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Crownhill Associates ZX4120 Adaptor
The ZX4120 module is the smallest that I have experimented with so far, and the cheapest.
Although you do not get an integrated antenna, external antenna are quite cheap these days, so
all in all it seems a good deal. The company's website is [here].
I haven't had the chance to evaluate long term performance yet
but will post any comments in the forum.
You can get the CameraWatch2 .hex file for use with this module [here]. The standard .hex file will not work,
because the Crownhills module runs at 9600 rather 4800 baud. If you already have a programmed PIC, you can just download this file
using the bootloader - you do not need a PIC programmer.
There are some notable differences between this unit and the Holux or RF-Solutions ones,
and these need to be dealt with if you are considering using this unit in the CameraWatch-2
project. It operates at 3V, has a 0.05" pitch header for interfacing and transmits NEMA data
at 9600. The last problem I can deal with by changing the CameraWatch-2 software. The first two
will require some support electronics.
There are many ways to generate a suitable 3V supply to the unit; I have used a cheap linear regulator, the LM317. The input voltage
to this can be from 5V to 20V and we are supplying 5V on the cameraWatch-2 unit. The current consumption is low enough
that a heatsink is not required.
Connecting to the fine pitch header is a bit of a challenge. The PCB design shown here brings the necessary pins out to 0.1"
header pins, which are much easier for the hobbyist to wire to. The PCB can be etched by hand with moderate skill,
or you can use the Gerber files to have a board professionally manufactured. If there is enough interest I may consider
getting a batch made. The board shown here was etched by hand, using Press'n Peel artwork transfer and ferric chloride.
[Click here to enlarge]
[Click here to enlarge]
The circuit itself is very straight forward:
[Click here to enlarge]
The PCB is single sided and uses through hole components, all easily available through normal suppliers such as Farnell.
The source files to the PCB, in Eagle cad format, are available [here]. A freeware version of Eagle CAD can be
downloaded from CADSOFT's website [here]. I recommend it - it's an excellent program. If you prefer you can print the board
artwork from this PDF file [here], although I haven't tried this myself and you may have to be careful with scaling and print
options.
The diagram below shows how to connect this board to the CamerWatch-2 unit. All connections go to the GPS module header JP9. The ZX4120 has an optional
backup battery; I dont yet know how useful this is considering that the other two modules from Holux and RF-Solutions do not have one.
[Click here to enlarge]
Parts list
| Reference | Value |
| C1 | 100nF 0.2" pitch |
| C2 | 1uF 16v 0.2" pitch |
| R1 | 240 0.25W |
| R2 | 390 0.25W |
| IC1 | LM317 TO220 |
Update
I have created a slightly modified version of the board using the much smaller TO92 packaged LM317. The layout is almost identical, with
just the regulator changing. You can get the pdf of the board [here] and the eagle cad files [here].
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