How will change the functionality of this circuit the missing of R5 and R6 ?

On 10/6/06, Olin Lathrop <olin_piclist@embedinc.com> wrote:
> 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.
>
> Drive the attached circuit from a 0-5V PIC pin.  Use a 500uS periodic
> interrupt to toggle all the pins you want producing the 1KHz tone.  Set all
> the pins that are supposed to be quiet to high impedence.  I think the tone
> purity will be good enough.  I haven't figured out the exact resulting
> amplitude, but I think it will be within acceptable range of a audio line
> input.
>
>
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