Audio Bootloader for Atmega Microcontrollers
It is possible to load a programm into an AVR-microcontroller over the audio interface of a PC or laptop:
http://www.mikrocontroller.net/articles/SOUNDRX
The bootloader presented here has the following features:
- automatic Baudrate detection and callibration
- works without callibration with 8Mhz or 16MHz sysclk ( possibly 1MHz, not testet )
- very simply hardware circuit: 2 resistors and a 100nF capacitor to connect to the audio line
- only one pin for data transmission needed and an additional pin for a status led
- low memory footprint: 800 bytes
- java program to generate the sound, works on win and linux
As line coding scheme Manchester-coding is used. With this type of coding we achieve only half the transmission speed than with "Flankenkodierung" used in Soundrxtx. Therefore the mean value of the signal is more stable and no calibration potientiometer is needed.
AudiBoot2.0:
- coding scheme changed to differential manchester code ==> works on all PCs with inverted audio out
- ATMEGA8 and ATMEGA168 support
- java programmer with 1/2 speed added ==> possible to generate MP3s ( setup to 320kBit/s kompression )
have fun,
chris