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Construction of a Timer Switch

  1. Mar 8, 2012 #1
    Hi,

    I'd like to do a small design project. When I sleep, I switch on my mosquito repellant for about 8 hours. Sometimes I forget switching it off too. Such long durations are little poisonous and generally not required.

    What I plan to do is to make a timer with a dial from 0 min to 60 min (like a clock). When the user sets a value (say 15), I want to switch the repellant on for 15 mins, off for the next 15 mins, on again for 15 mins, like that ..

    Kindly let me know how I could do the same. Final device should be mounted on the switchboard.

    Thanks,
    Chaitanya
     
  2. jcsd
  3. Mar 8, 2012 #2

    vk6kro

    User Avatar
    Science Advisor

    Do you have any experience at using microprocessors or building circuits using integrated circuits, without a printed circuit board?

    Do you intend to use this with mains voltages?

    One way is to use a micro like a Picaxe chip. This is a very easy way to do this.
    You would just read an input voltage. relate this to the time required.
    Make one pin of the chip go to 5 volts.
    Wait the required time set by the input voltage.
    Make the same pin 0 volts.
    Wait the required time set by the input voltage.
    Make one pin of the chip go to 5 volts.
    and so on.

    Another way is to make an oscillator that covers about 130 Hz to 1500 Hz.
    Use a divider that divides by 16384
    This would give a square wave whose period varied from 120 minutes (60 on, 60 off) to about 11 minutes (5.5 on and 5.5 off)

    These two circuits give a voltage out which would be used to switch a transistor which switches a relay.
    This would then turn on your mosquito repeller.
    If it is toxic, why don't you use flyscreens on the windows, or mosquito netting over your bed?

    However, if you have little experience and this does use mains voltages, you should look for a commercial product or seek help from someone who could guide you to do this safely.
     
  4. Mar 8, 2012 #3
    Thanks! I'll see what I can do. :)
     
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