3 second bell ringer circuit

Discussion in 'The Projects Forum' started by Pillarman1009, Apr 28, 2012.

  1. Pillarman1009

    Thread Starter New Member

    Apr 28, 2012
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    I am new to here so bear with me.

    I have a project for my employer involving a bell (12V dc) and a momentary switch to activate it. I need a circuit that when the switch is activated for even a split second will ring the bell for 1.5-3 seconds the shut off until the switch is pressed again. The supply power will be 120v ac. Again, the bell will need to start ringing off of the slightest connection from the switch. Any ideas will be appreciated. I'm not very circuit savy so please include the circuit to switch to dc 12v
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    A 555 one-shot circuit will provide the timing that you want, and can be used to control a relay or a MOSFET to switch the 12 VDC to the bell. What is the current required by the bell?
     
  3. Pillarman1009

    Thread Starter New Member

    Apr 28, 2012
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    It is 0.125 amps.
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    That's not very much current, so the power supply should be easy. Your best bet for power would probably be a 12 VDC "wall wart." You would need to find one with a current capability somewhat higher than .125 amps (which is the same as 125 milliamps) ; 200 mA or larger would do.

    A regulated unit would be best, but they are not terribly common. You might have to use an unregulated supply and a separate regulator circuit, but that's not difficult.

    What are your electronics knowledge and skill levels, i.e., schematic reading, assembly, soldering, etc.?
     
  5. #12

    Expert

    Nov 30, 2010
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    The monostable circuit is in a book at the top of this page. Vol VI-Experiments, Chapter 8

    Lucky you, an NE555 can conduct 200 ma so it won't need an external power transistor.

    Is your "bell" mechanical or electronic? The mechanical bells are not all that picky about having a nice, clean, regulated power supply at exactly 12.0 volts.
     
  6. Pillarman1009

    Thread Starter New Member

    Apr 28, 2012
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    #12

    It is a mechanical bell, but i need it to be solid sounding and loud. So no large variations in voltage.

    Tracecom

    I am a very quick learner and have decent experience with schematics as well as soldering and other electronics related topics.

    To give you more detail, we want to use a limit switch for the trip switch. A log climber will bump it with a safety rope when he reaches the top. It will trigger a 3 second chime loud enough to be heard by an audience 30 feet below and spread out over a 50 yard radius. After 3 seconds it will self silence and be ready for the next climb.


    ----------------------------------------------

    #12

    Thanks for the monostable multivibrator circuit. I'm going to try it. Ill post results.
     
    Last edited: Apr 29, 2012
  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    Since your bell is electromechanical a back emf diode must be used or you will pop the 555.
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    So this is an electromechanical bell. Does it strike only once when the power is applied like a gong, or is it a repetitive striking as long as power is applied like a fire alarm bell?

    Ken
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    You can can increase or decrease the ring time by changing the values of either R2 or C1.
     
    #12 likes this.
  10. #12

    Expert

    Nov 30, 2010
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    To avoid large variations in voltage, use a large enough power supply, as tracecom recommended.

    My point is that a mechanical ringer doesn't need an excellent regulator. A common wall wart should be good enough, even if it isn't "regulated".

    PS, excellent schematic, CDRIVE.
     
    Last edited: Apr 29, 2012
  11. Pillarman1009

    Thread Starter New Member

    Apr 28, 2012
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    The bell will hit repeatedly until power is cut at the end of the timer.

    Can somebody post a modified version of the mono stable circuit quoted above with the protection for the 555 inserted?
     
  12. #12

    Expert

    Nov 30, 2010
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    It's in post #9
     
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