How can I attach four separate buttons to a single interrupt?

First of, if you are driving the bottom of a button low and the top is to another pin that is an input with a pull up, then I would simply look for that pin going low and use it to trigger the interrupt.

Now if you want the MPU to be asleep then output all bottom pins of the switches to low so that any one of them being pressed will pull the input pin low, then the ISR will scan the pins quickly by having only one button low at a time to determine the one that is pressed

You can't balance a pull up on one side of a switch and a pull down on the other and hope they're going to swap states when the button is pressed, at best the voltage will go to a mid and undetermined voltage which is not good. you need a solid pull to zero volts by using the pin as an output

I hope that helps you out

There are several ways to solve this - if I understand it correctly.

One way is to use double pole switches, where one pole on each switch drives a corresponding button pin, and the other poles are all connected in parallel to the wake pin.

Another way is to use diodes so that button pins are only affected by one button, but the wake pin is sensitive to all buttons.

Doug

Ah, its been so long, YES dougw, that is a much simpler option

I like the dougw proposal. Making an and gate with diodes with an internal pull-up for the interrupt input, and each katode to each input.

Just be carefull of a very important thing, Vf of the diode must be less than 0.3Vcc, it should not be a problem for 5V or even 3.3V, but I can be for lower voltages.

Isn't that an or gate?

Hi Jan

If you use internal pull-up resistors, you make the interrupt when input is low, the normal status for the inputs is high, and as soon as you have a low at any input, you have a low in the interrupt:

1  1 -> 1

1  0 -> 0

0  1 -> 0

0  0 -> 0

That's an and gate.

You can use diodes in a or-gate way, connecting all the katodes to the interrupt pin (and each anode to each input pin), but then the interurpt should be active by high, instead of low, and you have to use external pull down resistors, instead of internal pull-up, of course, the inputs should work also with pull down resistors in this case, where as soon as you get a high at any input, you will have a high at the interrupt.

0 0 -> 0

0 1 -> 1

1 0 -> 1

1 1 -> 1

That's an or gate

I know I am not a very good at explaning.

Maybe an image it is better:

Diode Logic Gates

You are correct.

I like the double-pole switch idea, but I like the diode idea better.

Is this what you were talking about?

I labeled the lines that would connect to the microcontroller

The junction between each switch and its diode would go to an input pin, that pin would be set with a pullup. Int0 would also be an input with pullup.

When any button is pressed, the respective pin would also go low but through the diodes, the INT0 pin will also go low. Well mostly low less the diode drop, but still enough to be registered as a zero and trigger the interrupt