AVR Tracker – a free open source APRS tracker


It is the English Edition of my blog article, hope to sharing my experience to the ham all over the world.

First of all, it is the copyright issue:

WhereAVR is designed by N4TXI, an open source APRS tracker.

AVR tracker is based on the WhereAVR design , modified by DH3WR, also an open sources APRS tracker.


I had introduced one of the cheapest method to setup an igate, which use Raspberry Pi as the platform.

However, if the tracker side which request commercial products, such as Yaesu VX-8GR or Kenwood TH-D72.It seems not valuable. If you consider buy a tracker kit, why do not consider an open source ARPS tracker?

Moreover, the benefit of an open sources solution, you may modify it according your own when necessary.

For the basic C programming of Atmel AVR MCU, please refer some tutorials in web, I recommend eXtreme web site.

All the related link can be found on the right side.


WhereAVR and it’s Successor – AVR Tracker

WhereAVR is an open source APRS tracker. The author use it for the high altitude balloon activities. If you refer the program code, you will found some code used to control servos via IO Ports.

While I google some advanced setup on APRS4r, I found the AVR Tracker information, although most of information written in German

Please be remind that the MCU pin assignment of the original AVR Tracker is 32pin SMD type. And WhereAVR is 28pin DIP type. Do not confuse with each other.

When compare with WhereAVR, AVR Tracker add more functions:

  • GPS signal valid indicator (pin PD2). It will light when the GPS NMEA string is valid.
  • Enabled ADC, which used as an Input voltage level detector (pin ADC1).
  • Enabled I2C interface, connect to a temperature sensor TMP275 (it removed to reduce the PCB size finally)
  • Add a DIP switch, for more features option setting.



Brief circuit description & remind note

I am using 28pin DIP for the MCU, and schematic diagram refer AVR Tracker. So please refer the different between the pin assignment of 28 & 32 pin packages.

The heat of the circuit is the Atmel ATMega8A MCU, it used the pin ss,mosi,miso,sck connect to a resistor network to form a R-2R DA converter. It generates 4 bit APRS packet.


R-2R DA converter (courtesy of WiKi)

The R11, R13, C10 use to handled APRS input signal. As mentioned before, WhereAVR used on high altitude balloon activities and it receives commands from ground station.

On the AVR Tracker, this part is for future purpose.

And the following is the key note of the AVR Tracker schematic diagram:

  • The R18,R21,Q3 on the right bottom side is unnecessary
  • The R12 is not necessary if your GPS output is RS232 level.
  • R7 2k2 used for Yaesu series handheld connection.
  • The resistor ladder network R-2R use 1% to increase the accurate.
  • The NPN transistor is general purpose one, I use CS9018
  • GPS signal valid LED is Yellow
  • PTT LED use Red
  • Rx LED use Green


Progam download tools

Program download to the MCU request a free software, eXtreme Burner, available from eXtreme site.

The download cord is USBASP, a cheap USB download tool, which available from China electronics market.



Please download the zip file of the hex code from DH3WR web site. There are 2 hex code files request to download to MCU, one for main program, other for the configuration.

We also need setup the fuse setting for the MCU afterward.

The 2 hex code files are:

Main Program code “APRS_AVR_Tracker.hex” , download to the MCU without any modification.

eeprom configuration template file:

APRS_AVR_Tracker_EEPROM_DH3WR.hex . It request to be modify before download to the MCU, a windows base utility available to modify the content, such as callsign and other parameter.

The windows base utility program is the key that I choice to use AVR tacker, rather than WhereAVR.

The utility program (AVR_Tracker_CFG_V1.0b) designed by DL1NOS. It changes the hex values of the Hex file according your parameters.




The features available on AVR Tracker:

  • Callsign
  • Path(s)
  • Static Text

The following information can be various by the speed of the tracker (setting by DIP switch 1-2)

  • SSID
  • ICON
  • ICON List
  • 4 preset APRS Message selected by DIP switch 3-4
  • 6 options by click box

The preset value (50) of the Input voltage detection is OK.


Edit the EEPROM configuration template file

Please use the utility program to open the template file, and change the callsign, SSID to your own, then save as another file name.


Download procedure:

Run the download program “eXtreme Burner ”=> Open Flash, and open the MCU main program. Then Write => Flash to download the program.




Still in the eXtreme Burner, File => Open EEPROM File, load the modified configuration file. Write => EEPROM to download the it to the MCU.



Fuse Bits setting

Please be remind do NOT following the fuse bits setting of screen capture ! The correct value is lo:9f , hi:c9


Ensure click the “write” box of the correspond bits, then press Write button on the right bottom.



The value of screen dump is incorrect


Setting, calibation

For the VR R7, the reference value is 3-4k on the GND side.

DIP switch setting

sw1 = 2 set of SSID & icon selection

  • on set2 (Secondary)
  • off set1 (Primary)


  • When on, the speed of the tracker less than 5km will treated as static object, the PTT period will increase to 7min. Consequently, the PTT period is default one (30sec).
  • When off, the PTT period is default on every 30sec


  • 4 set of APRS pre-defined value


For demo, please visit YouTube VR2XKP channel:

AVR Tracker Demo by VR2XKP


What’s Next

We may treated the WhereAVR as template, and AVR Tracker as a reference, to modify the code to add more features. e.g.:

  • add a ADC temp sensor LM35
  • Tx delay
  • enable the command receiving feature



The American invent APRS and used on amateur radio.

The Japanese add the aprs tracker to ham’s transreceiver, and it makes the APRS activities more popular in recent years.

The popular of open sources programs in German, to let me success on the APRS4r Igate, as well as AVR Tracker in cheap costs. The contribution of the German in Amateur radio also great.

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6 Responses to AVR Tracker – a free open source APRS tracker

  1. DL1NOS says:


    thank you for your translation and test of my program. With your permission I ‘d like to add a link from my page to this article.

    I don ‘t know why the program isn ‘t working with your win7-x64. My latest tests with my win7-x64 and win8-x64 where successfull. Maybe a language problem? Do you get an error message?

    73 de DL1NOS

  2. VR2XKP says:

    Recently found the file AVR_Tracker_CFG_V1.0b was removed from web, I uploaded my copy to share it.


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