I have just updated my open source AVR based OBDII scanner to have a bootloader. This allows users to update the firmware very easy through the USB connection. Note that Microchip(PIC) version already has a firmware update feature.
I will be adding support for PWM and other protocols here in the next few weeks. I will also work on updating the website to include more documentation about protocols.
Trampas
http://www.sterntech.com/obdii.php