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Battery Operated Timer

Discussion in 'Power Electronics' started by Jamie, Apr 6, 2010.

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  1. Jamie


    Apr 5, 2010
    I have a battery powered automatic aerosol dispenser. It is similar to an automatic aerosol dispenser you might find in public toilets except mine is used to dispense mosquito repellent. It actuates the repellent every 15 minutes, 24 hours per day, 7 day a week etc.

    I would like to modify the dispenser to include a timer or light sensor to limit the time the dispenser operates. Does a battery powered timer switch or light sensor exist that I could integrate into the device? If not, I would appreciate suggestions on how to make a battery operated timer switch - which would actually be my preference.

    The dispenser operates on two "D" size batteries.

    Thanks -
  2. neon


    Oct 21, 2006
    You could buy a photocell to actually cut off the circuit totally when there is light. I don't have a dispenser per say to do that since garlic is very cheap and last for months.I travel to the tropic every year and garlic odor smell deposit works guarantee. try it. no dispenser just crush it.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Curiously enough, I have a similar unit (except it operates from 2 AA cells and has a timing of 13 minutes between sprays). I was planning to do a similar thing except I wanted 2 sprays per day, approx 12 hours apart, and I considered using a sensor to try to keep it synchronised with daylight (for no other reason than it sounded like an interesting problem).

    Long duration timers are a problem. One approach is to use a faster oscillator and a divider (which is what I'd suggest in your case). For very long periods, especially where some "thinking" is required, a uC may be an alternative. At slow clock speeds, many microcontrollers draw very little current.

    If you just want to turn the device on and off with daylight, a simple option is a photocell connected to a mosfet which turns the circuit on only when there's daylight. You'd want to have +ve feedback so it turns on and off quickly, and you may need to play about with it until the trigger point is right. The sensor would have to be somewhere that prevented accidental operation by people passing or lights, etc.
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