help with touch-on/touch-off relay switch

Discussion in 'The Projects Forum' started by sideburn, Oct 2, 2009.

  1. sideburn

    Thread Starter New Member

    Oct 2, 2009
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    hey guys. im trying to make a project that will switch a relay on when you send low signal and turn the relay off if you send the signal again after a it does not receive a signal for 10 seconds or so.

    in otherwords i want to be able to trigger a transistor that kicks on a relay but if i keep triggering over and over the relay stays on, but if i wait 10 seconds or more and retrigger then the relay shuts off and stays off unless i wait 10 seconds again.

    i want the signal to be able to be very low like the speaker output from an alarm clock.

    thats a third example.. if i hook the curcuit to an alarm clocks speaker output.. then the alarm can go beep, beep, beep, beep... the first beep kicks onthe relay.. the relay stays on even after i hit snooze to stop the beeps.... then after 10 minutes the alarm ends the snooze period and goes beep beep beeep.. and the first beep shuts the relay off, and it stays off.. until the delay and the process repeats.

    sorry for the long winded explanation..

    my guess is i need a 555 timer, some npn transistors, maybe a capacitor or two, and a relay.

    can someone help me draw up a schematic for this?

    i hope so! Thanks for reading,


    -Tavis
     
    Last edited: Oct 2, 2009
  2. flat5

    Active Member

    Nov 13, 2008
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  3. sideburn

    Thread Starter New Member

    Oct 2, 2009
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    thanks.
    so is the a push on push off circuit though?
    doesnt look like it


    i need it to be a push on.. stay on unless the button has not been pushed within a certain delay.. then push off..
     
  4. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Yes, you're right about the off function.
    What is needed is a gate to detect if the trigger (pin 2) is low and the output (pin 3) is high.
    If so, send a pulse to the reset (pin 4).
    A small delay will be necessary from the output to the gate or the reset will always happen.
    This may do what you want.
    You need to change the reset circuit (pin 4).
    Add it to the circuits above.
    Two resistors, an npn transistor (2n2222) and a capacitor will be required.
    The parts you add are R1, R3, C1, Q1.
    I don't know what value to select for the capacitor. You might need an electrolytic.
    Start with 0.1 uf.

    I hope there are comments from engineers telling me if this will work. Note: read update in post #7

    Darn! I don't see the icons to allow me to post an attachment, so...
    http://flat5.simpload.com/?f=555reset2.gif
     
    Last edited: Oct 5, 2009
  5. sideburn

    Thread Starter New Member

    Oct 2, 2009
    4
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    thanks.
    i will study this up
     
  6. flat5

    Active Member

    Nov 13, 2008
    403
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    The parts you add are R1, R3, C1, Q1.
    If you need an electrolytic capacitor, the negative side goes to the switch/ground. I guess you know that.

    I'd like to know if you use this and if it does what you want :)
     
  7. flat5

    Active Member

    Nov 13, 2008
    403
    17
    "in other words i want to be able to trigger a transistor that kicks on a relay but if i keep triggering over and over the relay stays on, but if i wait 10 seconds or more and retrigger then the relay shuts off and stays off unless i wait 10 seconds again."

    Re-reading your first post I see my addition won't do what you want. I think using two 555 ICs (556) you can do it.
    What I'm thinking is to build what is discussed above but trigger it by another timer set to ten seconds. (move the switch)
    The switch turns the output of the first timer (T1) high and it will ignore any more input on it's trigger until it times out (ten sec). T1 triggers T2 (our org. timer circuit but with an inverter and cap/pullup between it and the second timer's trigger input) which has a very long on time (ten minutes?). If T1 is triggered again after ten seconds it will again trigger T2 which will reset.
     
    Last edited: Oct 14, 2009
  8. sideburn

    Thread Starter New Member

    Oct 2, 2009
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    i had to get back to $$ work for a bit so i havent got back on this yet.
    I was thinking maybe using a microcontroller chip instead.
     
  9. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Thanks for keeping us informed.
    I have never played with microcontrollers.
    That seems very complicated to me :)
    For this simple function, I think a few gates or the two 555 monostables will do nicely.
     
  10. Chris15

    Active Member

    Apr 15, 2009
    252
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    Do you know if you could use the same principle except trigger the relay on latch with some NPN's then unlatch with the same power source

    E.g, 2 wires with 3v at the power of a wireless switch, button pressed relay latches, button pressed again, relay unlatches

    If you can help please

    Chris
     
  11. flat5

    Active Member

    Nov 13, 2008
    403
    17
    I don't really understand what you are asking.
    To latch and then unlatch a relay with a momentary switch you can use a "flip-flop".

    Wireless?
     
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