Project : APRS in my car

As a radio-amateur, I'm mainly busy experimenting with APRS (when I've some time left ...).
I'm a linux-user and a registered user of UI-View. I made them communicate to each other with ldsped.

I not only want APRS at home, but also in my car. This project describes what I did to acomplish that.



1. building blocks

2. TM-D700

3. GPS receiver

4. Processorboard
  5. Put it all together

6. Conclusion


1. Building blocks

APRS in your car, it can be fairly easy :

  • buy a tranceiver/tinytrack /GPS combination.
  • you want more options & cheaper & want to build/control things yourselves , use opensource : OpenTracer
  • buy a kenwood TM-D700 or similar
  • ...
  • make something of your own.

A tranceiver + tinytrak seems nice, the OpenTracker even better, and if you use a dualbander, you have a voice channel left. Personally, I would go the opensource (opentracker) way and I would build it all myself.
The disadvantage, howerver, is that you can only send APRS data, not receive.

This would be solved with the very nice kenwood TM-D700. The disadvantage here is the problem you have with all universal systems : some features you like, some you absolutely do not want and some you lack.
One of the features I lack on the th TM-D700 is smartbeaconing.

I took the time to search and evaluate several solutions. I like the idea of a car-PC to have a flexible system for music, GPS, APRS, ...
But between thinking/wanting and having lies a big gap (in my case, it may never come to it ...)
Since I was charmed by the kenwood TM-D700, and after many thoughts, I bought one.

I was, on the other hand, been busy making a system to warn me if may car came near some point of interest (POI) as there are : my home, my parents home, and other interesting things :-)
Alternatively, a GSM modem could be connected to question the car's position by sending an SMS.

So, since I already had a GPS receiver and a processorboard (and, in fact, a positioning system), why not go the amateur way and link it with the TM-D700 (and drop the GSM modem) ?

summarizing, my building blocks are :

  • Kenwood TM-D700
  • GPS receiver
  • processorboard
2. TM-D700

As said, the TM-D700 is a nice tranceiver. Kenwood makes fine equipment.
But what I don't like is, they are very very closed about it. It is hard to impossible to get 'low level' information. I do not know why they don't make their equipment more open (for the TM-700 : firmware upgradable, detailed low level interface protocol, easy interfacing, customizing possibility for the display; why not make it possible to set messages on the display via the serial interface, ...).

Several people have done a good job experimenting with the TM-D700 and finding out how to communicate to read/change settings :

This can come in handy further on ...

3. GPS receiver

I got a 2nd hand GPS receiver board (a µBlox product).
It should function well, but I've got a lot of problems with it. Sometimes it takes 15 and more minutes to lock to its position. In the mean time, it may produce some really faulty data.
So, When tracking my car, I seem to travel europe very fast sometimes - and the ocean is not a problem either :-)).
I'm in search for a better receiver ... (a board with the SiRFstarIII would be nice : a TTFF 1 second ! I had a garmin forerunner using this chipset in my hands for some minutes and its really astonishing !).

4. Processorboard

On a fair in Brussels, I saw zworld processor boards. I did some nice projects since, all with those boards.
One of the zworld RCM core modules is the heart of my prototype POI-warn board :

(click to enlarge)

I tend to like the zworld products, but I recently got some severe problems with one of their core modules. It seems to be a construction fault, the Belgian supplier sent me a replacement board, but it had the same fault (I'm not able to program it, although other boards don't give me any problem - the supplier also tested them and has the same problems with those boards). Zworld seems not willing to solve this problem and they seem to let my supplier alone).

Very, very bad points for zworld. If it's not solved in the near future (this problem delays one of my projects severely), I'll switch to other proccesorboards and will leave the zworld products.
Update : the belgian supplier has taken back the module. I do not now if zworld did help them, but I got a module from another batch and this worked well.

For now, this project has a working core module, so I will let it at that.

Elements are (see foto) :

  • power supply : makes 5V out of the car's 12V
  • amplifier : intended to drive a speaker for the POI-warning signal. Now omitted (I removed the components), only the buzzer stayed in place
  • I/O : LED's for status, red & black button to input and clear POIs, DIP switches to set some options of the board.
  • RS232 : one DB9 connector, a 2nd connection via a cable that connects directly underneath the PCB (white cable).
  • processor board : the zworld rabbit coremodule
  • the GPS receiver

5. Put it all together

Finally , I did put it all together.

The board stays the POI-warn board, but the software has been extended with routines to control the tranceiver so it will send our position, if the smartbeaconing routines instruct it to.

I discovered you can make the tranceiver send his position by setting the APRS Tx interval to any value : send 'TXI 8' to the device, this will set the APRS Tx to 30 mins AND will Tx the actual position. By setting the Tx interval at 30 min, no unwanted extra packets are transmitted (at least, not within the next half hour)
Disadvantage is : each Tx, the display will reset to the dual frequency display (so when you are watching APRS stations or messages or ..., it wil instantly switch to the main display). I did not find a solution to this at this moment.

The DB9 connects to the TM-D700 to feed it with the NMEA data. The 2nd serial connection goes to the tranceiver's serial port for the above mentioned control.

The tranceiver & POI board are located in the rear of the car, the TM-D700 panel is in front. The IO of the processorboard is also brought to the front of the car (click photo).

6. Conclusion

OK, I got nearly where I wanted to be : the TM-D700 transmits my position, using the smartbeaconing principle.

The next things to do :

  • make a proper, final printed circuit board
  • make the board switch on and off the TM-D700 when the car is started / stopped.
  • extend the software so that, when the car is switched off, it will switch on the GPS receiver after an hour or so, wait until position lock, switch on the tranceiver, transmit the position, and finally switch all off (handy if the car gets stolen ?).


If you have some more questions/remarks/ideas/corrections/ ... , please tell me about it.