I would like to be able to do the same thing but the frequency I want to
detect is much lower and the burst longer. I would like to be able to detect
the hang-up tone on a telephone line. By this I mean the tone you hear when
the other party hangs up. I was thinking of using a dedicated 12C508/9 and
just measuring the time between peaks and troughs. How does that sound ?

Steve Ridley
Blue Ocean Telecommunications
Sydney,  Australia

-----Original Message-----
From: Ing. Marcelo Fornaso <mfornaso@infovia.com.ar>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, September 06, 1999 8:14 AM
Subject: 100Khz filter?


>Hi Pic addicts!
>Can anyone of you think about a piece of code for 12c508/9, to be able to
>detect and 'filter' a 1ms burst of 100khz (TTL levels), without any added
>hardware?
>Of course I can use an active filter and a rectifier-detector, or a tone
>decoder, but the challenge is to detect the burst only by software,
>filtering the present noise.
>I'm still evaluating to consider the count of transitions averaged over
>time, or perhaps some kind of digital-filter principle (IIR-FIR?).
>I've got some experience working with Pics (my serial output 16F84-based
>video frame grabber is working just fine), but I've read such a brilliant
>ideas around here that any suggestion will be truly appreciated.
>
>Have a nice weekend.
>
>Marcelo Fornaso
>from Argentina
>marcelo@syyyysameri.com  (write 'sysameri')
>