slippyr4 wrote:
> I need to design a circuit such that a signal from a PIC will cause a
> beep signal. My definition of a beep signal is aproximately 1KHz,
> close to a sine wave, and in the region of 75ms long. I need the
> output signal to be audio "line level" - which although poorly defined
> seems generally to be regarded at 1V peak to peak, AC, driven by a
> lowish impedance. The audio signal I generate needs to connect to a
> line in jack on a tape recorder. The whole circuit runs in a car - so
> it's a noisy environment. I'm not looking for Hi-Fi quality audio, but
> it does need to be reasonable.
>
>   
Jon,
Olin's low pass filter on the output of a PIC is a great idea especially 
cause you can control the
length of the beep with firmware.

I have used different sine wave oscillators in the past such as the 
Twin-T ( www.discovercircuits.com/Andy/Twin-Toscillator.pdf  )
or better yet ( 
http://home.att.net/~theremin1/Circuit_Library/twin_t_oscillator.html 
).  This is a really good one. And tones from Twin-Ts have pretty low
harmonic content so they sound better is many applications.

You may want a buffer amp on the output and you need a way to turn the 
beep on and off.  This is why Olin's solution is good.
Carey

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