Sound / Audio Level LED Meter

Here is a project of a sound / audio level LED meter circuit. It can be used as noise meter, loudness meter, sound pressure indicator or VU level meter and also for variety of other related tasks. The circuit is using an electret microphone to detect sound and shows visual indication of LEDs.

This sound to light LED project is using 36 LEDs, 15 transistors and other components. The main circuit of sound detector, amplification and controlling is built around first 3 transistors which are Q1, Q2 and Q3. The electret microphone detects sound signals and changes them into electrical audio signals, these electrical audio signals are then amplified by the transistor Q1 and Q2. The amplified audio signals at the collector of the transistor Q2 pass through the 10uF filter capacitor and rectified by diodes D1 and D2 which converts these signals into DC signals. These DC signals are fed to the base of the transistor Q3 making it switch ON. The transistor Q3 also controls the other 12 transistors Q4 to Q15 according to the DC signals received from the diodes D1 and D2.

The circuit is quite sensitive due to which it can be used for many purposes like for example it can also be used as a sound origin direction finder etc. The sensitivity can be controlled by adjusting the 100K variable resistor or you can also use a 100K potentiometer. For more decreasing the sensitivity you can also use a higher value variable resistor or potentiometer in the place of 100K like 200K or 300K etc.

The operating voltage of the circuit is 12 volt DC. But you can also operate the circuit with 9 volt DC. For doing so use 2 LEDs in the place of three in each line and change the current limiting resistors R7 to R19 to 180 ohms.

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