Friday, February 26, 2016

The Gumstix Pi GPS Project Chapter 1: Break it out and get it running

As my first gadget project as Gumstix Guru, I'm going to connect a Pre-GO PPP GPS to a Raspberry Pi Compute Module by way of the Gumstix Pi Compute development board, pictured below.

Getting Started

I could just build a board in Geppetto with the GPS connector on it, but I've already got my Gumstix Pi in hand.  The Pre-GO communicates over a UART connection, a header for which the Gumstix Pi has.  The trick is that I need to manually rig the connection.  Easy enough.  Let's break out the Pre-GO's header:

I made a point of labelling each one of the wires just to make life a bit easier later on.

Of minor concern is the fact that the pitch of the Pre-GO's header is considerably smaller than that of the dev board's UART header so I had to use a finer gauged wire.  Not a big deal but they aren't a good fit for my jumper wires.  My solution?  Easy:  Fold 'em.

Next I decided to forgo the extra mess of jumper wires and go straight to the jumpers.  A nice way of keeping the rat's nest to a minimum.  Oh, and my labels fell off.

First Power-Up

At this point I'm very excited.  The board's all hooked up, the Pi module is in place and it's time to plug it all in.  Hope I didn't forget anything!
Once Raspbian is up and running, I go hunting for my GPS module to no avail.  What's wrong?  Why isn't it working?

Time to go to the test bench to make sure the module works. 
  • Board configured for 3.3V - check
  • Connectors attached correctly - check
  • Waveform resembles data output - check
So I hook it up to an FTDI-UART adapter and check its output.  Looks like GPS data to me:

The Verdict

Okay so the Pi is working and the GPS module is working, they're just not talking to each other.  So the UART header isn't configured correctly.  I'll get that sorted out later.  For now, I'll just hook it up with the FTDI adapter and get some results.

Next Up:  Raspberry Pi CM and GPSD