[Elecraft] GPS Shack Clock

[harryweston at beeb.net]

Hi

I use the internet only once a week, and each time download 
seven days of Elecraft digest to read at leisure. I've got a 
bit behind with this and only just read the Email from Jim 
Wiley KL7CC on 8th Jan, message #8 of Vol 9 Issue 8. He is 
interested in a GPS run clock for the shack -- well I have 
one, sort of.

I've been interested in GPS for some time, but a complete rig 
was too expensive, and probably wouldn't have allowed me to 
fiddle about with it anyway. In January this year, from the 
information in a couple of magazine articles, I bought a 
basic GPS module, downloaded a free program for a PIC16F877 
microcontroller, and now have it rigged up on a breadboard 
with an LCD display of time and lat/long. 

The PIC, breadboard and LCD are on an 'Icebreaker' device I 
built from a kit, early in 2001, to run PIC programs and 
debug them from a PC. Special software built in to the PIC 
allows you to single-step etc and observe the registers and 
memory as you go, useful as I had to jiggle the program, 
which was originally for a PIC running at 3.2768KHz, to suit 
the 20MHz PIC on the board to get the timings right, but then 
it was a doddle to get the GPS module going. With 5v supplied 
it was away and immediately displayed the time. A couple of 
minutes later it had latched on to the required number of 
satellites and told me where I am (for % read 'degrees' as I 
don't know how to do a degree sign here) -- 50%47.xxN and 00%
40.xxW. I've used xx since the accuracy here, about 20 metres 
for the last digit, would identify my house, and paranoia 
dictates that I like to know who knows where I live.

All this, not counting the Icebreaker which I had anyway, 
cost me under 60GBP plus a few phone calls to sort out some 
details of the GPS module. I intend to transfer the program 
to a stand-alone PIC and put it all in a box and have my own 
home brew GPS set. It would be very easy to adapt it to a 
large LED display of the time -- I visualize having the GPS 
module as a plug in board that I can use to calibrate the 
clock or put in the portable GPS box.

The GPS module I have is a Holux P210 device, about 2" by 1 
1/2" by 5/8" with an internal antenna that works even indoors 
here underneath the water tanks in the roof. It has a 'power 
on' LED which blinks when a good signal is being received, as 
it is as I type, and it gives out a nice stream of ASCII 
characters in various standard messages, identified by an 
initial header, easy to re-format for the display. One 
message is the RMC (Recommended Minimum Content) which looks 
like: 

$GPRMC,161229.487,A,5047.3176,N,00040.1234,W,0.00,000.00,12020
5,...

where 161229.487 is UTC ddmmss.sss, A is 'data valid', 50 to 
W is lat and long, and 120205 is the date. '...' is a 
checksum and other fields. The last two digits of lat and 
long vary all the time, but they are the order of 2 metres 
and 20 centimetres, a bit optimistically. All in all it is a 
fantastic little gadget.

This is getting to be a long email, forgive me if it's all 
old hat by now, so I'll close it with these references. The 
magazine articles are in 'Everyday Practical Electronics' 
(EPE) http://www.epemag.wimborne.co.uk, Jan 2004 page 64 for 
an article about interfacing GPS to PC and PIC that gave me 
the free program, and Jan 2005 page 12, an article about 
using GPS to locate traffic speed cameras that gives details 
of the GPS module. It is an excellent magazine, full of 
exciting projects and technical knowhow. Holux is at 
www.holux.com.tw, but the P210 does not appear there, you 
need to enquire. Icebreaker is another EPE kit, now sold by 
Magenta at www.magenta2000.co.uk. at about 38GBP.

Usual disclaimer -- I've no interest in these sites and 
products except as a satisfied customer -- and a warning: you 
do need to do a bit of research as some of the information 
I've found is misleading, so take care.

Maybe that was all a bit far off topic so I will also say I 
have built K2#2378 with most extras except the 100watt ones, 
and an XV50 transverter, all worked first time, and there are 
a KX1 kit and several other small Elecraft kits on my bench 
waiting to be built. Life is good.

73 and a big thank you to Elecraft and all on this reflector,

Harry M1ETU and M0SOP