I need help with a trigger and timmer

Discussion in 'The Projects Forum' started by larry gardner, Nov 17, 2013.

  1. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    I want to build a metal target for airguns. It will be a metal plate with a 1" center hole drilled it. There will be a metal plate behind the first plate that must be hit buy shooting through the 1" hole.

    I want to put a limit switch on the bullseye. I would like to have a circuit connected to the limit switch to turn on a flashing Led ( I already have the flashing LED) for several seconds

    I need a circuit that when activated will power the led for a few seconds maybe around 4 seconds give or take. I need this to run on 12v

    I am a amature machinist so metal work is no problem. I need help with the circuit. I would like to build several of these targets for my step daughter. I think it would help keep here interested.
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Sounds like you need a simple NE555N monostable multivibrator, otherwise known as a one-shot. Do you have the knowledge and tools to build it if you can get a schematic? If so, this should work. When the switch is depressed, pin 3 of the 555 will go high and stay high for 10 seconds. If your flashing LED is connected through a current limiting resistor of 1k, it will flash for that ten seconds.
     
    Last edited: Nov 17, 2013
  3. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    This would honestly be my first circuit. I can solider and I think I understand enough to build a simple circuit with good instructions. If you could supply a schematic and the list of components I need to buy I would really appreciate it
     
  4. tracecom

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    Apr 16, 2010
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    Have a look at the schematic on post #2. Does it make sense?
     
  5. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    I do not fully understand it but I have a friend that can help. Can you provide me with a list of components to buy. I can research and learn what I need to know to build it.
    Thanks
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    You will need:
    1 NE555N IC
    1 8 pin socket for the IC (optional, but recommended)
    2 .1 uF 50V ceramic capacitors
    1 .01 uF 50V ceramic capacitor
    2 10k ohm 1/4 watt resistors
    1 910k ohm 1/4 watt resistor
    1 10 uF 35V electrolytic capacitor
    1 1k ohm 1/4 watt resistor
    1 flashing LED
    1 momentary normally open switch suitable for mounting on the target
    something to build the circuit on (perfboard or stripboard or something else)
    some 24 or 26 awg hookup wire
    rosin core solder and small soldering iron
    tools
     
  7. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Get a cheap breadboard from Radio Shack. Build it on breadboard first, don't solder anything until you have working prototype on the breadboard.
     
  8. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    If I want to power the led for less time what current limiting resistor value can I experiment with?
     
  9. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    I got interested in learning about circuits several years ago and bought a bread board and quite a bit of components. I just never got around to doing the project that I bought them for. Thanks for the suggestions
     
  10. tracecom

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    Apr 16, 2010
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    The on time is controlled by R1 and C1. Make C1 smaller and the time is shorter; the change is proportional. Or you can change R1; make R1 larger and the time is shorter. If you know what time you want, I'll tell you what R1 and C1 values to use. The formula is 1.1 X R (in ohms) X C (in farads).
     
  11. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    To change time you need to change R1 resistor and C1 capacitor in this schematic:
    http://forum.allaboutcircuits.com/attachment.php?attachmentid=61600&d=1384739100

    I looked at Bill_Marsden blog.
    http://forum.allaboutcircuits.com/showthread.php?t=14018
    The formula:
    Time=1.1*R1*C1

    In the example above:
    Time=1.1*910000*0.000010=10.01 seconds

    So, if you want different time, plug time into equations above. I think keep capacitor the same, they are kinda limited. Calculate new resistor that you will need.

    If the resistor value is too odd. There are two ways to get close to the value you need.
     
  12. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    I think if can figure out the time. Where do you recommend I buy the components?
     
  13. shteii01

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    Feb 19, 2010
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    Well, you said you wanted time of 4 seconds, so
    4=1.1*R*0.000010
    R=363636.36 so figure 363.6 kOhm
    360 kOhm is one of the standard resistor values, so use that to begin with.

    Most of your parts will likely come from Radio Shack.

    Digi-Key, Mouser are the other usual places in US to order stuff from.
     
    Last edited: Nov 17, 2013
  14. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    I placed a order tonight. I got caught up trying to get everything and did not change the resistor value. Cant wait to make a working circuit for the first time!

    Thanks for the help
     
  15. tracecom

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    Apr 16, 2010
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    If you ordered any extra 910k resistors, you can put two of them in parallel, and the time will be cut in half to 5 seconds.
     
  16. larry gardner

    Thread Starter Member

    Sep 17, 2008
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    I bought some 220k off ebay. That should give close to 2.5 seconds of flashing LED. I will play with it on the bread board and when I have it right put it on a board and install it. I could not have started this without your help.
     
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