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New project: GPS tracker

It’s about time for a new project and I’ve decided to dust off an old project that I never really got started: a GPS tracker with a GSM/GPRS phone module.

Sure, there are plenty of GSM enabled GPS trackers available – both comercially (like this one) and as hobby projects (this one for example) but that doesn't mean that I can’t 1) learn a lot from making one myself, 2) have fun while doing it and 3) make something better than what is out there…

Initial requirements

So the initial high-level requirements (aka “what’s it gonna do”) are:

  1. Get current position from GPS module.
  2. Accept commands as SMS messages from a GSM module.
  3. Send position info back as SMS.
  4. Continuously send position info to a webserver.

Design considerations

And my initial design considerations (aka “keep this in mind when designing the thing”) are:

Power

Everything must be run off a 3.7 V LiPo battery. So think about power consumption and battery capacity.
The LiPo will be charged with a mini-USB cable.

Enclosure

Think about the size and mounting of GPS and GSM modules as well as antennas for GPS/GSM.
We’ll also need access to a USB socket for charging.
Also, the LiPo battery needs to fit in the enclosure.

I’m thinking either laser-cut acrylic case from Ponoko or 3D printed box from Shapeways

Components

The components I have in mind for this project right now is:

  • MCU: NXP LPC11U24 ARM processor. I’m thinking that is a good project to start switching from AVR to ARM.
  • GPS: SUP500F GPS module since that’s what I already have in my parts box. Otherwise I would probably choose a more modern module.
  • GSM: Telit GE865 on breakout board – again the reason is mainly that this is what I already have. But it’s still nice.
  • LiPo charging IC: The Microchip MCP73831 looks like it fits my purposes perfectly: it is designed to charge one LiPo cell from a USB port and it has bi-directional status output.
  • Status LEDs: a couple of 0805 or 1210 SMD LEDs. The exact model is not critical.
  • SIM holder: a generic SMD SIM holder. Something like this.
  • Battery: 1000 or 2000 mAh 1s LiPo battery. This one for example.

Next steps

The next step is, of course, cobbling together a prototype. And in order to do that, I will:

  • Get the GSM module working: find a suitable SIM, figure out how to send and receive SMS'es and get HTTP GET and PUT working using GPRS.
  • Verify that the GPS module works.
  • Create block diagrams for hardware and firmaware (i.e. identifying components and dependencies)

Stay tuned…

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