Andy Faulkner wrote:
>
> What is all this phase stuff you keep talking about.
>
> Are you meaning that if you send a square wave
> modulation down a lasers beam buy modulation, the
> further you get away you get a change in the frequency
> of the modulation.

Hi Andy, switch the laser on/off at 1MHz. Sense
the reflected signal with a high gain amp with no phase
shift (someone suggested FM radio chip).
The reflected signal travels twice the distance.
Speed of light delay (time of flight) causes a phase shift
between the transmitted squarewave and received squarewave.

You can simply AND or XOR (etc) the two squarewaves to give
a pwm signal that depends on distance.
Changing the modulated frequency affects the possible
max range of the system.

People have suggested problems with isolating the receiver
amp from the transimtter RF noise. Also sensing phase
using the "hump" of the received signal, not the zero
crossing point. I have a design mostly finished for this
technique for hobby robotics and have learned a bit
from the discussion here so far. Thanks everyone! :o)
-Roman

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