Free GPS and a Merry Christmas

 Season's greetings to one and all.

I've been fascinated with GPS and GNSS in general for quite some time now, it feels rather miraculous that, for only a few pounds, I can buy a module not much larger than my thumb that will reliably provide my position anywhere on the planet to within a few metres by receiving signals from flying atomic clocks several thousand miles above my head.

I've probably got far too many GPS receivers but recently someone posted an offer of free for the cost of postage receiver modules to the GQRP mailing list and it was too good an offer to turn down. 

A few days later some nice little Leadtek modules arrived, complete with coax pigtails.

As well as the modules, there was a zip file with pinout for the 1mm (?) pitch connector on the underside and a datasheet for the module itself.

While they're quite old, they have a SiRFStar chipset which is a decent performer and I've always found them to be reliably fast to get and hold a fix.

 Unfortunately the antenna connector is not as common as SMA, nor is it an easy one to fit  and the 1mm pitch data connector is difficult to track down at a resonable price so, I opened one up, removed the board and, after a few minutes with magnifying glass and a multimeter, I worked out and made a few changes. 

 The push fit antenna connector got desoldered and replaced with a PCB mount SMA, then tracing the basic, necessary connections,, VCC, GND and TXD, I patched in a 0.1" header to make it easier to connect up.

I'll modify the tinplate enclosure to suit and solder the board back in later. 

I also checked to see if the module sources power for an amplified antenna and sure enough, 3.3V is present on the centre pin.

Connecting it all up to an external antenna and monitoring with PuTTY I immediately saw NMEA strings at 4800BPS, 30 seconds or so later the UTC time field populated which indicates it's 'seeing' satellites and is trying to lock, shortly after that I got accurate position data!

So now I know it works, what to do with it?

I've been tinkering with some STM32 chips for a while and really quite like them, I find the STMCube IDE 'fits' my head and I've developed, ported, generally modified or written various bits of software but never really completed a hobby project so it seems like a good opportunity to make use of these modules and make something useful.

Fitting nicely into my fascination with positioning via GPS I figured it might be quite useful to have a display of Maidenhead locator, calculated and updated in real time as I walk or drive about, useful for /p and it might even encourage me to try some POTA in the new year.

After a few 'learning opportunities' (read annoying, frustrating gaps in my knowledge that took far too much time to fill) this is the result:

 

Now I need to do is work out battery power, create a PCB and enclosure to 3d print. (which sounds a lot, but will be much less effort than the code).

(it will work with any GPS or other GNSS module that outputs standard NMEA strings)