# Measure decibels using a piezo

Yesterday, I found this project:
http://www.nerdkits.com/videos/sound_meter/

I've looking for ways to measure the enviroment sound in a simple and cheap ways, without spending money in professional sound sensors.

If somebody could give some tips on how to aproach the project. I also don't know the code used.

My idea is to measure the enviroment decibels, i don't need to display them in a lcd screen or a LED bar.

Thank you,

It is easy to get a microphone, amplify the sound signal, capture the peak levels and drive some kind of led bar graph display.

Actually calibrating this to correspond accurately to decibels over a range of loudness and frequency is a non-trivial problem which you are not going to be able to accomplish without professional equipment.

Actually, it is not a “professional sound sensor” that you need. Any useful microphone , even quite cheap one, is capable of converting the “sound pressure” into voltage. That’s what microphones do.

It is reasonably straightforward to build a circuit with a microphone, an amplifier with a stable gain, an ADC and a program on the arduino to capture the peak voltage level of each sound oscillation, which corresponds to the fluctuations of the air pressure due to the sound waves.

The problem then, is calibration.

You could then borrow a decibel meter from somewhere, make a whole series of experiments where you measure the voltage level with your device, and the decibels with the sound meter. Provided you can then establish a systematic and reproducible correlation between the two sets of readings, there is your device calibration done.

The main “catch” with this, is going to be the capability of the microphone and gain response of your circuit at very high and low frequencies.

I've tried to use this sensor:

But I wasn't able to measure enviromental noise in decibels, after talking with experienced people. I finally discover that this type of sensors only reacts to loud noises (clap, shout) and it's not omnidirectional. This means that can only read sound that comes froma certain direction.