Anne Ogborn wrote:
>
> Just sweep the laser -
> get a rotating mirror (lots of them around surplus).
> Put a photodiode in front of the laser as it starts it's sweep
> across, and another behind a lense focused on the scene ahead.
> When the laser reaches a given point, it will reflect off the
> scene into the receiver. The time difference is a one to one function
> of the range

I had an idea that I've been trying one of my buddies
(Hi Jules!) to try in his security R&D business.

It goes like this :
You suspend a light circular mirror from a stiff nylon fibre
with the reflective surface pointing down (dia = 3cm)
Stuck to the back of the mirror, there are three small magnets
(pointing up). Above the magnets, there are three small coils
with enough pull to deflect the mirror 45deg. Now you can scan
360deg. with a laser diode pointing upwards. Next to the diode
you have a light dep diode. As you scan the mirror, you record
the light intensity levels in, say 90 steps. These values are
saved in RAM, and the average calculated. The average is used
to normalise the saved values. This set of normalised, saved
values is compared to a pre-saved set of values (RMS sounds OK
for an indication), and any funny values will indicate an object
that shouldn't be there.

You could also use an AGC (Automatic Gain Control) circuit to
keep the measured values useable. For an AGC circuit, I think
the easiest would be to use a MOSFET like a VN10KM (Supertex)
in series with the Ri of an opamp. You need a non-inverting
amplifier for it to work. Stick the light level ouput of the
optical device into Ri. Use an integrated version of the output
to drive the MOSFET.

I probably didn't make any sense...

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