Monday, June 10, 2013

Stratum 1 NTP server with Raspberry Pi

Using the GPS board I recently mentioned, and a Raspberry Pi, I built a stratum 1 NTP server. I'm working on a writeup of the process, in the meantime, here's a photo of the setup.

The red wire is used to bring the pulse-per-second signal to the Raspberry Pi GPIO connector (in this case, GPIO 18, but you can use a different line if that is already in use). The GPS is powered by the Raspberry Pi via USB, this also provides a ground return path for the PPS signal. At the same time, the GPS boards appears as /dev/ttyUSB0 to the operating system on the Pi.

Thursday, June 6, 2013

GPS board

I got a GPS board in the mail, with PPS output, as well as NMEA output over USB, RS232 and Bluetooth. The plan is to build a basic NTP stratum 1 server to use at home.

Someone wrote a detailed review of this board.

A couple of photos of it on my workbench:

You can view the NMEA data on the terminal window, in this case it was being read over Bluetooth, the USB cable was just providing power.

Friday, March 22, 2013

Wednesday, March 20, 2013

SDR kit inventory

Inventory complete... looks like everything is here, I can't put this project off any longer...

Sunday, March 10, 2013

New project! An SDR kit

Next project is the SoftRock RX Ensemble II Receiver Kit. I've some travel coming up, but I expect to start it in another week and a half, or so.

There are also the assembly instructions.

aprx on the TNCPi

Once the TNCPi has been assembled, attached to the Raspberry Pi and tested, getting aprx running on it is fairly straightforward.

1) Install the subversion client:

sudo apt-get install subversion

Fetch the aprx sources:

svn co src
cd src/trunk
./configure && make clean all
sudo make install

2) Configure aprx

Refer to the aprx documentation for full details and sample configurations, available at aprx's home page and keep the following in mind:

  • The name of the serial device is /dev/ttyAMA0
  • Baud rate is fixed at 19200

Note: this is the data rate for the serial interface between the Raspberry Pi and the TNCPi, the RF data rate is fixed at 1200 baud.

The file to edit is /etc/aprx.conf

3) Run it!

To test the configuration, you can run aprx as follows:

aprx -i -vvv -ddd

The switches are:
  -i makes it interactive rather than background
  -vvv makes the status messages very verbose
  -ddd makes the debug messages very verbose

You can stop aprx with ctrl-C to make changes to the file, then start it again with the same command.

There are sample startup scripts in aprx's documentation that you can use to build one to suit your needs.

Once you have the configuration right, you can start it in the background simply by typing:


Saturday, March 9, 2013

TNCPi build complete

I built a TNCPi, which as the name suggests is a TNC for the Raspberry Pi. It has the same footprint as the Pi, takes power from it, and plugs straight into the GPIO pins.

The TNC appears as a serial device on the Pi, /dev/ttyAMA0, with the data rate fixed at 19200 baud, and the on-air data rate is fixed at 1200 baud.

Note the DB9 connector on the photo: it's used to hook up the radio.

It even worked the first time I powered it up! Assembly is a breeze, I'd call it a one evening project. Only basic tools are needed, and the documentation is good. All of the components are provided with the kit.
Hello, world.