Audio VU Meter using Arduino

Posted on Feb 5, 2014

Hope, you follow my advice and hack your cheap USB speakers, to get nice ( pre-assembled ! ) analog front-end  for this project. If not, than get your soldering iron to work, minimum two resistors and 1 cap would required, assuming you already have display wired up and running. First things with AC measurements ( audio in this category ) on

Audio VU Meter using Arduino
Click here to download the full size of the above Circuit.

Atmel microcontroler is to get rid of negative half-wave of the input signal, and this what front-end circuitry should do. There are at least two option: rectifying AC to DC before voltage could reach arduino analog input, or biasing signal with external DC offset. Rectification, could nicely be done with help of specifically design IC, LM3914 / 15 / 16 for example. But in this article, I`d describe second alternative, as it`d be not fare to ask you to hack your speakers and than tell you to solder another board . Here is my set-up, slightly modified version from last blog: When AC input signal is mixed with DC offset, so it stays always in positive area, ( think about sine, which defined betseen -1 and +1, if I add +1 it always would be positive ), I only save arduino life, preventing it from destruction by negative voltage. When arduino ADC completes conversion from analog to digital form, I don`t need DC offset anymore, and it should be subtracted. 2. Sampling subroutine is running at 40 kHz, that is more than enough for ANY application. You may decrease sampling rate to lower CPU load, with current settings VU metering consumes more than 50%. Higher sampling rate gives better linearity / precision over wide band, the same time with regular audio content even 10 kHz sampling would provide better than 1 dB accuracy. All input capture process goes in Interruption subroutine, which is configured in setup. Two channels of...

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