Year long timer

Discussion in 'The Projects Forum' started by JDCrow, Aug 20, 2010.

  1. JDCrow

    Thread Starter New Member

    Aug 20, 2010
    1
    0
    I am going to construct an ultra low power timer that will countdown for up to two years and still have enough power to drive a small relay at the end of the countdown. It needs to be portable, but battery space will be substantial. The project is a timed lock. The counter's primary function would be to count down a very extended amount of time up to two years and then be able to drive a secondary power source and low power locking mechanism.

    If this purely electronic/mechanical approach isn't reasonable does anyone happen to know a good alternative combinational approach to long term ultra low power countdowns? I have even been trying to find chemical processes that could possibly slowly disentegrate a sample material and suddenly allow full current flow to open the locking mechanism when the sample is fully disentegrated. Any ideas regard these types of electronic/chemical processes or other long term electronic/mechanical processes are welcome.

    Let me know if you guys have any insights or suggestions.

    Thanks everyone
     
  2. sage.radachowsky

    Member

    May 11, 2010
    241
    38
    I would feel most comfortable with an electronics-based solution.

    I'd use a low-power microcontroller with a crystal for timekeeping. The MSP430, for example, can run a 32768 Hz crystal on about 2 or 3 uW. At that rate of power consumption, it can run for a decade on a couple D cells easily, so long as the cells don't just totally die due to calender life limitations. In other words, the power used by a properly made microcontroller circuit with real time clock is less than the self-discharge rate of most batteries.

    If you want this thing to be really failsafe, then I would set it up so that you have multiple timers, any of which can unlock the thing when it triggers, and each running on its own pair of D cells or similar power source.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    An alk. D cell @ about 19,500 mAh should supply 1.1 mA for 2 years, which could drive two cascaded 4060's with ample reserve. Time tolerance not stated by PO.
     
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