DORJI Modules – Radio on a Chip

The DORJI modules (DRA818V and DRA818U units) came in yesterday. These modules are full transceivers. They are programmed via UART, don’t require a power cycle between frequencies, have a sleep mode, and can provide 500mW or 1W.

Programming these units is not exactly easy. They use 3.3v TTL levels, so your typical USB to Serial adapter won’t work, as those use RS232 levels (-12v & +12v). TTL levels are typically 0v to 5v, or 0v to 3.3v. Fortunately I intend on using these with a Raspberry Pi, so I will already have a UART (serial interface) that provides 0 and 3.3v levels.

Minicom, screen, PuTTY, and various other terminal clients were giving me a very rough time with these units. The initial handshake command is “AT+DMOCONNECT” with the carriage return and line feed characters. With the terminal programs I listed above, each character was individually sent, and I was commonly seeing “+DMOERROR” as I was trying to type out AT+DMOCONNECT. Python was the tool that finally worked.

import serial
ser = serial.Serial(‘/dev/ttyAMA0’, 9600, timeout=2)

Assuming this all ran correctly, you should see an acknowledgement from the module.

Ultimately this is very exciting, as it’s giving me a full transmitter and receiver on a platform that can be dynamically programmed from a Raspberry Pi. The dynamic frequency changing will allow me to send Slow Scan TV, then send APRS packets, kerchunk repeaters, and then do the whole process again.