Car GPS System

My latest project is a GPS system for my car, thats so last you I hear you all saying, but wait its not a navigation system but a replacement for the speedometer and a tracking system.

I use a regular GPS system quite a lot and a while ago I noticed that the speed it was reporting was different to what my car was reporting, the difference was fairly big at high speeds, for example driving at 70 mph the car reports it as 76 mph. It was at that point I thought it would be a good idea to have a digital speedo which used a GPS system to calculate the speed. I looked around and found a system which offered this, it was a small box which sat on the dashboard and projected the speed onto the windshield as a head up display; I can't remember the exact price but it was around £50, not to expensive but not worth it for something unimportant.

That was a year or two ago, recently I was looking at GPS modules online and decided it would be fun to make my own, with that in mind I devised the following system.
My GPS system would consist of 3 parts, the main GPS unit, a speed display and a tracking system.

Main GPS

The main unit would house a high sensitivity GPS unit (LS20031), a microcontroller (PIC 18F2620) and possibly a bluetooth module. The microcontroller would receive the GPS data and extract the important information, speed and location, it would then make this available in a simpler form over a serial link. I may also include a bluetooth module which would transmit the raw GPS signal, this could then be used by other devices such as a phone or computer.

Speed Display

The speed display would be just that, a 7 segment led display which would receive the simplified speed signal and display it.

Tracking System

The final module is the tracking system, this would receive the location information and using an inbuilt gsm module relay the data to a server which would store the information. I have had an interest in location systems for a while and since a personal GPS tracker is impracticable because of power consumption issues I can at least track my car, it could even be useful if it gets stolen.

I tend to loose interest in projects quite quickly, especially the more in depth ones which is why I decided on the modular approach, even if I only complete two or one of the parts it is still a usable system.

Progress to date

Over the past few days I have been playing around with an old bluetooth GPS and I have made a lot of progress on the first stage. The module I am using is quite old so internally it is fairly crude which is a bonus for me, it uses a prebuilt GPS module which is soldered to the main board so I have been able to tap into the GPS feed before it reaches the bluetooth module and divert it into a microcontroller.

I have now written a program which parses the data extracting all the information I would need and then outputting it over the bluetooth link, this is perfect for testing as I don't need to have it physically connected to the PC.
None of these parts will be used in the final system, except maybe the bluetooth module if I can remove it from the circuit board, I am just using this setup for testing as I am currently waiting on a high performance GPS module to be delivered.

I decided on a Locosys LS20031, this is a small unit with built in antenna, it seems to be fairly sensitive and has a fast update frequency of 5Hz.

I will post further information as the project progresses