Re: IR detector system, biasing of photo diode

On 10/29/2024 5:02 AM, Don Y wrote:

In LORAN, the carrier was modulated with a specific envelope
(as well as a pulse code pattern) to let the receiver identify
a specific reference point on the carrier.  (because multiple
signal sources could be present in a given geographical area)

Actually, an audio frequency version of LORAN could work in this
application!  But, would require more "set up" of the arena.
Three transmitters would be placed at fixed locations (there are
some concerns over the optimal geometry but there is also a lot
of variability tolerated).  The "robot" would have a single
omnidirectional receiver (microphone/ultrasonic transducer, etc).
The location of the base would be known a priori (along with the
locations of the three transmitters).
One transmitter would be designated as the "Master".  It would
emit an omnidirectional pulse "periodically".  Each of the remaining
two transmitters would emit pulses at fixed delays from that master
pulse.  In LORAN, this is done by *receiving* the master's pulse
(which takes time to arrive proportional to the distance from the
master) and adding a fixed "coding delay".  But, on a small physical
scale, this could be accomplished with any other synchronization
mechanism (including hard-wired).
[Each of the other (two) stations ("slaves") has a different coding
delay so the signals from the master and slaves arrive separated
in time from each other.]
The robot detects the master's pulse at a particular time.  And, the
pulses from the two slaves at some time after that.
The difference, in time, between master and each slave defines
a hyperbolic curve in 2D space.  The intersection of the two
curves (master-to-slave-1 and master-to-slave-2) defines the
position of the robot in that space.
At 1100ft/sec, one could resolve a foot with a crude timebase of
1KHz.  If you can count 10KHz, you can resolve an inch.  100KHz
and you're at an eighth of an inch.  (there is some hand-waving, here,
as there is a geometric dilution of precision, depending on
where on each hyperbola the robot happens to be)
With positional information, you could actually describe a *specific*
path to be followed to the base to avoid fixed obstacles in the
arena.