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.
Circuit Description
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 100
Ohm,
LEDs as per choice
Mark says
I have a 12 volt strip of under counter LEDs.I would like to hook up to my biombox to beat to music.I have a tip31 and tried to use that but no luck.can you help me with a circuit that will work.thank you
Swag says
use TIP122, connect base with music signal through a 1uF/25V capacitor and with a 1K series resistor, connect the LED strip across positive 12V and collector of the transistor, connect emitter with the negative of the supply and also the music negative line.
Kesava Raj says
Thank u sir…*
Kesava Raj says
Few doubts sir…
* In diagram preset value 1k mentioned..
1k or 10k
* For using high power amplifier like stk4141 and mosfet ic…speaker output power will be high , so this circuit itself enough or we want to change transistor and capacitor value…
* There is many pnp transistor but y u choosing 557 only ..pls tell the reason or any other transistor we can use ?
Swagatam says
Keasva here are the answers…
1) it's 10K preset
2) for high power input just add a 100 ohm resistor in series with the PNP transistor base capacitor
3) the voltage and current requirement for this application is within the BC557/BC547 range, nonetheless the similar BJTs can also be sued.
Sharon Er says
Hi engineer, if I don't want to connect speaker, can I use voltage? I want to construct this circuit in multisim and do simulation, but I don't what can I put for the speaker component.
Swagatam says
Hi Sharon, sorry I did not understand your question, how can you replace the speaker with a voltage??
Sneakcode world says
hello engr..please how can i get the circuit, i cant find the circuiut
Swagatam says
please build the circuit
brod says
Can i replace the diodes by 1N4007
Swagatam says
yes…will do
Jenson Costales says
Sir Swagatam, Can I use a tip42 at the input section instead a small power general purpose pnp?
Swagatam says
sorry tip142 will not give proper results
Jenson Costales says
Sir Swagatam, Can I add this circuit from 5 LED's,transistors and diode's Into 10..
Swagatam says
Hi Jenson, yes you can do it.
For more efficient results you can try the IC LM3915 circuit as given here:
https://homemade-circuits.com/2012/03/how-to-make-simple-vu-meter-circuit-at.html
Anonymous says
sir i tried this circuit but it is only blinking ?
Swagatam says
what is happening with your circuit??
ivan dela cruz says
follow up question, can you show me the diode that you used. .
Swagatam says
it's 1N4148, you can check out its datasheet for the spces….
ivan dela cruz says
quick question, does it work like an equalizer?
Swagatam says
No..
ivan dela cruz says
so this circuit is like a blinker?do you have a circuit for equalizer using transistor?
Swagatam says
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.
ivan dela cruz says
sorry, i mean for the equalizer is like an spectrum analyzer using transistor only. is it possible sir?
Swagatam says
you will have to make many such circuits and arrange each LED channel like bars…..
ivan dela cruz says
can you make a circuit of that sir?without using an IC?
Swagatam says
I'll try it out sometime later and post it.
ivan dela cruz says
thank you sir, i am badly needed it.
Anonymous says
is it lit altogether? or by peak?
Swagatam says
by peak.
Anonymous says
sir,, what is the use of the capacitor in the circuit? can i remove it?
Swagatam says
it's for isolating the transistor from DC potentials….
efdat says
thanks, it works very well
Anonymous says
Did u try this practically? Pls let me know…..
Swagatam says
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.