Rear Bicycle Brake Light

Discussion in 'General Electronics Chat' started by crepa, Jun 17, 2012.

  1. crepa

    Thread Starter New Member

    Jun 17, 2012
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    Hello, I'm relatively new to electronics so I apologize if my questions are a little bit basic.

    Now to the project. I have a break light for my bike with 4 LEDs (see picture). First I would like some help to draw the circuit diagram based on the printed circuit board and the picture to identify the components. I've numbered some elements that I've identified in the picture:
    1)switch that goes to the bicycle brake
    2)BC547B - NPN transistor
    3)22 microF capacitor
    4)22 Kohm resistor
    5)27 ohm resistor
    6)1N4148 diode

    Numbering the LEDs from left to the right 1 2 3 4, one can see that LEDs 1 and 2 are blinking alternately and so are LEDs 3 and 4 when all the LEDs are on. When I brake (or push the switch) they all start to blink together.

    So what I would like to do is to modify the circuit to have all LEDs on at the same time and when I brake they brighten up a little just like a automobile break light.

    Thank you in advance,
    Gabriel
     
  2. stoopkid

    Member

    Mar 3, 2011
    136
    1
    You would probably want to use a 555 timer to do this. This circuitboard would probably be pretty much useless. It would be less of a modification and more of a total rebuild.

    Then again you may be able to coax it into doing what you want, but someone more experienced would have to figure that out. I guess if you made them alternate fast enough that would be like a 50%PWM, then the brake switch could just power them all at once.
     
  3. #12

    Expert

    Nov 30, 2010
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    Here's an idea.
    Edit: You could just short out R2 with the brake switch instead of using a transistor.
    Sorry. Had a brain failure while I was drawing.
     
  4. crepa

    Thread Starter New Member

    Jun 17, 2012
    5
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    The drawing is very good thank you. However, I'm not sure if I understand it. You are saying that I should remove one of the transistors and replace it with the brake switch? What this mod would do to the LEDs in terms of illumination? Can you explain with more details please? Because it is my first project and I'm a little lost.. Sorry
    Thanks
     
  5. #12

    Expert

    Nov 30, 2010
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    I'm not telling you what you should do. I'm showing you a circuit that will do this:
    If you can't understand it, I certainly wouldn't say you should use it.

    Description: a full wave rectifier just to make sure whatever electricity is available gets fed in at the right polarity. That is followed by a pair of 2 LED series strings with current limiting resistors in 2 stages. Then there is a transistorized adapter that will respond to a switch that grounds pin 3, assuming that point "C" is used as common.
     
    Last edited: Jun 18, 2012
  6. crepa

    Thread Starter New Member

    Jun 17, 2012
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    It's not that I don't understand anything that you did.. Its just that I'm not used to using transistors or transistorized adapters.
    Well thank you for your help.
     
  7. #12

    Expert

    Nov 30, 2010
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    ..........
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    What's your power supply, type and number of batteries? Does the unit have a power switch or just the brake switch?

    The good news is that a bi-level, non-blinking light doesn't take much circuitry. The bad news is that you may as well make it on a new board.
     
  9. crepa

    Thread Starter New Member

    Jun 17, 2012
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    The circuit uses two AA batteries and it does have a power switch and the brake switch. But it only work on the modes I described before, I mean once its on the blinking pattern will change only if I "hit the brakes".

    I don't see a problem on making a new board to replace the other one.
     
  10. KJ6EAD

    Senior Member

    Apr 30, 2011
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    This is the simplest way to do it using your batteries and switches. The 4 LEDs and 5 resistors would be mounted on a replacement PCB. The resistor values were selected to provide approximately 10mA to each LED in tail light mode and 20mA to each in brake mode with a 3V supply. The resistor values may need to be adjusted to accomodate the Vf of your LEDs. The ones I used for design had a Vf of 1.7 at 20mA.

    [​IMG]
     
    crepa and #12 like this.
  11. #12

    Expert

    Nov 30, 2010
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    It gets easier when we know the voltage that is available!
     
  12. crepa

    Thread Starter New Member

    Jun 17, 2012
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    Thank you very much. This was the type of circuit I was looking for, very robust and efficient yet simple.
    I will try to build it as soon as possible.
     
  13. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
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    You're welcome. I would have posted it much sooner but the AAC attachment manager doesn't play well with Android. I had to use a third party image host.
     
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