|"The purpose of this project was to create a sound player that can play high quality sound using nothing but a single chip (plus an SD card for data storage).|
The chosen microcontroller was the PIC12F1840. It was chosen because of its fast clock rate (up to 32 MHz). Since microchip PICs have this atrocious property of executing one instruction every four clock cycles, this results in 8MIPS performance. The second reason for the choice was the hardware SPI module - bit-banging SPI is not hard, BUT doing it fast enough to sustain the sound playback would be - the hardware SPI module helps by allowing the SPI clock to be as high at 8MHz without using nearly as much CPU time as bit-banging would. The reset of the circuit design was easy: the PIC outputs a PWM waveform to drive the speaker, which is amplified by a MOSFET, PIC's SPI controller talks to the SD card, and another GPIO is used to provide power to te SD card allowing it to be powered off and thus letting the circuit sleep in very low power mode (nanowatts of power used). The pic is overclocked using the OSCTUNE register to 33MHz from the stock speed of 32MHz."