From: John Woodgate
Subject: Re: Help needed in designing a press-release button to switch on a logic+analog circuit and "explosion" in headphones!
Date: Sat, 19 Oct 2002 13:41:40 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sat, 19 Oct 2002 16:14:13 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Old Lady
wrote (in ) about 'Help
needed in designing a press-release button to switch on a logic+analog
circuit and "explosion" in headphones!', on Sat, 19 Oct 2002:
>I need to press a button (I don't know the exactly English name, but
>is a button that you can press closing the circuit and when you
>release it, it immediately open the circuit again)
Just 'push-button' or 'momentary-contact button'.
>to power on the
>circuit, which starts a digital counter and other few things. When the
>counter reach the status 111, one cmos-AND port should switch off the
>circuit and NO POWER should be drained from the battery, at least
>until one press the button again switching on the circuit.
This is simply a variant of an automatic switch-off circuit. Others have
more experience of these than I do.
>My English isn't so good, but I hope I'm understandable!
Your English is remarkably good. If you hadn't said it wasn't, I would
not have known that you are not a native English speaker
>Another problem is that when I switch on the circuit manually (with a
>classic on-off switch), I ear like an explosion in the headphones
>connected to an LM386 in the analog part of the circuit. Any idea how
>to avoid this?
This is a 'feature' of the LM386 and a number of other audio amplifier
chips. It may be possible to limit the effect by short-circuiting the
input for 1 second or so when you switch on. Again, there are standard
circuits to do this.
> Should I separate the digital and analog grounds?
No, but connect them at one point only.
>to do this?
> I also tried to put a ceramic cap between +12V and GND but
No, that won't do anything. The 'explosion' is due to voltages building
up at the input to the LM386, and inside it.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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