The project presented here is a sensitive sound sensor. The circuit converts sound frequency and outputs DC voltage. The board consists of LM358 OPAMP and LM2907 IC. LM358 is used as a dual-stage microphone preamplifier and LM2907 acts as a frequency to voltage converter. The circuit provides analog voltage output when it detects sound. The output of the sensor is proportional to the audio sound frequency detected through the condenser microphone. The output voltage swings from 3.5V to 10.8V proportional to frequency 330Hz to 933Hz. Output is zero when the sound frequency is below 330Hz. Users may try with other frequency ranges, which can be changed using the following formula, Vo = R9 × C6 × VCC × f. The sensor has better response and accuracy than many sound sensors available on the market. The operating Supply is 12V DC and consumes 20mA current. Jumper J1 and J2 are closed for normal microphone operation.
Accurate Acoustic Sensor – Sound Frequency to Voltage Converter – [Link]