LED flashing syncronized on music (need help)

[shevchenco]

Hi!
I want to make a circuit that makes LED to flash depending by sound. I have read some documentation and I made a sample of circuit, but the implementation does not work as I want View attachment IMG.jpg. I attached the schematic and if someone find what am I doing wrong please tell me (any schematic that is working will be welcome too ).
Thanks!

 

[D.A.(Tony)Stewart]

THe OA has no feedback to limit gain and no current spec to drive low R.

What response do you expect? There is limted proportional brightness or slow decay. The series caps will act as +ve clamps to Vbe also.

Primitive design gives primitive results. Bypass the Op Amp.

Start with specs on what response you need for input range, f band, attack, decay.

You end up compromising , dynamic range, poor peak detection with the positive clamp effect from Vbe and have no hold time.

A far better design uses quad OA's to isolate filtering, Peak detect, log compression, attack decay control. , voltage to current. The advantage is smaller value caps for signal processing then drive with voltage control current sinks.

The input impedance of each circuit compromises the result with the source impedance non-zero causing interaction and you end up needing several Vpp to drive the mid band,

Do it right. Start Over.

 

[Audioguru]

Here is a circuit that uses a quad opamp )almost any quad opamp can be used) for the filters and rectifies the signals before transistors drive the LEDs.
Notice that the LEDs are in series, not in parallel. LEDs each have a slightly different voltage, unlike light bulbs. Then when in parallel the LED with the lowest voltage hogs most of the current and is very bright and might burn out soon while the other LEDs are dim until it is their turn to suddenly go bright and burn out.

 

[Externet]

Perhaps this will please you :
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[chuckey]

I think that you have to sort out the LEDs. If they are typical .2" low current jobs, then they will need about 2 V at 20 mA. So if you drive ONE LED from each transistor, you have 5V supply, less .2 across the transistor and 2V across the LED, this gives you 5- 2.2 = 2.8 V to loose. So you put a 2.8/.02 ohm resistor in this circuit = 140 ohms (150 should do). So if you want more then one LED, you use more, a 150 ohms in series with each LED.
Now any transistor needs 60 mA collector current so you should allow 60mA/100 = .6 mA base current.
With your opamp running like it is the output will be a succession of square waves, with very little in between 0 and 5V, so you must reduce its gain ( or the input level) so only the very loudest peaks actually hit +5V.
Now feed the output of the opamp to the three bases via two 4k7 resistors in series. If you try the circuit out it should work but all the LEDs should flash at the same time.
Try connecting a 4.7 MF cap between one 4k7 junction to earth (+ to resistors, - to earth). This should remove most of the treble/middle frequencies and one LED should pulse to the base. Adjust the value of the capacitor to taste.
Try connecting a .5 MF across both the 4K7s, this then should make one LED pulse to the treble. Adjust cap to taste.
Try connecting a 2 MF cap from the centre of the 4K7s to earth and a 1 mF across the resistors, if you are lucky this LED will pulse to the middle frequencies.
As said this is a crude circuit. It really needs better filters and a pulse extender and a circuit to equalise the light output with the music level.
Frank