# Guide me for successfully making a single LED react to sound frequency

Discussion in 'The Projects Forum' started by vadimqew, Apr 16, 2011.

1. ### vadimqew Thread Starter New Member

Apr 9, 2011
4
0
Hello there again,

This is my second thread so far for the same project. I have tried to make a very simple color organ. I have tried to make more complicated with 3 LED but no success. I need some guidance from you.

What I'm trying to do is have an LED react to a certain input frequency from a sound source like 3.5mm jack. I'm doing this for a school project and the more I research, the more complicating it gets for me. The time is running out for me so I'm forced to do just a simple one.

I would preferably make the circuit out of the parts I have already.

Materials:
op-amp LM358N (can be powered by a single source as low as 3V)
Transistor - NPN TIP120 (too powerful? 65w)
can get any close value resistors and some LED
2 9Volt batteries
3.5 mm jack
and only .1 micro Farad Capacitors

So far i have tried following this circuit

the guy that made the circuit said to use the formula below to find the unknown values.
I have used his formula (frequency=1/(2*pi*R*C), and I'm assuming the just for that filter R3=R4=R8=R11 so My R was 13.26K at 120Hz with the use of .1 microFarad capacitor

Here is the circuit I want to build, but not all the values are known to me and if it should work. It is a inverting single power supply connection. I was wondering if the right Rf and Ri values are found, could it be used as a filter to filter around 2Khz as an example for mids. Circuit is shown below. I would appreciate any help and if anyone could guide me into finding the right values for either the first full circuit or the one i drew myself. Someone before suggested looking at their chapter 12 they wrote, but the circuits are too complicated for me to understand, I'm just getting into this so the basic, the better.

thank you
have a wonderful day

Apr 9, 2011
4
0

Apr 20, 2004
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4. ### qlue New Member

Apr 15, 2011
5
0
I don't want to discourage you, but you're trying to run before you can crawl.
The second circuit, the one you drew yourself, doesn't make much sense to me.
However, in the first circuit, R7 to R9 will be the same value, probably 470K should work. Resistors R1 to R6 will all be the same value and will depend on how much gain you need. (try 47k, that will give you 10x gain which should be good enough for a standard audio socket as source)