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From: Jan-Hinnerk Reichert
Subject: Re: Electronic On-Off Switch Using Thyristor?
Date: Mon, 02 Sep 2002 14:58:07 +0200
NNTP-Posting-Host: b076138.adsl.hansenet.de (126.96.36.199)
Geraldo Sazias wrote:
> I'm buidling a portable MP3 player but I want an electronic on-off switch
> controlled by the 'Play' button, just like in most portable CD players. I
> was thinking of using a TRIAC/Thyristor which is ignited by the play
> button (momentary
> contact) and which turns-on power to all circuitry. The play button is
> also connected to an I/O port on the MCU.
> Is this a good idea or are there some other more preferable solutions?
> Thanks for the advice.
First you have to decide between two basic principles:
- you can cut power to the whole circuit
- you can have some low current (few uA) thing on power all the time.
If you don't have a dedicated power switch you're already a bit into the
You must define a clear line between those parts under constant power and
those switched, because strange things happen if you have 5V on an input
pin of an unpowered device. (the device is than powered through the
I don't know what hardware you are using, but some microcontrollers (like
AVR, don't know about PIC) have low current SLEEP-modes.
So can you just let the microcontroller switch power off via some MOSFET,
relais or thyristor (take care of transients).
Put all I/O-lines low (don't leave them floating).
And put the processor to deep hibernation (just remember to enable some
wakeup on the PLAY-key)
You could also think about connecting PLAY to reset
You must also take care that no pull-ups are connected to the unswitched
If your design allows you could also decide to leave some other parts on
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