Raspberry Pi Satellite Tracker – GH Tracker Running On A Raspberry Pi 3 B+

I have received several requests to share the image and construction details for the Raspberry Pi Satellite Tracker Interface that we use with MacDoppler as part of the Satellite Stations here. You can read more about the motivation for this project and its initial design and testing here.

This article explains how to put a Sat Tracker together.

The information and software described here are provided on an “as is” basis without support, warranty, or any assumption of liability related to assembly or use. You may use information and software image here only at your own risk and doing so releases the author and Green Heron Engineering from any liability for damages either direct or indirect which might occur in connection with using this material. No warranty or liability either explicit or implicit is provided by either AB1OC or Green Heron Engineering.

Now that we have that out-of-the-way, here are the components that you need to build your own Sat Tracker:

• Raspberry Pi 3 B+ Motherboard
• PiTFT Plus 480×320 3.5″ TFT+Touchscreen for Raspberry Pi
• Pibow PiTFT+ Case for Raspberry Pi (This is the case only)
• Black Aluminum Heatsinks with Adhesive Tape Cooling for Raspberry Pi
• 8 Gb or larger Class 10 micro SD Card with adapter (Link is to an inexpensive 16 Gb micro SD Card)
• Power Supply for Raspberry Pi 5V 2.5A Micro USB Charger Adapter with On-Off Switch

The Sat Tracker image includes a display driver for the specific touch display listed above and will most likely NOT WORK with any other touch display. You will also need a Green Heron RT-21 Az/El or a pair of Green Heron RT-21 single rotator controllers from Green Heron Engineering that are properly configured for your rotators.

If you have not worked with the Raspberry Pi before, it’s a good idea to begin by installing NOOBS on your SD card and getting your Raspberry Pi to boot with a USB Keyboard, USB Mouse, and an HDMI display attached. This will give you a chance to get familiar with formatting and loading your SD card with the Raspbian build of the Debian OS for the Raspberry Pi. I’d encourage you to boot up the OS and play with it some to get familiar with the OS environment before building your Sat Tracker.

Etcher Writing Raspberry Pi SD Card Image

The first step in building your Sat Tracker is to put together the hardware and write the image to your SD Card. Use the enclosed instructions or search the web to find information on how to do each of these steps:

1. Install the Heat Sinks on the Raspberry Pi 3 B+ Motherboard. Make sure your chipset heat sink will clear the back of the case. If it won’t, it’s fine to just install the CPU Heatsink.
2. Assemble your case to the point where it is built up to support the touch display
3. Carefully install your touch display on the Raspberry Pi Motherboard
4. Install the remaining pieces of your case including the nylon screws and nuts which hold the case parts together
5. Download the SD Card image from the link below, unzip it, and load the image onto your SD card using Etcher
   • Version 4 Sat Tracker Image – Requires an 8 Gb or Larger SD Card to load
6. Install your SD card in the slot on your Raspberry Pi Motherboard
7. Connect your Raspberry Pi to the outside world as follows:
   • Connect Two USB cables – one end to the Elevation and Azimuth ports on your Green Heron Engineering RT-21 Controller(s) and the other ends to two of the USB connections on the Raspberry Pi
   • Connect a wired Ethernet Cable to your Raspberry Pi via a common Ethernet Hub or Switch with a PC or Mac that has VNC Viewer Installed. You will need a DHCP server running on the same network to supply your Raspberry Pi with an IP address when it boots. Your router most likely provides a DHCP function.
   • Connect your USB power supply to the Raspberry Pi Motherboard and power it up

Your Sat Tracker should boot up to the desktop with GH Tracker V1.24 running. The touch display works fine for using GH Tracker but its a bit small for configuring things. To make the configuration steps easier, the image comes up running VNC Server. I like to use VNC Viewer on my PC to connect to the Sat Tracker using VNC to perform the steps that follow. Note that both the Raspberry Pi and your PC must be on the same sub-network for the VNC connection to work. I’ve also included the following commands in the Sat Tracker image which can be run from the Raspberry Pi terminal window to make the configuration process easier:

$ setdisp hdmi # Disables the TFT display & uses the HDMI interface
$ setdisp tft  # Disables the HDMI interface & uses the TFT display
$ reboot       # Reboots the Raspberry Pi causing
               # the latest display command to take effect

If you select the HDMI interface, you will find that VNC Viewer produces a larger window enabling you to perform the following configuration steps:

