I breadboarded the design ya'll helped me 
with previously and everything works perfectly! 
Thankyou!.. Now on to my next challenge.. it is 
stretching my mental capacities so far and should give 
me experience with the a/d converter if it can work
like I think it might. This is a hobby circuit.. nothing 
professional here. 

I have a servo mounted in a fake skull that can move
the skull's jaw. There are several non PIC based circuits 
out there now to do this but they are simple threshold circuits. 
If the circuit detects an audio signal it tells the servo
to move as rapidly as possible to open the jaw until sound
is not detected and it closes the jaw as rapidly as possible. 
While this works..its not very realistic. Its doesn't account 
for the fact that a loud sound should open the jaw faster
and in turn, further then a softer sound. 

It seems that a PIC with an a/d converter and ability to drive a 
servo using PWM could be a good solution to this. 

Basically what I want to do is sample a line level audio 
signal pretty rapidly and based on the presence of sound
move the servo to open the jaw at a rate based on the 
amplitude of the sound, so a louder sound will cause the servo 
to move quicker to a location and hence further then a
softer sound which will cause the servo to move slower 
and less distance then the louder sound. So if it screams 
it will rapidly move the jaw open, and a whisper will just 
cause a tiny jaw movement despite the duration of the sound. 

After doing some research on the net it looks like I will 
need to use some circuitry to cleanup the audio signal 
since the a/d converter bases its comparisons on 0 to 
Vdd and as I understand it, audio signals aren't 0 to 5 volts. 

Any ideas how I can do what I want to do? I know this project 
is probably over my skill level, but ya don't learn unless you 
push yourself. How would you do it? I don't think the actual 
circuit is the big issue (except for the audio cleanup part - no 
clue there) since there are plenty of examples of driving servos 
with PICS on the net. My biggest hurdle is using the a/d converter 
to figure out if sound is present and the amplitude of it and 
creating a direction and rate at which to move the servo.

Thanks, 
Mike


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