Nov 202016

The Yaesu FT-897D has the de-facto standard 6-pin Mini-DIN data jack on the back to which you can plug a digital modem.  Amongst the pins it provides is a squelch status pin, and in the past I’ve tried using that to drive (via transistors) the carrier detect pin on various computer interfaces to enable the modem to detect when a signal is incoming.

The FT-897D is fussy however.  Any load at all pulling this pin down, and you get no audio.  Any load.  One really must be careful about that.

Last week when I tried the UDRC-II, I hit the same problem.  I was able to prove it was the UDRC-II by construction of a crude adapter cable that hooked up to the DB15-HD connector, converting that to Mini-DIN6: by avoiding the squelch status pin, I avoided the problem.

One possible solution was to cut the supplied Mini-DIN6 cable open, locate the offending wire and cut it.  Not a solution I relish doing.  The other was to try and fix the UDRC-II.

Discussing this on the list, it was suggested by Bryan Hoyer that I use a 4.7k pull-up resistor on the offending pin to 3.3V.  He provided a diagram that indicated where to find the needed signals to tap into.

With that information, I performed the following modification.  A 1206 4.7k resistor is tacked onto the squelch status pin, and a small wire run from there to the 3.3V pin on a spare header.

UDRC-II modification for Yaesu FT-897D

UDRC-II modification for Yaesu FT-897D

I’m at two minds whether this should be a diode instead, just in case a radio asserts +12V on this line, I don’t want +12V frying the SoC in the Raspberry Pi.  On the other hand, this is working, it isn’t “broke”.

Doing the above fixed the squelch drive issue and now I’m able to transmit and receive using the UDRC-II.  Many thanks to Bryan Hoyer for pointing this modification out.

Nov 122016

So, recently, the North West Digital Radio group generously donated a UDRC II radio control board in thanks for my initial work on an audio driver for the Texas Instruments TLV320AIC3204 (yes, a mouthful).

This board looks like it might support the older Pi model B I had, but I thought I’d play it safe and buy the later revision, so I bought version 3 of the Pi and the associated 7″ touch screen.  Thus, an order went to RS for a whole pile of parts, including one Raspberry Pi3 computer, a blank 8GB MicroSD card, a power supply, the touch screen kit and a case.

Fitting the UDRC

To fit the UDRC, the case will need some of the plastic cut away,  rectangular section out of the main body and a similarly sized portion out of the back cover.

Modifications to the case

Modifications to the case

When assembled, the cut-away section will allow the DB15-HD and Mini-DIN6 connectors to protrude out slightly.

Case assembled with modifications

The UDRC needs some minor modifications too for the touch screen.  Probe around, and you’ll find a source of 5V on one of the unpopulated headers.  You’ll want to solder a two-pin header to here and hook that to the LCD control board using the supplied jumper leads.  If you’ve got one, use a right-angled header, otherwise just bend a regular one like I did.

5V supply for the LCD on the UDRC

5V supply for the LCD on the UDRC

You’ll note I’ve made a note on the DB15-HD, a monitor does NOT plug in here.

From here, you should be ready to load up a SD card.  NWDR recommend the use of Compass Linux, which is a Raspbian fork configured for use with the UDRC.  I used the lite version, since it was smaller and I’m comfortable with command lines.

Configuring screen rotation

If you try to boot your freshly prepared SD card, the first thing you’ll notice is that the screen is up-side-down.  Clearly a few people didn’t communicate with each-other about which way was up on this thing.

Before you pull the SD card out, it is worth mounting the first partition on the SD card and editing config.txt on the root directory of that partition. If doing this on a Windows computer ensure your text editor respects Unix line endings! (Blame Microsoft. If you’re doing this on a Mac, Linux, BSD or other Unix-ish computer, you have nothing to worry about.)

Add the following to the end of the file (or anywhere really):

# Rotate the screen the "right way up"

Now save the file, unmount the SD card, and put it in the Pi before assembling the case proper.

Setting up your environment

Now, if you chose the lite option like I did, there’ll be no GUI, and the touch aspect of the touchscreen is useless.  You’ll need a USB keyboard.

Log in as pi (password raspberry), run passwd to change your password, then run sudo -s to gain a root shell.

You might choose like I did to run passwd again here to set root‘s password too.

After that, you’ll want to install some software.  Your choice of desktop environment is entirely up to you, I prefer something lightweight, and have been using FVWM for years, but there are plenty of choices in Debian as well as the usual suspects (KDE, Gnome, XFCE…).

For the display manager, I’ll choose lightdm. We also need an on-screen keyboard. I tried a couple, including matchbox-keyboard and the rather ancient xvkbd. Despite its age, I found xvkbd to be the most usable.

Once you’ve decided what you want, run apt-get install with your list of packages, making sure to include xvkbd and lightdm in your list.  Other applications I included here were network-manager-gnome, qasmixer, pasystray, stalonetray and gkrellm.

Enabling the on-screen keyboard in lightdm

Having installed lightdm and xvkbd, you can now configure lightdm to enable the accessibility options.

Open up /etc/lightdm/lightdm-gtk-greeter.conf, look for the line show-indicators and tack ;~a11y on the end.

Now down further, look for the commented out keyboard setting and change that to keyboard=xvkbd. Save and close the file, then run /etc/init.d/lightdm restart.

You should find yourself staring at the log-in screen, and lo and behold, there should be a new icon up the top-right. Tapping it should bring up a 3 line menu, the bottom of which is the on-screen keyboard.