1. First, you need to determine the IP address of your Sat Tracker. This can be done via your DHCP server or by touching the network icon (up and down arrows) at the top of the display on the Sat Tracker.
2. Use VNC Viewer on your PC or Mac to connect to the IP address of your Raspberry Pi. The default password is “raspberry“.
3. Once you are connected, open a terminal dialog on the Sat Tracker, set your display to hdmi mode via the command shown above, and reboot your Sat Tracker.
4. Reconnect VNC Viewer to your Sat Tracker and click on the Raspberry button (Start Menu Button) at the top left of the screen, select Preferences, and run Raspberry Pi Configuration. Select Expand Filesystem from the System Tab. This will expand the filesystem to use all of the available space on your SD Card. You can also change the system name of your Sat Tracker and your login password if you wish. When you are done making these changes, reboot your Sat Tracker.
5. Reconnect to your Sat Tracker via VNC Viewer and select Setup -> Rotator Configuration from the menu in the GH Tracker App. Select the TTY devices (i.e. COM Ports) associated with the Azimuth and Elevation connections to your RT-21 Controller(s) via the two dropdown boxes. You can also configure the operational parameters for GH Tracker at this time. The ones that I use with our Alfa-Spid Az/El Rotators are shown below.
   

   GH Tracker Rotator Configuration

6. Configure your Green Heron Engineering RT-21 Controllers to work with your rotator(s). The settings below are the ones that we use with the RT-21 Az/El controller and Alfa-Spid Az/El Rotators that we have here.
   

   GHE RT-21 Az/El Controller Settings for Alfa-Spid Rotator

   Edit

   Setting	Azimuth	Elevation	Notes
   Park Heading	0 degrees	90 degrees	Set via MacDoppler. Minimize wind loading and coupling to antennas below. Also enables water drainage from cross-boom tubes.
   Offset	180 degrees	0 degrees	Azimuth dead spot is South. Elevation headings are from 0 to 180 degrees.
   Delays	6 sec	6 sec	Minimize relay operation during computer tracking
   Min Speed	2	3	Creates smooth start and stop for large array
   Max Speed	10	10	Makes large movements relatively quick
   CCW Limit	180 degrees	355 degrees	CCW and CW limits ensures predictable Azimuth heading for range around 180 degrees. Elevation limits permit 0 to 180 degree operation. Elevation limits shown can only be set via GHE configuration app.
   CW Limit	179 degrees	180 degrees
   Option	SPID	SPID	Alfa-Spid Az/El Rotator
   Divide Hi	360	360	Rotator has 1 degree pointing accuracy
   Divide Lo	360	360
   Knob Time	40	40	Default setting
   Mode	NORMAL	NORMAL	Default setting
   Ramp	6	6	Creates smooth start and stop for large array
   Bright	2	2	Easy to read in shack

7. Configure the source of tracking data to be MacDoppler (UDP) from the GH Tracker Source Menu. We use UDP Broadcasts with MacDoppler running on the same Mac with VNC Viewer to run our rotator. Finally, press the Press to start tracking button on GH Tracker and run MacDoppler with UDP Broadcast on and Rotators Enabled to start tracking.
   

   MacDoppler Tracking AO-91

8. Once you are satisfied with the operation of your Sat Tracker, use VNC Viewer to access the terminal window on your Sat Tracker one last time, set your display to TFT, and reboot.

The most common problems that you’ll run into are communications between your Sat Tracker and your Green Heron Engineering RT-21 Controller(s). If the Azimuth and Elevation numbers are reversed in GH Tracker, simply switch the TTY devices via the Setup Menu in GH Tracker. Also, note that it’s important to have your RT-21 Controller(s) on and full initialized BEFORE booting up your Sat Tracker.

Most communications problems can be resolved by initializing your tracking system via the following steps in order:

1. Start with your RT-21 Controller(s) and you Sat Tracker powered down. Also, shutdown MacDoppler on your Mac.
2. Power up your RT-21 Controller(s) and let the initializations fully complete.
3. Power up your Sat Tracker and let it fully come up before enabling tracking in GH Tracker.
4. Finally, startup MacDoppler, make sure it is configured to use UDP Broadcasts for Rotator Control and make sure that Rotators Enabled is checked.

The VNC Server on the Sat Tracker will sometimes fail to initialize on boot. If this happens, just reboot your Sat Tracker and the VNC Server should initialize and enable VNC access.

I hope you have fun building and using your own Sat Tracker.

Fred, AB1OC