Toggle power with menbrane switch

%#&$. 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.

Ed

correct

The spec sheet says that simply connecting OUT to SHDN will turn the regulator on.

I've posted (I think) my updated schematic to alt.binaries.schematics.electronic.

Ed, It looks like you have the 3V going _through_ C1...is that correct? I think your explaination will work, I just can't figure out the schematic. j

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:

I added a resistor - it allows the cap to discharge when the button is released.

Ed

^^^^^ left

Depends on whether you're in the US or the UK...;-)

Bob M.