Further to an ealier post about packet radio on a Raspberry Pi, I have been presuaded to give a talk to my local Amateur Radio Club on the Rasperry Pi and radio so I’m pulling my finger out and getting things sorted. If I can get it working the final demo is hoped to be using packet to pass messages to a Pi controlling an electric wheelchair that I’ve been tinkering with for far too long.

TNC-PiSomeone pointed me in the direction of the TNC-Pi project which looked superb, so I had to go and buy one. After a relatively straightforward build, it worked first time, although it was slightly uncomfortable not being able to follow my normal ‘baby steps’ approach to testing – you had to go for broke and hook up a radio and try and start decoding packets – I couldn’t find a way to get any responses from the TNC otherwise. Is this because it runs KISS rather than traditional TNC firmware as my Tiny-2 does?

Incidentally, I did almost choke when reading through the TNC-Pi instructions and came to the bit about xastir and found I’d got a namecheck for another post!

Anyway, so far it does exactly what it says on the tin, and I had my first QSO (with myself) at the weekend between two Pis – one with the TNC-Pi the other with a Tiny-2. I also managed to get a shell login over packet which was neat (too geeky for me) but that might be running before I can walk.

I have a week left to complete my presentation – will hopefully post something here when it’s done, I’m now reading up on the finer points of AX.25, and getting stuff worked out in a nice ordely progression.

Things have moved on a bit since my last post about packet radio on my Pi – I got buried in complications about recompiling kernels to support AX25 and soundmodem and the like, then got distracted by other shiny things so this took a back seat.

A recent conversation hinted that recent releases of Raspbian Wheezy had AX25 compiled in, so this prompted me to have another go.

But first a quick recap of where we got so far, and taking it one step further with a graphical interface for APRS Read More

I’ve just got hold of a Raspberry Pi, and my first thoughts were that it would be interesting to try to get a nice packet radio station working without the overhead of a full computer running it. I’ve experimented in the past with linux based systems but not progressed too far. I regret missing the popular period of packet, which seems to have died in the Internet age, but suspect that there might be some latent interest such as mine with a bit of encouragement.

Prepare your Raspberry

Basic setup following recipe from https://projects.drogon.net/raspberry-pi/initial-setup1/ I used Win32DiskImager and a Kingston 16GB ultimate 100X Class 10 card I would then advise tidying things up following https://projects.drogon.net/raspberry-pi/initial-setup2/ It’s then always good practice to update aptitude and upgrade any packages:

sudo apt-get update
sudo apt-get upgrade

The upgrade command will likely take some time as it recompiles all the upgraded packages, but you’ll be left feeling warm and fuzzy that everything is bang up to date.

Prepare the TNC

To start off with I’m using a hardware TNC and may progress to using soundmodem and a USB soundcard later.

I have a PacComm Tiny-2 Mk2, and I have previously made interface cables for a variety of radios, I also have RS232 cables to connect to PC. Google will help if you need it here.

To confirm everything is working, connect a PC to the TNC, then using a terminal emulator such as Putty check that the radio and TNC are working correctly. When the TNC is powered on you should see a stream of boot text, and you should be able to enter commands to set callsign etc. With the radio tuned to the 2m APRS frequency 144.800MHz you should hopefully see some APRS data packets coming in.

Raspeberry RS232 interface

The UART pins on the GPIO header are at TTL levels and need converting top be able to be used as an RS232 interface. The device for the job is a MAX3232CPE which is  a variant of the MAX232 serial buffer which tolerates 3.3v inputs.

I found a neat shortcut to building my own interface circuit was to buy a ready-made board from eBay – part no JY-R2T it comes complete with 9pin D connector, activity LEDs, a header connector and a short cable that allows you to plug in to the relevant pins on the Raspberry – perfect!

Connections for my interface board to the GPIO header are:

(GPIO)          (MAX3232 interface)
Pin 1 (3.3v) -> VCC
Pin 6 (0v)   -> GND
Pin 8 (TxD)  -> TXD
Pin 10 (RxD) -> RXD

The Debian image we installed will have the UART configured to provide a console on the serial port – we want to be able to use it for our own purposes. If you followed the second Drogon recipe above, we have already commented out the getty line in /etc/inittab, but we also need to change /boot/cmdline.txt – remove the parameters ‘console=ttyAMA0,115200 kgdboc=ttyAMA0,115200’ and reboot.

Finally, for testing the interface, let’s install a terminal emulator and connect to our TNC or a PC running Putty. For the PC a straight pin-pin male-female 9 pin d cable should work. Connecting the Raspberry to the TNC with my serial interface board required a crossover male – female cable where tx and rx lines cross.

sudo apt-get install minicom
minicom –b 9600 –o –D /dev/ttyAMA0

If all goes well, you should have the same console access to the TNC that you had with Putty under Windows.

Well the weather could have been kinder to us, but ot could also have been a lot worse. The ‘usual suspects’ from the Bittern DX Group descended on a site on the cliffs of Trimingham on the North Norfolk coast with two aims – to test the site for use in this year’s VHF Field Day, and if 2m was OK to compete in the Open section of the RSGB March 144 / 432 MHz contest. We knew it was likely to be hard work, but it was one of the contests we could use G2B in and we realise we need to “use it or lose it”.

It was the first outing for my new Clark SCAM 12 mast, and it all seemed to be working well which was great.

I chickened out of staying overnight, but did a couple of stints on Saturday and one on Sunday.

Overall we logged 104 QSOs, mostly in an easterly or westerly direction. I got the most Northerly contact to a GD station, Linda managed to make it into the Czech Republic. So not many contacts, but we hope we will make it up with high distance scores.

I picked up an Icom IC-F3GS VHF handheld transceiver at the NARC tabletop sale on Wednesday – a lovely little radio but it did make me think ‘why do I need another handie’?

Well I suppose it’s as much for the challenge of ‘taking control’ of the thing – I’ve had a great bit of fun researching programming software and cables, and I’ve just managed to reprogram it away from Norfolk / Suffolk ambulance channels onto Amateur 2m frequencies.

And it was a bargain, and it’s a nice radio, and you can never have too many handies?

If push comes to shove I’ll just punt it on to someone else at the next sale, having had my fun.


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