The basics are described in the article APRS using the IC-2820 and Open-Tracker+ . This description shows only the specific issues with the TinyTrack-3.
like the OpenTracker the TinyTrak-3 has only a very simplified serial interface. Instead of real RS-232 levels it supports only 0/5V. This may not work or if you are lucky it works. With the IC-2820 it does not work because this rig needs a real serial interface.
Therefore it is neccessary to make some extensions like I did it with the OpenTracker.
But the TinyTrack-3 has some other problems. The PCB is not a good RF design. The clock frequency of the PIC processor radiates like a little transmitter. You can easily receive its harmonics with a 2m band transceiver over 10 to 20 meters distance.
Another problem is the ceramic resonator for the clock frequency. This frequency should be precise enough to give a good APRS packet signal. Therefore a crystal should be used which is also cheap but has a good frequency stability.
The software of the TinyTrack-3 works perfect and without any problems, so I decided to make a new PCB which solves the hardware problems and perfectly operates the genious PIC's firmware.
To get the TinyTrack-3 working with the IC-2820 these modifications have to be done:
To implement all these requirements I have redesigned the circuit completely. The only thing we still need is the original programmed PIC.
This is the circuit diagram of the new RF-improved TinyTrack-3 board.
You can download the EAGLE files here: CIRCUIT DIAGRAM, PCB-LAYOUT
The size of the PCB is 80 x 66 mm which is much bigger as required but fits ideally in a standard metal case. The following pictures are streched.
The clock distortions are shorted to an internal ground plane with ceramic capacitors and blocked by inductors. This design is very quiet and no noticeable RF is radiated.
This new built TinyTrack-3 works perfectly, the software as well as the new hardware.
Here are the cable pinouts to connect the TinyTrack-3 with the IC-2820:
IC-2820's 3-pin DATA plug (GPS data):
|Function||IC-2820 (3-pin data socket)||above TinyTrack-3 board (9-pin Sub-D connector)|
|Ground||ground ring||Pin 5|
|GPS data, IC-2820 serial output||mid ring||Pin 3|
|IC-2820 serial input||tip||Pin 4|
IC-2820's 6-pin Mini DIN (packet plug)
|Function||IC-2820 (6-pin Mini DIN socket)||above TinyTrack-3 board (9-pin Sub-D connector)|
|Signal Ground||2||Pin 1|
|PTT from IC-2820||3||Pin 2|
|Power Supply Ground (-)||Pin 5|
|NF from IC-2820||5||Pin 6|
|Squelch from IC-2820||6||Pin 7|
|NF from TinyTrack-3||1||Pin 8|
|Power Supply +12 volts||Pin 9|