Hi Joan,

At 11:22 PM +0200 7/12/01, Joan Ilari wrote:
>Hi to everybody !
>
>...< snip theory >...



>In practice, I get the signal from an electret microphone, I amplify
>it with a couple of transistors and I get a perfect 0-5V signal
>in the output of the last transistor. Up to here the good side of
>practice. But... (there is always a but....)
>
>When I feed this signal in a LM567, the signal which was pristine clear,
>is blurred with noise induced by the 567 (?).

        I guess I don't know what you mean by a distorted signal.

        At any rate my experience follows that of James'. That it's
easily triggered, also that the output likes to oscillate, instead of
providing a nic,e on - siganl there/ off - signal not there, digital
response. My suggestion is to attenuate the signal going into the
'567, until it works somewhat reliably.


>  Under this circumstance
>the tone decoder works but the R value of the oscillator circuit
>in the pll is critical : moving veeeeeryyyyy slightly the trimmer
>makes the tone decoder losing the signal.
>
>I have tried to put decoupling capacitors everywhere, but the problem
>does not disappear. Anybody has any clue ? If I cannot overcome this,
>I will have to get rid of 567s ....


        If possible, try using an ultrasonic tx/rx pair. These will
do an initial frequency discrimination. They may even eliminate the
need for the '567 all together.

Heinz

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics