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In the 1980s, there was no internet as like today and so the sources of entertainment were televisions, radios and cassette players. When I was a kid, we had an audio cassette player. We used it to play songs but my imagination was always fixed to its VU meter display with its fancy readings as shown below. It changed with the volume of the speakers and matched rhythmically with the sound coming out of it. During my engineering career, I got to know about the Decibel scale and sound pressure measurement. It soon became a goal for me to design an audio dB meter and recreate my child memories. In this tutorial, I will show how to make a dB meter that is accurate enough for general uses.

Background and Application
Sound needs a medium for propagation or travel. It can’t travel in vacuum. Normally air is that medium but sound can also propagate in liquids and other states of matter. I am not going to lecture on how sound travels and its properties as Wikipedia details everything well here. Everything we see around us has a measurement and a unit. In case of sound pressure, the unit is decibel. Our basic requirement is to be able to measure Sound Pressure Level (SPL) in decibel scale with a typical 8-bit microcontroller, an ordinary microphone and without involving complex algorithms.

Measurement of sound has a number of uses. For instance, monitoring sound pollution, security system, monitoring the quality of an amplifier, detecting sound profile of an environment, etc.”

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