Long time countdown timer

[abeness]

Dear friends
I am just a user form Greece and this is the first time that I post to your forum :)

I would like to help me with something, and I hope to post it in the correct subforoum
I am looking for a not expensive long time countdown timer.
When I say long time, I mean about thirty (30) months

I would like to have a couple of numeral displays, but I do not care the precision very much.
The display it does not matter if points the months or the weeks.

I can create one if I had the circuit, but I have not the knowledge to make a programmed if that needs.
The cost that I can give is about 30 – 40 $

Thank you very much for your time

[kwinn]

I am not aware of any commercial products to do that but here are a lot of inexpensive microcontrollers that could be programmed to do what you want.

[tonyp12]

Hard to find, and probably would have to order from China.
http://www.alibaba.com/product-gs/278469672/led_timer_clock.html
http://www.alibaba.com/product-gs/402070054/Great_countdown_timer.html

[homosapien]

PM sent, check your PM inbox.

[Loopy Byteloose]

Well, this could be done with a BasicStamp - but the biggest problem is providing a power source that doesn't go down for the whole period of time.

Why so?
Generally, the microcontrollers are clocked in megahertz. The faster they go, the more power they require. So a couple of AA batteries won't last long enough.

It would help to slow the microcontroller down to 32Khz with a clock crystal, but you would still be running rather quickly as you would have to divide by 32000 or so just to get one second and it appears you want to count days.

What is the better approach?
Have a BasicStamp or Propeller work with a Real Time Clock chip that has its own internal battery and just provide a read out. There are several choices for doing this and it eliminates the hazard of an interrupted power supply turning off the clock.

If you must stay in the $30-40 budget, a Propeller chip can do it as it is less than $10USD. And you will find examples that support various RTC chips.

Parallax has the DS1302 chip for $5 but you would have to build a board. Sparkfun has the DS1307 chip on a board that will run for 9 years for about $16.00USD and make assembly much easier. It is also an update of the older DS1302 with better features.

The Propeller OBEX has code for the DS1307, so I would go with the Propeller and a Sparkfun board for ease of entry.