Building a Countdown Timer with a 555

[tenacity2986]

Im trying to do just that, that is build a timer that countsdown accurately to the minute. Ideally this device should have a range of about 5 second countdowns to 36 hour countdown. I'd like to add a 7-segment LED display wired to count as well but I am not sure I think i can do that with a 555 without a crystal oscillator. What I am thinking might work is using a crystal oscillator in tandem with a microcontroller that will know the number of clockcycles a second are before decrementing the value on the LED display where at T=0, it should send a high voltage pulse to the output terminals, preferably high enough power such that it can accommodate turning a small dc motor on. Thanks for your help and valuable insight.

 

[Pumblechook]

Much better to use a 4060 chip and a watch crystal. Accurate to a fraction of a second without any adjustment.

 

[tenacity2986]

Thanks for the honest feedback, however where can I find these types of parts? I've found so many different brands of ICs with so many specs most of which mean absolutely nothing as of now to me... What should i be looking for when purchasing a viable IC for my application?

 

[Pumblechook]

DC4060... Part of the CMOS range.

http://www.google.co.uk/search?hl=en&q=CD4060&btnG=Google+Search&meta=

Maplin,, Rapid or CPC in Britain.