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!HELP! - Tip31 LED strip project

Discussion in 'General Electronics Chat' started by unbeatable97, Aug 4, 2013.

  1. unbeatable97

    unbeatable97 New Member

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    I have started a project using a tip31 transistor, 12v power supply and 5m of blue leds. I would like to extend this project but i can't figure out how to either boost the audio signal, or to find a bigger transistor.


    I am using:
    12v 20a power supply (yes i i know that is a huge amount of power just for leds)
    12v 2a leds
    tip31c transistor
    7.5a marine grade power cord.

    I am new to all this so if you could keep it fairly straight forward, it would be greatly appreciated.
    I will provide pictures or diagrams if needed.

    Thanks, Nick
     
  2. dr pepper

    dr pepper Well-Known Member

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    You need to find a schematic for a audio to pwm (pulse width mudulation) circuit, that is if you want the led string's brightness to be modulated by music.
     
  3. unbeatable97

    unbeatable97 New Member

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    I have it all set up and working, its just if i add in another circuit for another 5 metre roll, the audio signal won't be loud enough, and i can't run anymore leds off of the existing transistor as it only has 1 amp free and the rolls are 2 amps. I am aiming to have led's all over my room.

    Thanks
     
  4. dave

    Dave New Member

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  5. dr pepper

    dr pepper Well-Known Member

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    It might be possible to add another trans to deal with the extra led strings, or maybe replace the one you have with something that has more capacity.
    We need to know more about what you have, do you have a schematic?
     
  6. unbeatable97

    unbeatable97 New Member

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    FMZXXB8G5W7R47J.LARGE.gif
    This is the exact schematic i used. I obviously swapped out the 4 individual leds and added a 5m string and i am using a 20 amp 12 volt power supply i bought off ebay. i have read about overloading your Led's but at the moment, the volume isn't loud enough to do so. i would like to upgrade the transistor but i don't know which one i need

    Thanks
     
  7. dr pepper

    dr pepper Well-Known Member

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    Thats so simple, I wouldnt have thought that'd work that well, but if your happy with it.

    What I'd do there is add another transistor to power your other string of the same power pack, just put the other transistor an the opposite channel, so you'd get a stereo vu.

    The problem is with a 'biger' transistor is that the gain will probably be lower which means it'd take more to drive it, which might be beyond the capabilities of a headphone socket.

    If you want to power a load of strings then you'd probably need a circuit that generates audio modulated pwm and then use a mosfet, probably wouldnt need a heatsink, your circuit most definately will.
     
  8. alec_t

    alec_t Well-Known Member Most Helpful Member

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    What is the source of the audio signal? An 'Aux' output? The loudspeaker terminals of an amp? .......?
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The extremely simple circuit is an Instructable and was "designed" by a 10 years old kid who knows NOTHING about electronics.
    It is missing important parts:
    1) A series base resistor to limit the transistor base current to prevent the audio power amplifier and TIP31 transistor from blowing up.
    2) A diode from base to emitter to prevent the reverse-bias emitter-base voltage from exceeding its maximum allowed voltage of only 5V.
    3) A current-limiting resistor in series with the LEDs to prevent them from blowing up.

    You do not need PWM. The transistor rectifies the audio and lights the LEDs on the loudest parts of the music.
     
  10. unbeatable97

    unbeatable97 New Member

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    Sorry for the late reply, i have been a bit busy lately.

    The audio source i am using is a headphone jack from my laptop of portable device.

    If it wasn't too much to ask, could someone design a wiring diagram for me? I have looked around and they all look too complicated.

    Thanks in advanced.
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Since you bought no-name-brand LED strips from E-Bay then the details of their maximum allowed current and if they already have a current-limiting resistor are unknown.

    Connect a 33 ohm resistor in series with the base pin of the transistor. Then when the music level reaches 0.6V the LEDs will begin to light. If the music level can go as high as 1.4V then the base current is 21mA and the LED current is at least 950mA if there is no current-limiting resistor.
    The LEDs might not appear bright because they are turned on only half the time (the transistor is a rectifier) and are turned on for very short durations that your vision can barely see.

    A more complicated circuit works much better.
     
  12. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Adding a second LED string would require a second TIP31 and hence double the current drawn from the headphone jack. Can the jack provide ~ 40mA? As AG says, a more complicated circuit would work better.
     

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