Adpcm PIC application
Description:
It is actually possible to use a 8 bit PIC's to reproduce sound but the road is quite long and a bit bumpy.
First of all you will of course need one or more wave soundfiles, not to long though as the files are stored in the PIC's program memory, then you will have to process the sound file(s) with a sound editor eg. GoldWave - trim sound start and stop points, raise volume to max and downsample to the appropriate format, encode to 4bit Adpcm with WinSpeech from Microchip application note AN643 and use my brothers Adpcm2hex software to generate a Basic include file or a C file for eeprom storage (experimental). Take a look in the pdf file below for our recipe.
Download the source code for our helloworld sound file example and try for yourself. We use a R2R resistor network as DAC and an active opamp forth order filter to filter the sound, we will reveal this later.
Below you can see a pictures gallery of the software my brother has made to make an include .bas file for a basic compiler or a hex file for an eeprom to use with an C compiler.
Picture gallery:
Click on the picture to enlarge it and read our comments and advice
The processed C include file with sound data start and stop points.