Countdown Timer 90 Day

[riksworld]

Hi All,

I have been searching around for a timer that counts down from 90 days to 0, I thought about using the common 555 Timer, but I think this wont be reliable enough for this long period of time so it would likely need a crystal.

The circuit would be with 2 leds, one red and one green, the green would be on while the clock was counting down, then the red led would come on after the 90 days have elapsed and the green led goes off, I thought about using either 2 AA or a 9V battery to power this circuit.

Could anyone please point me in the right direction please as im not having much luck with google at the moment.

Thanks to all who replys.

 

[ALERTLINKS]

A small microcontroller like pic12f508 can do it easily if you code it.

 

[BradtheRad]

There is the 4020 14-stage counter IC. It divides by 16,384.

It will accept pulses from a 555. So if you were to adjust a 555 timer to create a pulse every 7.9 minutes, then the 4020 will turn on the red led after it receives 16,384 pulses. That's 90 days.

There's also the 4060 which has an onboard oscillator. You may not need a 555.

http://electronicseveryday.blogspot.com/2009/07/repeating-interval-timer.html

Also the 4024 (divide-by-128) and 4040 (divide-by-4096).

You can cascade these. That way you'd have a shorter pulse length to fine tune.

http://www.kpsec.freeuk.com/components/cmos.htm