[sdiy] Using audio to trigger CMOS

[Jason Proctor]

sounds like a job for an envelope follower with gate. IIRC, the fine 
Oakley implementation of this involves a rectifier feeding a 
comparator with a variable threshold. there's variable lag on the 
output of the rectifier too so that the comparator doesn't flap all 
the time if the input signal varies a lot in amplitude.

when i had one, it worked like a charm.

hth

>Hey all,
>
>I'm hoping for some help refining a circuit I'm working on that uses 
>an audio signal as a clock to trigger a 4024 Ripple Counter.
>
>The audio signal is a 1/16th note sequence that is meant to 
>represent a square wave i.e. Note On = High (or Mark), Note Off = 
>Low (or Space).
>
>I've got a prototype that uses an AC Coupled gain stage to take the 
>audio input and feeds it into a comparator.
>
>The current version works(ish) minus some problems which I think are 
>down to some ac coupling mistakes and a lack of headroom on my power 
>supply - all of which I think I can sort - but I was wondering if 
>there also needs to be any type of rectification between the gain 
>stage and the comparator?
>
>I can be pretty specific about the type of audio signal that goes in 
>(I'm currently using a PWM square wave with a 90/10 mark/space ratio 
>at a fairly high pitch - which I figured would give the greatest 
>ratio of High to Low signal when the Note was 'on') - I'm not 
>expecting to get a square wave trigger out of a guitar input for 
>example - but I'd like the circuit to be as safe and reliable as 
>possible.
>
>Any advice? Appreciated as always
>
>J
>
>
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