Raspberry Pi: driving a VU meter using a digital-to-analog converter

As I've mentioned in previous blog articles, my wife and 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!

Here's a video demonstrating the result:

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 digital-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.

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posted: Mon, 06 May 2013 23:40 | permalink | comments

Monitoring Audio Levels with PulseAudio

I'm working on driving an analog VU meter from my Raspberry Pi using whatever audio is going out the Pi's sound outputs. The de facto Linux sound system, PulseAudio, allows any sound output (or "sink" in PulseAudio's nonclementure) to be monitored. In PulseAudio land, each sink has a corresponding "source" called the monitor source which can be read just like any other other PulseAudio input such as a microphone. In fact, to help with volume meter style applications, PulseAudio even allows you to ask for peak level measurements, which means you can sample the monitor sink at a low frequency, with low CPU utilisation, but still produce a useful volume display. When this feature is used, each sample read indicates the peak level since the last sample.

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posted: Sun, 10 Feb 2013 22:05 | permalink | comments

Somewhat over-engineered blinking LEDs

My Raspberry Pi arrived a couple of weeks ago and I've been working on turning it into a mini-audio server to connect to the home stereo in the living room.

As part of the project I'd like to drive an analog VU meter from the sound signal.

This week my (enthusiastic!) wife and I played around with attaching some basic electronics to the GPIO ports so that we could get more comfortable the Raspberry Pi. Our electronics knowledge is more than a little rusty but surprisingly everything we tried worked first go.

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posted: Fri, 20 Jul 2012 13:52 | permalink | comments