Sound to Light Converter

[Tan9890]

hi..
I'm using this circuit in my project. Its a sound to light converter..
the output voltage varies according to the sound intensity on the mic..

Now, I'm going to use this output voltage as an input to Atmega32 ADC.. Afetr that, based on the voltage levels, i'l drive a dc motor..

here is the circuit diagram

**broken link removed**

So, I have a few questions, kindly answer them, please..


1. Can anyone explain me full the operation of the circuit?

2. At the output, i.e. the base on the transistor, there is negative voltage..
Can Atmega 32 accept negative voltage for ADC conversion? If not, how can i convert it to positive, i.e of the same value..

3. I need to make the mic 'directional', Is there any way to do so?
kindly help me out... I'm using this for my project.. so i need some info.

Thank You.

 

[Reloadron]

The circuit uses a LM358 dual operational amplifier with a single supply voltage from a 9 volt battery. It is a single supply and referenced to 0 volts or ground there is no negative voltage anywhere. There can't be a negative voltage. I think you need to read and understand the data sheet for the LM358 and what a single supply actually means.

The circuit also uses an electret microphone. That type of microphone is noted for being omnidirectional. I suggest you read this and understand a little about that microphone as well as finding data on directional microphones more suited for your application. An electret is not the best choice if you want a directional microphone unless you do some modifications as to mounting it. They are sensitive though. Maybe a dish mount?

To use the circuit for your intended application of driving an A/D converter it would need some modifications.

Ron

 

[MikeMl]

How are measuring the negative voltage? Meter, Scope?
What point in the circuit are you using as the reference when measuring the voltage at point 20?

 

[audioguru]

The circuit has errors:
1) The first opamp is inverting with a low input impedance of only 2.2k ohms. Then it loads down the signal from the mic and attenuates it to about 1/3rd. it should be non-inverting with an input impedance of at least 15k ohms.

2) The LM358 has terrible performance for audio. It is noisy, has a poor high frequency response and a poor output swing at high audio frequencies above only 2kHz.

3) The second opamp is non-inverting so its input signal from the 100nF coupling capacitor swings a few volts negative which is very bad since its absolute max allowed negative input is only -0.3V. It should be an inverting opamp then its input signal can swing negative but its input pin stays at 0VDC.

4) The circuit is missing a peak detector that holds brief signals long enough (20ms minimum) to be clearly seen.

Here are my preamp and peak detector circuits for a VU meter:

 

[Tan9890]

Thank you all..

Mike, I'm using the voltage at point 20 as the input to Atmega32. so that the in built ADC can convert the voltage to digital, and accordingly run the motors.

But i'm getting a -ve output. I'm connecting the points like the LED used in the circuit. Cathode on collector, and anode on Vcc. So, cathode point goes to my controller.

Can anything be done in the circuit itself, to change the output to positive? I've actually made the PCB too, so only small changes can be done..

And here in this link, they're using electret mics but they find out direction properly.. Can anyone explain how this works?

Cornell's Autonomous PeanutBot

My project is the same one.. Only simpler...

So plz give me any suggestions..
Thank you.

 

[audioguru]

But i'm getting a -ve output. I'm connecting the points like the LED used in the circuit. Cathode on collector, and anode on Vcc. So, cathode point goes to my controller.
Can anything be done in the circuit itself, to change the output to positive?

If the cathode of the lower LED is the output then 0V (not +9V) is the common. With the circuit powered from 9V then the output high will be about 5.4V which is too high for your micro-controller unless one LED is blue or white. The signal will never be negative.

And here in this link, they're using electret mics but they find out direction properly. Can anyone explain how this works?

The article explains that "arrival time" is used to determine the direction of the sound. The closest mic picks up the sound first. The furthest mic picks up the sound last. Then the micro-controller triangulates where the sound originates from.

 

[Tan9890]

Thanks audioguru..

yes, i got the triangulation part, but i did not understand the concept behind it..
Can u please explain a bit more? or probably provide me with some link which explains the triangulation properly..

Thanks again..

 

[audioguru]

The micro-controller is programmed to note which mic picks up the sound first. Then it knows the sound comes from roughly that direction. It receives the sound a little later from the other two mics then it calculates the exact direction.