Latching Circuit/ Auto off

Other Hardware General Electronics
1

Hi,

I'm working on a project that will use a membrane keypad to control all functions of the project.

I need a latching circuit to control power. To turn power on, a button on the keypad needs to be pushed. The circuit needs to be turned off by using a pin on the Arduino. The Arduino is powered by 5V from a boosted 3.7V Lipo battery. Ideally the latched circuit can tolerate 1 amp.

I came across this circuit, http://www.circuitpop.com/pic2.html. Is this circuit suitable? I will need to buy in these parts especially if need be.

It'll be great if anyone can offer some advice on this. I'm very new to circuits.

Cheers

2

There are many variation of the power button design you shared.

A nice explanation of "how they work" is done here: http://www.eevblog.com/2012/03/30/eevblog-262-worlds-simplest-soft-latching-power-switch-circuit/

Though, he does not share much about using a signal to turn it off.

Simplest one I know of:
http://img36.imageshack.us/img36/420/davidlw.png

For me personally, it's just simpler to buy one of these. Pololu Pushbutton Power Switch SV (old version)

It meets your requirements since it has a logic level shutoff pin.

3

Have you considered using a standalone atmega328 chip (which you can get ready-assembled on a board with the crystal if you want) and running it directly from 3.7V? Then you wouldn't need either the power supply voltage booster or the power supply switch, because you can put the chip in power-down mode to turn it off, and wake it up again when certain of the membrane keys are pressed.

4

Two CMOS NOR gates make a flip-flop to control a p-channel MOSFET power switch.
A push button and pull-down resistor form the turn-on circuit, and the load
can pull the other input high to switch it off again. The supply voltage (and MOSFET)
is assumed logic-level.

5

Thanks for your responses.

I am actually using a standalone Atmega2560 for this circuit.

MarkT: Are you able to provide a circuit example of this setup? It would be very much appreciated.

Cheers

6

What is the reason that you don't run the atmega2560 directly from the 3.7V supply? Do you need the 5V to power something else?

7

dc42:

You're completely correct. I didn't think that i could power it by 3.7V until i checked out the datasheet more thoroughly. Thanks!