raspberry pi vu meter

I have been working on driving an analog VU meter based on the sound going out the Raspberry Pi`s audio outputs. This now works! The music [1] is playing from a Raspberry Pi, with software running on the Pi digitally sampling the peak output audio level and writing that out to an 8-bit digi
raspberry pi vu meter - schematic

tal-to-analog converter (DAC). The DAC output is then used to drive the analog meter. If you`re interesting in knowing how all this hangs together, keep reading. The Raspberry Pi is very capable of generating digital signals using its GPIO pins but an analog meter requires an analog signal. To convert a digital value emitted from the Raspberry Pi to an analog voltage we need a DAC. It`s possible, and rewarding, to build a DAC using discrete components, but it`s more convenient, accurate and reliable if you use an off-the-shelf DAC packaged as an integrated circuit (IC). 5V single supply operation: The AD557 requires just a single 5V supply voltage. This is ideal for the Raspberry Pi where we have 5V power readily available. Many DAC ICs require a supply voltage somewhat higher than 5V making them trickier to use with the Pi. 0 to 2. 55V output: A value of 0 at the input gives 0V at the output. A value of 255 at the input (the maximum) gives 2. 55V at the output. This is easy to work with and think about. Flexible input voltage: The digital inputs accept values of 0 to 0. 8V as "0", and 2 to 5V+ as "1", making them compatible with the 3. 3V digital outputs on the Raspberry Pi. Various GPIO pins on the Raspberry Pi are used to provide a number between 0 and 255 to the data input pins (1 through 7) on the DAC. The power supply and ground for the DAC are provided by the 5V power and ground pins available on the Raspberry Pi...

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