Switch off Circuit?

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Hi

I am trying to figure out how switches in modern devices work. It seems to me they operate on some kind of momentary push button system. But I cant figure it out- especially if battery life is an issue.

Up to now I have been using these clunky flip switches which disconnect the battery from the circuit.

If someone can please point me in the right direction to have a small profile water-proof switch- I would greately appreciate it?

Thank you in advance.
a.

[PCM programmer]

I'm not sure what you want. Do you want help in selecting a push-
button switch, or do you want a description of an "auto-off" circuit ?
In other words, the product will shut itself off, after a certain amount
of time, or non-usage.

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Hi PCM Programmer

I am looking for the methodology/ circuit/ software (?) (I dont really know what actually) that can implement a switch for the entire circuit. i.e. when you press it the circuit turns on, when you press it again it shuts down.
The switch is very common on most modern devices I notice.

I am not sure how its done (up to now I have been using a simple but clunky switch which actually breaks the current flow from the battery).

Thank you
a.

[PCM programmer]

I've done one product that used a pushbutton to turn on the power.
This was done with T.I. switching voltage regulator chip, the TPS61107.
This chip takes two AA batteries for the input power and puts out +3.3v
and another voltage. It has a specific pin that's intended to be
connected to a pushbutton. When that pin goes to ground, the chip
will turn on and put out +3.3v. The PIC then receives the +3.3v and
turns on. The PIC then sets one of its pins to a high level, and that
signal goes back to the Enable pin on the TPS61107. This is a different
pin than the pushbutton pin. As long as the enable pin is held high by
the PIC, the TPS61107 will continue to put out +3.3v, even if the push-
button is released.

In our design, I think we had the PIC turn off the power supply chip
if no buttons had been pushed for 30 minutes, or something like that.
You could easily change the PIC code so that it checked the button,
and if it was pressed again, then the Enable signal could be set low,
and this would turn off the power supply chip.

[Ttelmah]

This type of switching, can be done using transistors, or simple logic. There are probably a hundred 'variants', that will give the required effect. A couple of CMOS gates, will allow a latch to be built, arranged so that when you apply power through a button, it always 'wakes' in one state, normally by using a charged capacitor to toggle a line, but if already awake, and you make the same connection, it toggles 'off'. Using a capacitor, helps prevent keybounce from causing problems. Most of the commercial systems using this, will have the logic implemented inside their own custom chips. I remember building my first version of this, based on the MC4001, a diode, couple of resistors and a capacitor, about thirty years ago. Once this logic circuit is 'awake', it is only a matter of using a suitable power FET to turn on the main circuit.
Have a look at the article CA472837, on Edn, which shows a basic transistor circuit to do this for low voltages, which can easily be modified for 5v operation.

Best Wishes

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Hi

Thank you PCM Programmer and Ttelmah.
I have implemented something very similar to what both of you suggest!

Thank you and
Regards
a.