In Part 1 of this series we looked at piecing together the hardware required to get the Raspberry Pi computer in a small form-factor mobile setup. In this part, we will look at utilizing the Raspberry Pi as a TNC front-end for my Kenwood D710 radio. This part assumes that you have the hardware described in Part 1, or its working equivalent. It is also assumed that you have a working Raspberry Pi complete with a copy of the Raspbian OS. This article was written based on Raspian Wheezy & updates current as of 1/27/13; however, due to the simplistic nature of terminal operations, any OS complete with a terminal emulator will suffice for this test. As with Part 1, click on the thumbnail pictures in this writeup for their full-size version.
In addition to the equipment described in Part 1, you will need:
1) A cable to connect from the COM port on the rear of the TM-D710A control head to a standard DB9 serial connector
2) A USB-serial adapter. I used one with a PL2303 chipset, which is well supported under Raspbian, but others may also suffice.
3) A Kenwood TM-D710 radio. Obviously, you can substitute another packet-capable radio such as an FTM-350 or a TS-2000, or any radio connected to an external TNC like a KPC-3+; however, this writeup will use the D710 as the example configuration.
BOOTING THE PI
Once you have the Pi configured, you'll want to power it on (it only takes a cell phone charger with a micro-USB connector to power the Pi). Once it boots, you should see the desktop looking something like this:
You may get a prompt asking you if you want to install the software and its dependencies. Simply type "y" and hit enter and the software will download and install. (This assumes you have a working internet connection on the Pi before you begin.)Code:sudo apt-get install minicom
Once you have minicom installed, you will need to configure it to use your USB-serial adapter. Before you begin this process, connect the cable to the rear COM port on the D710 control head, then to the USB-serial adapter. Plug that USB cable into the Pi somewhere and proceed to configure minicom. When you initially run minicom, you'll want to use the "-s" tag, which simply tells minicom to enter the "setup" mode prior to launching:
Once minicom opens, you should see the following screen (or something like it):Code:sudo minicom -s
Read through the text that scrolls after you hit enter and you will see something like this:Code:dmesg|tail -n 30
This means that your USB device is "/dev/ttyUSB0"...go back to the minicom setup and type that into where you selected "A" on the serial device setup. Once you have done that, hit ESC until you are back at the main minicom setup menu. Scroll down to "Save setup as dfl" and select that. This will save the configuration change you just made as your default configuration so it will automatically come up next time you start minicom. Next simply select "Exit" which will take you out of the minicom setup menu and into the main minicom program.Code:pl2303 converter now attached to ttyUSB0
If all worked out the way it was "Just Supposed To Work" you should see the following screen:
The first thing you will want to do is configure your TNC to get it on the air. The most common mistake made is to fail to set the TNC MYCALL parameter, which will keep you from connecting to any other nodes. Reference your specific TNC manual to see what commands are specific to your TNC setup, but for the D710 simply type (where you replace N0LID with your own callsign/SSID):
The TNC should accept this command. You can check that it took by simply typing "MYCALL" and the TNC will return the MYCALL setting. You may want to setup other parameters on your TNC (turn on your mailbox, enable digipeating, handle UI packets, etc.). That is beyond the scope of this discussion, but there is plenty of information on the net available to get you headed in the right direction.Code:MYCALL N0LID
I set up the D710 for the 2m packet repeater:
Once I got my TNC configured the way I wanted, it was time to connect to the White Tanks 145.71 packet repeater. The node's callsign is W7MOT-6 and its alias is WHTNKS. You can connect by typing either:
at the "cmd:" prompt of your TNC.Code:C WHTNKS
Using minicom I was easily able to log into the WHTNKS node, and from there jump up to UNION2, UNION, HUMBBS, and even ELDEN nodes. This is a snapshot of me rooting around in the WHTNKS node:
Feeling adventurous, I reconfigured the D710 TNC to 9600 baud packet mode:
My test of the Pi as a mobile computer TNC front-end was a resounding success. Granted, the test wasn't really that difficult, but I validated the Pi supports USB-serial adapters (at least with the pl2303 chipset), minicom terminal emulator works when compiled for Pi, and the computer is capable of handling the workload (minimal though it may be.)
Of note, I had to re-configure the display on the Pi terminal to allow me to more easily read the text on the 3.5" screen. I boosted the font size in the terminal from 12 to 16 point font and it seems to work OK for my eyes, although max viewing distance at that size is still only about 3 feet. For longer planned packet operations, I would definitely take the time to get a larger & higher resolution display to avoid eye strain.
Also of note, the touchpad on the keyboard I purchased seems to have a glitch where it gets the cursor stuck in the menu bar at the bottom of the screen. I had to add another regular USB mouse to the Pi to get the cursor in the GUI to work properly. I will troubleshoot this matter and report back when I solve the stuck cursor issue.
Stay tuned for Part 3 where we test the Pi as a software packet TNC using the Linux soundmodem package.
Until next time...