Tuesday, December 17, 2013

The kernel of an Arduino audio player

The vs10x3 DSP chips allow you to decode or encode various audio formats. This includes codec to mp3, ogg vorbis, as well as decoding flac and support for many other formats. So naturally I took the well trodden path and decided to use an arduino to build a "small" audio player. The breadboard version is shown below. The show is driven by the Uno on the right. The vs1063 is on a Sparkfun breakout board in the top of image. The black thing you see to the right of the vs1063 is an audio plug. The bottom IC in the line on the right is an attiny84. But wait you say, don't you already have the Uno to be the arduino in the room? But yes I say, because the attiny84 is a SPI slave device which is purely a "display driver" for the 4 bit parallel OLED screen at the bottom. Without having to play tricks overriding the reset pin, the tiny84 has just enough for SPI (4), power (2), and the OLED (7) so it's perfect for this application.

The next chip up from the attiny84 is an MCP23017 which connects to the TWI bus and provides 16 digital pins to play with. There is a SPI version of the muxer, the 23S17. The muxer works well for buttons and chip selects which are not toggled frequently. It seems either my library for the MCP is slow or using TWI for CS can slow down SPI operations where selection/deselection is in a tight loop.

Above the MCP is a 1Mbit SPI RAM chip. I'm using that as a little cache and to store the playlist for ultra quick access. There is only so much you can do with the 2kb of sram on the arduino. Above the SPI ram is a 4050 and SFE bidirectional level shifter. The three buttons in bottom left allow you to control the player reasonably effectively. Though I'm waiting for my next red box day for more controller goodies to arrive.

I've pushed some of the code to control the OLED screen from the attiny up to github, for example at:
I'll probably do a more just write up about those source files and the whole display driver subsystem at some stage soon.

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