The hardware couldn't be simpler. The power for the ChatPad comes directly from the Raspberry Pi GPIO, the power consumption is very low.
The communication between the two is a standard RS232 (UART) at 19200 baud.
The Raspberry Pi uses an internal clock to generate the baud rate, it is possible to change this clock speed in the /boot/config.txt
file. For this reason, it is essential that this setting remains at it's default for communication to be possible.
Either omit the core_freq=250
or ensue it is set to 250 in the /boot/config.txt
There is a 1K resistor on each data line to restrict the current flowing from the GPIO pins, in case either pin has been configured to an alternate operation.