Hi Larry,

Just an idea: Take a random number generator routine, send the
result to the PWM register, PWM set to fastest speed. Do this
constantly at a rate of say 2-10kHz. PWM output through RC filter
and AC coupled into audio amplifier. This should give you a kind of
hissing sound, perhaps similar to white noise.

Then all you have to do is modulate the volume to make it rise and
fall like you want. Assuming the random number generator makes
random 8 bit numbers the average should be approx 80h. To reduce
the volume you need to reduce the deviation of the values from 80h.
I would suggest starting with a fixed value of 80h for your PWM
output, treat the 8 bit random number as a signed value (+/-80h),
dvide it by a number depending on the instantaneous volume you
you want, add it to the 80h and that gives you a PWM value.

I don't think I described it very clearly, but if you can decipher the
idea I hope it's useful.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brown@clear.net.nz

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