Building an extremely small ARPS Tracker

1 Project goal

This project has the goal to assemble a lowest possibly imaginable power saving and absolute supercompact highly packed APRS tracKing transmitter. At last, I want to be able to visualize my position...!

2 Ingredients

At last, I got all my ingredients collected:

• EM-406A, a 20 Channel SiRF III GPS Receiver from USGlobalSat with Antenna
• Open Tracker SMT
• Radiometrix HX1-144.800-3 300 mW transmitter
• Comet SMA-501 0dBi 1/4 wave miniature antenna

Still on the breadboard...

Assembly... In other projects I have made excellent experiences with U-profiles that can hold PCB boards. Also in this case I took small snippets of U profiles and soldered them into the base box so they can hold both my carrier boards for the OpenTracker and for the RadioMetrix module.

3 Data

3.1 Datasheets

• http://www.sparkfun.com/datasheets/GPS/EM-406A_User_Manual.PDF EM-406A User Manual
• http://www.datasheetarchive.com/pdf-datasheets/Datasheets-3/DSA-56110.pdf RadioMetrix Module Datasheet
• http://kr.ic-on-line.cn/IOL/datasheet/mc908jl16cdwe_736434.pdf Datasheet for the Microcontroller in the OpenTracker SMT

3.2 References

• http://www.sparkfun.com/datasheets/GPS/NMEA%20Reference%20Manual1.pdf NMEA Reference
• http://wiki.argentdata.com/index.php/OpenTracker%2B

3.3 Other data

The tracker's inner values:

   * Voltage: DC 6.5 to 28V unregulated or 5V DC regulated
   * Current: 8 mA idle, 20 mA transmitting Max 200 mA @ 5 V available for GPS
   * Modes: 1200 bps AFSK (send and receive); 300 bps AFSK, PSK31 (send only)
   * Radio Connector: pin header
   * Serial Connector: pin header
   * Dimensions: 31mm x 18mm x 5mm
   * GPS interface: NMEA in/out 

Pinout:

Pin  Name   Funktion
1    5VIN     Geregelter 5-Volt-Eingang
2    RxD      RS-232 Data in der (vom GPS oder Computer)
3    1Wire    Dallas 1-Draht-Bus für externe Sensoren
4    AOUT     Audio-Ausgang an Radio
5    ADC5     Analog-Eingang
6    T1CH1    Timer-Kanal
7    ADC6     Analog-Eingang
8    RST      Reset (active low)
9    ADC7     Analog-Eingang
10   IRQ-     Transmit-now, Profil wählen, oder Zähler
11   ADC8     Analog-Eingang
12   ADC9     Analog-Eingang
13   AIN      Audio-Eingang von Radio
14   ADC4     Analog-Eingang
15   ADC3     Analog-Eingang
16   TXD      RS-232 Data aus
17   rot      rot LED-Ausgang
18   grün     grün LED-Ausgang
19   ADC2     Analog-Eingang
20   ADC1     Analog-Eingang
21   PTT      Push-to-talk-Signal an Radio
22   REGOUT   Regulator-Ausgang - 5 Volt
23   GND      Ground
24   REGIN    Regulator-Eingang - 6,5 bis 28 Volt

• http://www.jaeger-edv.de/Shop/index.php?page=shop.getfile&file_id=40&product_id=25&option=com_virtuemart&Itemid=53 Config Tool for the OpenTracker SMT

The following picture is from ArgentData:

And here's how to use the USB / Serial adapter from the Arduino projects: http://arduino.cc/en/Guide/ArduinoMini

I am using this adapter to program the SMT chip.

4 Project plan

• Find a cabling arrangement that works on my BreadBoard, using the Arduino USB/Serial interface.
• Program the Opentracker SMT
• Rearrange all the three components on minimal space
• Build a suitable case

5 Progress

• 2009-11-05 I got my GPS box up and running. Produces really nice output. Also got the Radiometrix transmitter up and running. Produces a nice signal. Now I still need to get the OpenTracker up and running.
• 2009-11-07 Well, the tracker is not so small after all, but it still all fits into my palm, and this all includes the battery. The case is now ready and I am just finalizing everything. Still need to program the uC with my callsign.
• 2009-11-11 I heard recently that there's going to be a new APRS repeater in our region (DB0SAD). At last, I can use the device as a counterpart for my APRS node, which is currently inactive: Using the ASUS WL-500gP as a APRS digi
• 2009-11-14 I see that it is necessary to connect RegOut (5V out from the voltage regulator) with the RegIn that expects 5V input. This is necessary that the CPU can run. I also see that the HX1 module and the Tracker just like that won't co-oeprate. The OT+ draws PTT to LOW, but the HX1 expects PTT ro be HIGH (same voltage as Input Power).

6 Tests

• Since I have my APRS relay station ready to go anyway, I just need the tracker to start tracking!