W2DEN’s APRS Tracker using a Teensy 3.1 Microcomputer


W2DEN's APRS Tracker Display

While interest in packet radio waned, hams held onto their APRS capability and hardware. With the ability to use smartphones as APRS trackers and displays, interest is now on the rise. This piqued my curiosity if it was possible to make an APRS tracker from simple, readily available components. Turns out the answer is “Yes’. many have already completed trackers using Arduinos, Raspberry PIs and Teensy microcomputers / controllers. After a ton of research I have settled on creating a tracker with the following attributes:

  • Cheap: Less than $100 including an HT.
  • Reliable: Should work first time, every time.
  • Reproducible: Anyone with a soldering iron and a USB equipped Windows computer should be able to recreate the unit..
  • Portable / small.
  • Universal radio connections: This may be a bit difficult but will try to move any radio specifics into the interconnecting cable.
  • Upgradable: No proprietary hard or software. Open source only. Well documented
  • ??


  1. GPS receiver, marginally portable  ( Link ).
  2. I/O ( Link )
  3. Testing ( Link )
  4. Software ( Link )
  5. Enclosure ( Link )
  6. Resources ( Link )


This is NOT a Heathkit. Nor is it a ‘buy the kit and put it together’ project. You will have to buy or scrounge the parts. Plan a schematic layout and solder the components together. There are no surface mount parts but the lands can get small and getting it right is critical. Do some loading of the sketch into the Teensy. And, finally, you will need to figure out how to fit this into an enclosure of some kind.

There was a day, way back in the history of the ether, when such a warning would not have been needed. Everything was home brewed and shared circuits were not much more than scribbles on a sheet of paper, or perhaps the back of a napkin, most likely made of cloth. While this step by step is a little more modern than those days it still reflects on the, ‘that’s a nice design, let me make it my way’ of thinking.

If you follow along, do some homework, figure out the details of your Teensy Tracker and leave some sweat on the shop floor you will be rewarded with a great project that actually works. Who knows, maybe even spark the inventor’s fuse in you to continue on to other projects.

Let’s get going:


This project is built around  Teensy 3.1 made and sold by PJRC. What’s a Teensy you ask? A Teensy is a micro-controller that is a cousin to the Arduino line of micro-controllers. A controller does not have an operating system, it only runs one program at a time. Not to be confused with a Raspberry PI which is a micro-computer that runs an operating system and can have multiple applications available at a time to run, just like your PC or tablet.

Here is a list of the hardware for this project. This will be a ‘living’ table as the unit evolves. Two columns on cost, one for what is needed to recreate the APRS tracker the other for ‘nice to haves’ (not included in the <$100 cost limit).

Description Source # Tracker Optional Notes
Teensy 3.1 PJRC 1 $22.80 With pins Breadboard / PCB
Display ILI9431 PJRC 1 $8.00 cheap TFT display. Does the job.
Skylab SKM53 GPS nooelec 1 $12.50 Cheapest, functional
78-4n25 M 1 $0.59 Optocoupler
1:1 Transformer M 2 @ $2 $4.00 42TL016-RC 600:600 ohm
0.1 uf disc cap M 4@$.25 $1.00 140-50U9-104Z-RC
Printed Circuit Board RS 1 $3.49 276-170 PCB
RJ45 Jack SF 1 $1.50 Solder for SF Breakout
RJ45 Breakout Board SF 1 $1.95 for SF breakout
micro B Breakout SF 1 $1.95
Rotary Encoder Adafruit 1 $4.50 For the menu Option
Small box eBay 1 $1.95 L*W*H:3.35″2.28″x1.30″ (Link)
RJ45 Jack Lowes 1 $4.91 Punch Down for breadboarding
Project Enclosure RS  1 $6.49 270-106 Project Enclosure
Breadboard PJRC 1 $7.50 Great for experimenting
USB-Micro-B cable PJRC 1 $4.00 If you do not have one.
Totals  — $64.23 $22.90


  • RS: radio Shack: most of these components are no longer available. Substitutes can be found at flea markets, on-line etc.
  • M: Mouser. part numbers are current at the time of the project.
  • L: Lowes
  • SF: SparkFun

Development Environment:

As an Arduino cousin the Teensy will run most Arduino software. It uses a modified Arduino IDE (Integrated Development Environment) system, called Arduino, to develop software, called a sketch, and to load it into the Teensy via USB. Even if you are not developing any software you need the IDE to load the APRS sketch into the Teensy.

Let’s load Teensyduino, the Teensy IDE:

PJRC goes through this step by step, follow the procedure here. We’ll embellish:

Step 1:

Follow the link to the Arduino site and  download the appropriate file. Most likely the “Windows Installer”. Save the “.exe” file the run it to install the Arduino IDE.

Step 2:

Skip unless you are running Linux.

Step 3:

Select the appropriate Teensyduino Installer from the list above Step 1:. If you are running Windows OS also download the “Windows Serial Installer” under “Other Files”.

Run the serial_install.exe if you are running Windows.

Then run the Teensyduino installer.


You should now have the Arduino IDE icon on your desktop. Click it to open the IDE. Now click the Help / About on the menu. It should say Teensyduino with a version number such as 1.23


There is a very good tutorial on how to set up the Teensyduino IDE and run your first sketch called “Blink” located here.

Click on the link and follow the “Basic Teensyduino usage” tutorial.

NOTE: the latest Teensy v 3.1 has the LED on pin 13. The first line in the sketch should read: “int ledPin = 13;”

That’s about it…. you now have the IDE installed and have tested it with your first sketch.

Next: Phase 1: GPS Receiver >>