D. Schouten wrote:

> There are some 'anti lasergun' LED bars available over here in Holland
> but they cost around Fl.1000,- (= $500). Quite some cash for a couple
> of LEDs and a small matchbox size plastic case.

  Hey, but don't you envy their nerve?

> If some type of modulation is used, maybe it's possible to do it with
> a PIC?

  What (else) would *you* put in a matchbox?  Actually, I'll bet I can
guess - a NE555!

  I was thinking this over the other day.  It's quite straightforward,
except that the "gun" is supposed to have a CPU to detect interference
and alarm on it.

  If they use Doppler, then you want to generate a (sine) waveform
corresponding either to a legal speed, or a ridiculous one.  This is
readily calculable using the Doppler formula, from the frequency (or
wavelength) and the speed, knowing the speed of light.  Just the job for
a 555.

  If they use pulse Lidar, then you need to know (or detect) the
interrogation rate and pattern and generate a closely similar "jitter"
pattern to make their reception meaningless.  A job for a PIC/ AVR etc.
--
  Cheers,
        Paul B.