Delivering a 10 second long, 12 volt DC signal

Discussion in 'The Projects Forum' started by tmetford, Apr 19, 2013.

  1. tmetford

    Thread Starter New Member

    Apr 19, 2013
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    At the moment I press to switch on, count to 10 and press again to switch off; hence delivering an approximately 10 second long 12 volt DC signal (~10mA current) to a relay on an old push-button telephone (I know it sounds like a weird thing to do on its own but it does have a useful function to do with diverting my telephone calls remotely and which I’m happy to explain but would take up too much space here).
    What I would like to be able to do is to press a switch to start the signal and then be able to leave it knowing that, after approx 10 seconds, it will turn itself off automatically so I don’t have to wait around for 10 seconds (I’m a type A personality it would seem)!
    What circuit/components would I need to achieve this please?
    Do ask for more information as needed and apologies if what I’ve explained thus far is as clear as mud!
    I have an elementary knowledge of DC electronics, basic circuit assembly skills and many errors to my credit. I’m really willing to learn the “how to” with the theory and practice but I don’t know where to start with this one!
    Many thanks in anticipation of your help
    Tim
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    This is a perfect application for a common 555 timer circuit. Look around on this site a bit for the 555 monostable multivibrator. What, you didn't know that was the magic term to look for? ;) Your manual switch will provide the trigger. You'll choose a resistor+capacitor to give the timing you want.

    The 555 will be able to handle the 10mA all by itself. Sometimes an external transistor is used to handle larger currents.
     
  3. #12

    Expert

    Nov 30, 2010
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  4. tmetford

    Thread Starter New Member

    Apr 19, 2013
    3
    0
    Big Thanks to Wayneh and #12 for your suggestions.
    Makes it all seem do-able even though the 555 timer will be a challenge!
    I'll see how far I can get before I need more help.
    Cheers
    Tim
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    Everything "new" has a learning curve, but the 555 is one you won't regret learning. It's the most popular IC ever, for a reason. It's very handy.
     
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