Sound Reactive LEDs

Discussion in 'The Projects Forum' started by Sizer, Nov 4, 2012.

  1. Sizer

    Thread Starter New Member

    Nov 4, 2012
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    Firstly Hi!...noob here....

    Im trying to do a project with my two lads and dont know a great deal about electronics. I know what we want to acheive, I think I know whats missing but dont have the knowledge to work out the particulars.

    Ive attached what we have worked out so far.

    We want:

    10 LED's to light up to music (all at the same time not a bar type thing).
    To be able to turn it off and on.
    To be able to turn off the light syncing leaving all LED's lit.
    To be able to adjust the Microphone Sensitivty.

    At the moment I believe the power from the Microphone needs to be amplified but I dont know how or how much to amplify it by. Id also like to know the workings out behind it I dont just want a solution, I want to learn.

    The transistor we are using is a TIP31c. (VCEO 100, IC 3, PTOT 40)
    http://www.maplin.co.uk/standard-bipolar-npn-power-transistors-33878

    The Mic :
    (0dB = 1V/µbar at 1kHz, Vcc = 4.5V, Rl = 1kΩ) 60dB ±3dB
    http://www.maplin.co.uk/omni-directional-sub-miniature-microphone-4565

    I would appreciate any help or nudges in the right direction.
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    761
    57
    Tune to a radio station at your home stereo. Listen normally any program.

    Turn volume to zero.

    Connect two leds in counterparallel to one channel of your home stereo amplifier speaker output, can be together with its speaker connected.

    Very slowly raise the volume, until leds flicker. Stop there. {One step at a time}

    Counterparallel means like these:
    http://t3.gstatic.com/images?q=tbn:ANd9GcSdSACs4Hm5rx4G2sKmrJeFrRbIOa5XFG59n0u225N0RtIGoOOk

    The features to turn all off; steady on, or flickering takes a 3 position switch; that will be explained later.
    The 10 leds instead of 2 will come after.
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Yes, the mic is a condensor mic and needs to be amplified and biased with a voltage.

    Check out this link:
    http://www.rason.org/Projects/hbmic/hbmic.htm

    Put a 100 ohm 1/4 resistor between R6 potentiometer wiper and the base of the transistor,
    I would power the mike with a 1.5-3volt battery through the R1 1K resistor, not from the circuit power because the mic is rated 4.5v max and it draws a small current.
    The preamp circuit could be powered from a 5vdc wall wort of 300ma capacity or higher
     
  4. Austin Clark

    Member

    Dec 28, 2011
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  5. Sizer

    Thread Starter New Member

    Nov 4, 2012
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    Thanks for the replies....i havent bought the mic yet so maybe i could get an alternative suitable for the 5v. Its only 5v as i planned to use usb to power it so it can be plugged into an xbox, pc or tv?

    Im still trying to get my head round the ideas suggested...
     
  6. bertus

    Administrator

    Apr 5, 2008
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  7. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Getting a higher voltage condensor mic is a good idea. I believe the 'normal' current limit of a usb port is 100 ma - your circuit will draw more than that - about 240 ma in sync off (always on) mode if the LEDs have a typical 2,1 v drop.
    You could increase the LED series resistors but of course this will drop the LED brightness.
     
  8. Sizer

    Thread Starter New Member

    Nov 4, 2012
    6
    0
    Ohh i thought it was 500, is there a way i can test it with a meter to check?

    Usb 2.0 is 150 mA so i just read somewhere..so may have to scratch that idea and got with a 12v adaptor
     
    Last edited: Nov 4, 2012
  9. Austin Clark

    Member

    Dec 28, 2011
    409
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    the higher the voltage is, the more energy you're going to waste as heat. You can buy 5V adapters.
     
  10. Sizer

    Thread Starter New Member

    Nov 4, 2012
    6
    0
  11. Sizer

    Thread Starter New Member

    Nov 4, 2012
    6
    0
    After some advice from other forums, Ive now updated the curcuit...what do you think?

    [​IMG]
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I corrected your circuit on the other website a few minutes ago.
     
    Sizer likes this.
  13. Sizer

    Thread Starter New Member

    Nov 4, 2012
    6
    0
    "The over-priced microphone is designed to be powered by 1.5V when it has a 1k series resistor. Then its voltage is half at 0.75V and its current is 0.75V/1k= 0.75mA.
    With my 9V supply then I use a resistor that is (9V/2)/0.75mA= 6k (use 6.2k) then it has a voltage less than 4.5V.

    Your new circuit has problems:
    1) Its opamp does not have a positive supply and does not have a ground.
    2) The 1k resistor that powers the mic wrongly powers the volume control and all the LEDs.
    3) The very low resistance of your volume control shorts the signal from the mic.
    4) It is missing an important supply bypass capacitor that prevents the opamp from oscillating.
    5) The transistor is an on-off switch that lights the LEDS when there is ANY sound so the LEDs will be almost continuously lighted when there is music instead of flashing with the beat.

    I fixed it:
    I use the transistor as a linear emitter-follower so the LEDs' brightness follows music or voice levels."


    Thank you for your help i will compare the two and your comments so i understand where i went wrong.

    1. The app doesnt let me add that bit...but yh i was aware it needed it.

    3. The VR was meant to adjust the sensitivity not the volume or is that what you meant?

    4. I read about them but perhaps misunderstood what it did, i thought it levelled out the voltage. So, i left it put so that the lights brightness varied depending on the level of the sound.
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I am an audio guy so when I see your "sensitivity" pot then I think it is a volume control.

    Your transistor is an on-off switch so it cannot adjust the brightness of the LEDs except to dim them with very narrow full power pulses (pulse-width-modulation).

    You need a supply bypass capacitor to "level out the voltage" because without it, when the LEDs turn on then the voltage drops which is amplified by the opamp until it turns off the LEDs then the voltage rises and it amplifies it then the LEDs turn on which causes the voltage to drop again .... over and over as a high frequency oscillation.
     
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