I have been interested in timing astronomical occultations for a number of years and to date I have relied on accurate time signals from Radio VNG, broadcasting at 2.5MHz, 5MHz 8.638MHz, 12.984MHz and 16MHz. In late June 2002 I noticed on the RASNZ website that Radio VNG was to close on the 30th June and I sent letters off to various bureaucrats as suggested on the RASNZ site. Well, there must have been plenty of letters from other VNG users because the closure was postponed until December 2002. A solution was required and a glint of light was found in the form of a note on the IOTA Occultation newsgroup by Geoff Hitchcox, author of KIWI and KEA programs. Geoff pointed out a US$25.00 GPS receiver at the BG Micro electronics store in the USA. A flash of my credit card and it landed on my door step one week later with the final cost of AUS$70.10 Now I am the proud owner of a second hand Trimble SveeSix GPS receiver.
For a full description and technical requirements for the KIWI and KEA time stamp utilities, I suggest you visit Geoff's website, please see the links below.....
This webpage is a record of the device I have built to enable Geoff's KIWI software to talk to the GPS receiver and process time and position data. I think it is fair to say that I am a complete electronics novice and I hope this page will serve to encourage like minded amateurs to build a similar device and join the list of KIWI users.
I had a pretty steep and double sided learning curve to negotiate because I am most familiar with Macs and the programs run on a DOS PC and it has been years since I have picked up a soldering iron. Thanks to my friend Ted Dobosz I soon had the PC under control as well as a quick introduction into electronics and also thanks to Geoff Hitchcox who aided me via e-mail with heaps of advise and encouragement.
The assembly of the interface board had four events that made me laugh when I think back....
One, was when I printed up the data sheets of the two integrated circuits and then very carefully wired them backwards....... careful checking by Ted revealed the error. Two, was when Ted and I reversed the leads and applied power and blew up the 5 volt regulator. I wish we had videotaped the event just to see the look on our faces when the blue flame leaped from the poor little device. luckily we didn't have the two chips or the SveeSix connected. Three, was after I got everything together but it wouldn't talk to the PC. I spent a whole afternoon checking and testing, time and time again and it was very late when I discovered I had not wired power to the MAX233 chip. Ten minutes with the soldering iron and I had established communications via the serial port. Four, I couldn't get the parallel port to work and I had to borrow a printer to test it, and eventually discovered the plug to the motherboard was reversed. add in a recalcitrant PC power supply and a dead floppy drive and monitor and you could say that I had an event filled few weeks.
I designed a nice little case to keep everything in place while the GPS antenna will be mounted on the cover.
After the event with the reversed battery leads I wired in two diodes to prevent similar accidental events in the field. Ted pointed out that there was a 2 volt loss across the diode and only one was required, so the one shown here has been removed
The first morning with everything working. SveeSix and antenna on the window sill listening to the satelites through the trees. I let the SveeSix run for 6 hours to build it's almanac and figure out where it was.
Later I moved outside to get a clear view of the sky to run some tests for Geoff. I was astonished to see the SveeSix find 7 satelites in 30 seconds of startup ...... clever little thing.....
I left everything running and went shopping, leaving clear instructions for Tilly Dog if something went wrong.
The final setup. Ted has loaned me a 486 Toshiba Laptop which runs KIWI beautifully.
To keep everything together I needed a case of some sort and eventually decided to put to use my old school case after 25 years of it sitting in a cupboard. I mounted a hinged shelf to support the PC and Interface Box and there is sufficient room under the shelf for AC adapter and cable, 12 volt DC cable, momentary switch and cable and finaly a piece of red perspex that fits over the PC's LCD to preserve my night vision. The Interface box is screwed down onto the shelf and the PC is held in place by leather straps and button snaps. The shelf is hinged at the rear and is secured at the front by a M6 captive screw.
If you have any questions about this device, please don't hesitate to contact me. My e-address is shown below.
Links for more detailed information.
Geoff Hitchcox's KIWI software. The brains of the system.
Trimble GPS tutorial
Occultation Section - Royal Astronomical Society of New Zealand
Yahoo! Groups : IOTAoccultations
South PacificTime Resources Web Site