Will this work to toggle power using a membrane switch?
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To power up: The PWR button brings the SHDN button high, turning everything on. The processor keeps the SHDN pin high after after it boots up. To power down: Monitor the PWR button, set the SHDN pin low when it is pressed. Question. I need the diode to separate the "keep on" voltage from the PWR button signal. I'm not sure I have this correct.
%#&$. Sorry! I though they didn't make you do that! Of course I'm away from my normal PC now and can't post a proper message. Anyway...pls try this link:
I think "The PWR button brings the SHDN button high" should read "The PWR button brings the SHDN *pin* high"
It won't work as you have drawn it. With everything off, the out pin will be low. Pressing the pwr button will connect low to SHDN - the opposite of what you need. I think you need to do something like this:
Sequence from off to on: All off, press power, SHDN goes +, 5V turns on, CPU turns on. The power on reset condition must put + on SHDN. A power on reset routine must loop until mon goes -, meaning the power button has been released. Once mon goes -, the main program runs.
Sequence from on to off: Press power, mon goes +, program reads mon and toggles SHDN low. CPU continues to run briefly via C2 after MAX1675 shuts down, to hold the SHDN pin - long enough for C1 to be discharged.
I suppose it's symantics - the 3V isn't "going _through_ C1" per se. You get a pulse charging C1, then the 3V is blocked.
The cap is there to give you a + pulse to get things started and to get things stopped. But I drew it wrong - no discharge path. Grumble. The cap needs a discharge path on the right:
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