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Question about how to build a timed switch

Discussion in 'Electronic Basics' started by Igor Carajo, Dec 4, 2003.

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  1. Igor Carajo

    Igor Carajo Guest

    Hi,

    I'm not a EE or an electronics expert and I'm hoping that somebody
    will be able to help me. Did you notice when you get in your car and
    you put the key in the ignition, you might get a "fasten seatbelt"
    light in your dashboard for several seconds and then it goes out?
    Well, I need some sort of timer that will do exactly that: close a
    circuit when you give it power, for 10 seconds or so, then open the
    circuit. If you disconnect power from the switch, it resets and next
    time you give it power, it closes the circuit again. This component
    will work with 12 volts. Thanks in advance for any help.
     
  2. You can purchase time delay relays in many catalogs or from many mail order
    houses. The other solution is to make a capacitor charge up on application of
    power, switch on a transistor, and disable your relay (which would normally be
    on when powered up).
    So, the default condition when power is applied is "capacitor not charged,
    transistor conducting, relay on" and as time passes and the cap charges, the
    transistor is turned off. Or, you could go the digital route and build up a
    counter/timer circuit, but that is way too complex for such a simple task.

    Cheers!

    Chip Shults
    My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
     
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