Steve Hardy wrote:
>
> I have recently made a PIC-powered sonar, and thought I might share the
> experience.  Of course, there are commercial units (e.g. Polaroid),
> but then I didn't have one of these in my junk-box...

Thanks for sharing this, it was truly informative. :)

Have you considered using a *primitive* adaptive filter? Say, for
instance, you transmit sixteen cycles. In your RX amplifier, you
set an AGC to keep the duty cycle of the incoming data at around 50%
(The duty cycle that you transmitted). Shift the incoming data into
two bytes of RAM. Compare (XOR) the databytes with the pattern you
transmitted (in this case 10101010 10101010). This will give you a
score of 1 - 16. At the point of highest score, the measurement is
complete.

Using a pseudo random pattern will give better results with the
correlation though.

This will mean that you can get away without the A/D, and that you
should be able to lock onto the carrier phase itself. Using the
longest code you can given your 10Mhz clockrate, the correlation
should reject most noise sources.

If you decide to give it a try, please let us know how it turned out.

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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