external interupt from slight change in voltage

I have an attiny25 measuring a voltage value from a pot every 5 seconds. So basically the attiny sleeps and wakes up every 5 seconds to measure the voltage, if it hasn't changed it goes back to sleep. What I would like to know is, can my attiny perminantly sleep and only wakeup once the voltage value does change? That way I won't have to wakeup every 5 seconds to check it? I'm guessing en external interupt can only be a high or a low and analog values will not work? If that is true then is there no way I can use a comparator chip or something to create a high when the voltage changes?

The whole goal of this is to minimise battery power consumption. I need to get the attiny to flash a green LED every 5 seconds until movement of the pot is detected then it must flash a red LED. The problem is, once there is movement on the pot the red light must immediately flash, it must not wait 5 seconds before it flashes red.

One of us should really read the Atmega datasheet for the attiny25.

You first, I'm lazy :slight_smile:

...R

can my attiny perminantly sleep and only wakeup once the voltage value does change?

If it can, this:

I need to get the attiny to flash a green LED every 5 seconds

isn't going to happen.

What is this voltage coming from? Why can't it power the attiny?

calvingloster:
The problem is, once there is movement on the pot the red light must immediately flash, ...

Define "immediately". Would 100 mS be close enough? 10 mS? 1 mS?

Yes 100ms would be fine. Not more than 300ms

PaulS:

can my attiny perminantly sleep and only wakeup once the voltage value does change?

If it can, this:

I need to get the attiny to flash a green LED every 5 seconds

isn't going to happen.

What is this voltage coming from? Why can't it power the attiny?

Ok I get what you are saying, the voltage is coming from a potentiometer.

3 AA batteries will be used to power the Attiny and the pot.

Well it seems to me the simple thing is to set up a watchdog timer to wake you every 250 mS, check the potentiometer and note any changes. Meanwhile every 20 times you wake (ie. 5 seconds) you can flash the LED.

See here for saving power and using the watchdog:

"Sketch I" on that page shows flashing an LED every second, so you could do something very similar to that.

I see what your saying, I will need the attiny to wake up to flash the LED every 5 seconds anyways. I was trying to figure out a way to flash the red LED "imediately" when a change in voltage occurs, but I'm guessing the attiny will have to wakeup every 250ms to measure this. Although battery power consumption will be increased greatly then. I will need the attiny to run on 3AA batteries for about 1year or as close to a year as possible. The longer the better

The LEDs are going to use a lot more power than the waking up. I have a gadget I made over a year ago that is still going strong:

That uses 3 x AA batteries.

That shows some other techniques, like sleeping during the ADC conversion.

My advice is to choose the batteries wisely. NiMh are notorious for fast self-discharge. Use non-rechargeable, or maybe Lithium ones.