Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.

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Monday, December 19, 2011

LED Music Level Indicator Circuit Diagram

The shown LEDs in the circuit sequentially light and "dance" as per the level of the music applied at the input, preferable directly from the speaker terminals of the audio gadget whose music level is to be monitored.
The proposed LED music level indicator circuit may be understood as follows:

The components which support the LED illumination are the associated NPN transistor, the emitter resistor, the base preset and the corresponding diode.
The above stage is identical to all the LEDs included in the circuit for obtaining the desired push-pull effect in response to the applied music level at the input.
However there's one difference between the LED stages, though most of the component placement is similar, the diodes form a different pattern.
If you see the circuit closely you will find that the the ground to the first transistor/LED stage from left comes across only a single diode, however the preceding stages ground potential has to encounter the extra corresponding number of diodes in theor path.

As we all know that a diode has the property of dropping 0.6 volts, means that the first transistor would conduct much sooner than the second, the second transistor conducts sooner than the third and so on.
Because as the number of diodes increase in the path of the respective transistor, the conduction is inhibited until the the voltage sufficiently increases for bypassing the diodes overall forward voltage.
This increase in voltage can happen only when the pitch of the music increases, giving rise to a sequentially running LED bar graph which shoots forward in response to the pitch or loudness o the applied input music.

The transistor at the input is a PNP and complements the rest of the transistors employed for illuminating the LEDs. The PNP transistor at the input amplifies the applied low level music sinal to levels which is just enough for illuminating the LEDs with reference to the music levels,.

Parts List for the explained LED music level indicator circuit

All NPN Transistors are BC547,
PNP Transistor is BC557,
All Presets are 10K,
All resistors are 100Ohm,
LEDs as per choice

                                                                                          

24 comments:

  1. Replies
    1. Did u try this practically? Pls let me know.....

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    2. Yes i tried it long ago and it worked, I think you too have made it successfully, you said it in the previous comment above.

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  2. sir,, what is the use of the capacitor in the circuit? can i remove it?

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    Replies
    1. it's for isolating the transistor from DC potentials....

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  3. is it lit altogether? or by peak?

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  4. quick question, does it work like an equalizer?

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    Replies
    1. so this circuit is like a blinker?do you have a circuit for equalizer using transistor?

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    2. i didn't understand when you said "equalizer" type....it's not a blinker type it's a sequential type, and will move to and fro with music peaks.

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    3. sorry, i mean for the equalizer is like an spectrum analyzer using transistor only. is it possible sir?

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    4. you will have to make many such circuits and arrange each LED channel like bars.....

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    5. can you make a circuit of that sir?without using an IC?

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    6. I'll try it out sometime later and post it.

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    7. thank you sir, i am badly needed it.

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  5. follow up question, can you show me the diode that you used. .

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    Replies
    1. it's 1N4148, you can check out its datasheet for the spces....

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  6. sir i tried this circuit but it is only blinking ?

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  7. Sir Swagatam, Can I add this circuit from 5 LED's,transistors and diode's Into 10..

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    Replies
    1. Hi Jenson, yes you can do it.

      For more efficient results you can try the IC LM3915 circuit as given here:

      http://homemadecircuitsandschematics.blogspot.in/2012/03/how-to-make-simple-vu-meter-circuit-at.html

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  8. Sir Swagatam, Can I use a tip42 at the input section instead a small power general purpose pnp?

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