HARDWARE

Failure is a new success. When I originally built the audio player, I didn’t have enough RAM, and I failed to fully address the problem at the time. Fortunately, I eventually came up with a solution.

For this project, there are a few requirements for the microcontroller. You need at least 40 KB of flash memory and at least 40 KB of RAM. You also need one SPI for the SD card interface, a fast SPI capable of handling at least 16-bit data for the I²S interface, and one UART or other communication channel for connecting to an external system. A few different microcontrollers will work. Philips’s LPC2148 and Atmel’s AT91SAM7S256 are the most popular. The latter has an SSI module with built-in I²S mode. The Philips microcontroller has a Texas Instruments DSP mode. It’s no surprise that most audio codecs from Texas Instruments support its data interface with a glueless interface to the SSP on the LPC2148 microcontroller. For more generic solutions, you have to modify it to use the I²S. For that purpose, I’ve used some of the microcontroller’s modules: Timer1 in Counter mode (with external input and output to provide LRCK for DAC) and PWM to generate MCLK for the audio DAC.

If you want to use an operating system in your application, then you’ll need an extra timer. If your application has any other user interface, you might need some extra I/O ports.

Two extra prototype boards were attached to the Olimex LPC2148 evaluation board. Let’s take a closer look at each one.