On-screen keyboard in lightdm

On-screen keyboard in lightdm

The button marked Focus is what you hit to tell the keyboard which application is to receive the keyboard events.  Tap that, then the application you want.  To log in, tap Focus then the password field.  You should be able to tap your password in followed by either the Return button on the virtual keyboard or the Log In button on the form.

Making FVWM touch-friendly

I have a pretty old configuration that has evolved over the last 10 years using FVWM that was built around keyboard-centric operation and screen real-estate preservation.  This configuration mainly needed two changes:

  • Menus and title bar text enlarged to make the corresponding UI elements finger-friendly
  • Adjusting the size of the FVWM BarButtons to suit the 800×480 display

Rather than showing how to do it from scratch, I’ll just link to the configuration tarball which you are welcome to play with.  It uses xcalendar which isn’t in the Debian repositories any more, but is available on Gentoo mirrors and can be built from source (you’ll want to install xutils-dev for xmake), stalonetray and gkrellm are both in the standard Debian repositories.

FVWM on the Raspberry Pi

FVWM on the Raspberry Pi

Enabling the right-click

This took a bit of hunting to figure out.  There is a method that works with Debian Wheezy which allows right-clicks by way of long presses, but this broke in Jessie, and the 2016-05-23 release of Compass Linux is built on the latter.  So another solution is needed.

Philipp Merkel however, wrote a little daemon called twofing.  Once installed, doing a right click is simply a two-fingered tap on the screen, there’s support for other two-fingered gestures such as pinching and rotation as well.  It is available on Github, and I have forked this, adding some udev rules and scripts to integrate it into the Raspberry Pi.

The resulting Debian package is here.  Download the .deb, run dpkg -i on it, and then re-start the Raspberry Pi (or you can try running udevadm trigger and re-starting X).  The udev rules should create a /dev/twofingtouch symbolic link and the installed Xsession.d/Xreset.d scripts should take care of starting it with X and shutting it down afterwards.

Having done this, when you log in you should find that twofing is running, and that right clicks can be performed using a two-fingered prod.

Finishing up

Having done the configuration, you should now have a usable workhorse for numerous applications.  The UDRC shows up as a second sound card and is accessible via ALSA.  I haven’t tried it out yet, but it at least shows up in the mixer application, so the signs are there.  I’ll be looking to add LinBPQ and FreeDV into the mix yet, to round the software stack off to make this a general purpose voice/data radio station for emergency communications.

Nov 062016

Sometimes, it is desirable to have a TLS-based VPN tunnel for those times when you’re stuck behind an oppressive firewall and need to have secure communications to the outside world.  Maybe you’re visiting China, maybe you’re making an IoT device and don’t want to open your customers’ networks to world+dog by making your device easy to compromise (or have it pick on Brian Krebs).

OpenVPN is able to share a port with a non OpenVPN server.  When a tunnel is established, it looks almost identical to HTTPS traffic because both use TLS.  The only dead giveaway would be the OpenVPN session lasts longer, but then again, in this day of websockets and long polling, who knows how valid that assumption will be?

The lines needed to pull this magic off?  Here, we have sniproxy listening on port 65443. You can use nginx, Apache, or any other HTTPS web server here.  It need only be listening on the IPv4 loopback interface ( since all connections will be from OpenVPN.

port 443
port-share localhost 65443

There’s one downside.  OpenVPN will not listen on both IPv4 and IPv6.  In fact, it takes a ritual sacrifice to get it to listen to an IPv6 socket at all.  On UDP, it’s somewhat understandable, and yes, they’re working on it.  On TCP, it’s inexcusable, the problems that plague dual-stack sockets on UDP mostly aren’t a problem on TCP.

It’s also impossible to selectively monitor ports.  There’s a workaround however.  Two, in fact.  Both involve deploying a “proxy” to re-direct the traffic.  So to start with, change that “port 443” to another port number, say 65444, and whilst you’re there, you might as well bind OpenVPN to loopback:

port 65444
port-share localhost 65443

Port 443 is now unbound and you can now set up your proxy.

Workaround 1: redirect using xinetd

The venerable xinetd superserver has a rather handy port redirection feature.  This has the bonus that the endpoint need not be on the same machine, or be dual-stack.

service https_port_forward
flags = IPv6               # Use AF_INET6 as the protocol family
disable = no               # Enable this service
type = UNLISTED            # Not listed in standard system file
socket_type = stream       # Use "stream" socket (aka TCP)
protocol = tcp             # Protocol used by the service
user = nobody              # Run proxy as user 'nobody'
wait = no                  # Do not wait for close, spawn a thread instead
redirect = 65444 # Where OpenVPN is listening
only_from = ::/0 # Allow world + dog
port = 443                 # Listen on port 443

Workaround 2: socat and supervisord

socat is a Swiss Army knife of networking, able to tunnel just about anything to anything else.  I was actually going to deploy that route, but whilst I was waiting for socat and supervisord to install, I decided to explore xinetd‘s capabilities.  Both will do the job however.

There is a catch though, socat does not daemonise. So you need something that will start it automatically and re-start it if it fails. You might be able to achieve this with systemd, here I’ll use supervisord to do that task.

The command to run is:
socat TCP6-LISTEN:443,fork TCP4:

and in supervisord you configure this accordingly:

command=socat TCP6-LISTEN:443,fork TCP4:"