, and tell the 567 what frequency to phase-lock to. We did not do so.
One challenge was that the available stepper had 8 degree steps!
Knowing the headings to each beacon, we would have used the surveyor 
technique of RESECTION to determine robot location. (No, I ain't going to
explain resection over the net.)

Given hindsight, I would digitize the amplified output of the self-nulling
phototransistor circuit, and correlate in-phase & quadrature square-waves at
the several expected frequencies, to extract AMPLITUDE of each beacon.
By doing this at the numerous steps, even with  8 degree steps, with knowledge
of the angular response of the phototransistor, you SHOULD be able to
rather more accurately determine the heading to each beacon.
Allen Sullivan


