Stereo Audio on a PIC32

The PIC microcontrollers are powerful little devices, and [Tahmid] is certainly pushing the envelope of what these integrated circuits can do. He has built (for educational purposes, he notes) an audio player based on a PIC32 and a microSD card. Oh, and this microcontroller-based audio player can play in stereo, too.

The core of the project is a PIC32MX250F128B microcontroller. 16-bit 44.1kHz WAV files are stored on the microSD card and playback is an impressive 12-bit stereo audio. It can also play back 8-bit files (with some difficulty). [Tahmid] programmed the interface to work through the serial port and it is very minimalistic, mostly because this was a project for him to explore audio on a microcontroller and wasn’t to build an actual stand-alone audio player that he would use from day to day.

Still, even though the project isn’t ready to replace your iPod, the core audio-processing parts are already done if you want to try to build on [Tahmid]’s extensive work. You could even build a standalone audio player like this but have it play high-quality 12-bit stereo audio!

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The Four Thousand Dollar MP3 Player

[Pat]’s friend got a Pono for Christmas, a digital audio player that prides itself on having the highest fidelity of any music player. It’s a digital audio device designed in hand with [Neil Young], a device that had a six million dollar Kickstarter, and is probably the highest-spec audio device that will be released for the foreseeable future.

The Pono is an interesting device. Where CDs have 16-bit, 44.1 kHz audio, the Pono can play modern lossless formats – up to 24-bit, 192 kHz audio. There will undoubtedly be audiophiles arguing over the merits of higher sampling rates and more bits, but there is one way to make all those arguments moot: building an MP3 player out of an oscilloscope.

Digital audio players are limited by the consumer market; there’s no economical way to put gigasamples per second into a device that will ultimately sell for a few thousand dollars. Oscilloscopes are not built for the consumer market, though, and the ADCs and DACs in a medium-range scope will always be above what a simple audio player can manage.

[Pat] figured the Tektronicx MDO3000 series scope sitting on his bench would be a great way to capture and play music and extremely high bit rates. He recorded a song to memory at a ‘lazy’ 1 Megasample per second through analog channel one. From there, a press of the button made this sample ready for playback (into a cheap, battery-powered speaker, of course).

Of course this entire experiment means nothing. the FLAC format can only handle a sampling rate of up to 655 kilosamples per second. While digital audio formats could theoretically record up to 2.5 Gigasamples per second, the question of ‘why’ would inevitably enter into the minds of audio engineers and anyone with an ounce of sense. Short of recording music from the master tapes or another analog source directly into an oscilloscope, there’s no way to obtain music at this high of a bit rate. It’s just a dumb demonstration, but it is the most expensive MP3 player you can buy.

WAV music player uses an ATtiny

We’re very accustomed to seeing small media player builds, but [txyz]’s ATtiny-powered audio player is one of the smallest and most feature-packed we’ve seen.

The audio player is powered by the very small and very inexpensive ATtiny2313. The music is stored on an SD card – a maximum of 2GB of WAV files recorded in mono at 32kBps at an 8-bit depth. On boot, the ATtiny loads the first audio file from the card and outputs it through a speaker connection.

To make things interesting, [txyz] made the audio player controllable via a serial connection. Once a small FTDI adapter is connected to the player, [txyz] can connect to it through a terminal and run through his playlist.

Even though the player is controllable through a serial port, there are a few pins left over that [txyz] could attach to buttons, if so desired. With a battery pack, this would turn his music player into the homebrew equivalent of an iPod shuffle. With the low component count, it might actually be cheaper than the shuffle, if [txyz]’s time is free, that is.

Video after the break.

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