A great tool for microcontroller hacking activities you might want to take on in the future is the Baudrate Converter, a device that automatically detects the baud rate of an MCU-based device you wish to hack. Using this method makes things a lot easier, so you don’t have to detect the actual baud rate using the PC or an oscilloscope – it saves a lot of time and energy and it’s also pretty simple to make.
The usual serial transmission has the Tx line on ‘high’ when idle and a single byte starts with a ‘low’ value (the startbit) and ends with a ‘high’ value (the stopbit). The idea is that, based on a few characters, the device measures the times the signal is ‘low’ and sorts them lowest to highest, detecting the real bit-time.
The baud rate converter uses the ATtiny2313 microcontroller from Atmel and the FT232 USB UART chip from FTDI. The latter supplies the power for the ATtiny. The converter has no capacitors for the crystal and runs at 20MHz using a 3.3V voltage, but it seems to be working nonetheless. The software that makes everything work is written in C and uses the 16-bit timer of the ATtiny extensively. After you connect the unknown serial port and send a few characters via a terminal-emulator, the device will detect the baud rate and the transmission of the bytes will be done accordingly, using the appropriate baud rate. If errors are detected, the converter will repeat the autobauding process.
The device has a detection range from 110 to 115200 and can help a great deal if you encounter baud rate conversion difficulties. The source code is available for released under GPLv3 license and is available for download in the link below (a .hex file is also available).
Baudrate Converter: [Link]