What is the Theory of police lights BJT Emergency LightsCircuit?

Discussion in 'The Projects Forum' started by ElfBoy, Mar 15, 2012.

  1. ElfBoy

    Thread Starter New Member

    Mar 15, 2012
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    hi guys.... i just want to ask if you know the theory of police lights, this circuit build using a breadboard, but i don't know how if flows and i have to make a theory about this circuit can you help me plsssss....

    This circuit flashes the left LEDs 3 times then the right LEDs 3 times, then repeats.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    How this is made. Is by using logic circuits, or a micro-controller. We are not allowed to discuss automotive modifications in this forum. But I think it should be OK. If we restrict us to discuss this on a model level only blinking a few LEDs. Like you would have done in a say model car.
     
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  3. BSomer

    Member

    Dec 28, 2011
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    Most commercially available "police lights" are using microcontrollers. It can be done without micros though, something as simple as a 555 and CD4017 comes to mind.
     
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
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    A small breadboard version of an alternating triple flash circuit can be built using a 555 timer, 4017 counter, some OR gates or diodes, two transistors and passive components.

    If what you need is a description of the theory of operation for a particular circuit, you would need to show the circuit schematic in order to get specific help.
     
    Last edited: Oct 29, 2012
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  5. ElfBoy

    Thread Starter New Member

    Mar 15, 2012
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    [​IMG]

    this is the circuit that i been asking, i want to know the flow of this circuits.
     
  6. BSomer

    Member

    Dec 28, 2011
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    Yup, that is kind of what I was thinking of. Basically the 555 timer is set up as an astable multivibrator. It generates high and low clock pulses that are fed to the CD4017.

    The 4017 is a decade counter, each clock from the 555 triggers the 4017 to turn on an output. I cannot recall if it is triggered on a rising or falling edge though. Output 0 is turned on at the first clock signal until the next clock signal is received at which time it shuts off and output 1 is turned on. The 4017 wil continue through this cycle 0->1->2->3->etc.. to the last output then back to output 0.

    The outputs that are tied to the transistors turn them on which allow current to pass through the LEDs. As you can see in the diagram every other output of the 4017 is tied to the transistors. This allows a pause in the flash pattern. The diodes on the outputs prevent current from going back into the 4017 when one of the other outputs tied to the same transistor is on.

    This is just a summary of the operation of that circuit. If you would like more details, read up on Bill_Marsden's blog on the 555 and associated flasher circuits. He has done a really great job with his entries there. http://forum.allaboutcircuits.com/blog.php?b=378

    I hope this helps you out a little.

    --Brian
     
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  7. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Is this for a school assignment or merit badge requirement or something other than personal interest?
     
  8. ElfBoy

    Thread Starter New Member

    Mar 15, 2012
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    Its for my documentation.
     
  9. ElfBoy

    Thread Starter New Member

    Mar 15, 2012
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    Thank you.. ^_^.
     
  10. ElfBoy

    Thread Starter New Member

    Mar 15, 2012
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    Now my only need is block diagram, but i really dont know how to make a block diagram,... do you know how to make a block diagram for this?
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If you look at the ckt, it is already almost a block diagram- just leave out all extrarous wiring, so you have Clock- Counter- Logic- Drivers-LEDs
     
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  12. ishaan3731

    Member

    Jun 23, 2011
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    Ur circuit dosnt need much modification to create a block diagram out of it.......... remove resistors from the circuit , instead of showing four diffrent leds .....try make a led bar of four leds in shape of a block...... replace transistors,diodes,ic 555 and cd4017 by blocks of varying sizes.....the block diagram wont reflect inner details but it should have the capability of explaining the concpet involved!!!!

    Best Of luck!!!!!
     
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  13. ElfBoy

    Thread Starter New Member

    Mar 15, 2012
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    thank you!
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    Think OR gates. I have made an improved version of that circuit myself, complete with PCB, but I can't post it here.

    While the logic family is not obvious, it is there.
     
  15. gunasekhar

    New Member

    Oct 11, 2012
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    iwant the theory on how the "police car lights with leds using 555timer and cd4017"works...just theory please..
     
  16. Wendy

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  17. Audioguru

    New Member

    Dec 20, 2007
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    The 555 oscillator is the first block.
    The 4017 sequencer is the second block.
    The diodes and transistor drivers are the third block.
    The LEDs might be a fourth block.
    A battery that powers it might be a fifth block.
     
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