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Project logs / Re: Internal GPS for Tablet PC
Module fitted inside Tablet
Sitting in my shack was a less than pristine Xplore tablet PC.
In good condition these are pretty useful machines, rugged and fairly waterproof, with switchable dual mode touchscreen (resistive or active) and a few custom programmable buttons on the case. Mine was missing most of the case screws, the wifi antenna housings, and has a small LCD 'bleed' along one side of the screen.
I thought it would still make a decent nav system for my off road vehicle, but it lacked the custom Xplore GPS module to make it properly useful. No external serial port is fitted, and only one USB port. I dont like using USB ports for this application, the plugs are large and vulnerable to vibration and knocks, and Windows can get pretty upset if serial ports keep disappearing and reappearing. Stopping every few minuted to reboot the PC is no fun.
Peering inside the unit, I found two useful things...
1) a small board mounted to one side of the main board, which appears to do some switching of the wireless antennas (which my unit doesn't posess)
2) the custom external connections (for custom modules such as GPS) are connected internally by typical 0.05" pitch headers and cables.
Connection from motherboard to external connector
A bit of investigation and trial-and-error showed that the external harness connection includes everything necessary for a USB port (5V, GND and two data pins).
So I designed a replacement PCB, carrying a high performance u-blox GPS module, 3v3 regulator and associated gubbins.
New board compared to original part
The antenna connection is via a case mounted SMA connector since I prefer an external antenna for best performance, though it would have been simple enough to mount an antenna module on the case itself.
Since I'd have 10 PCBs made (Itead studio), and only needed one, I brought out the ublox serial and I2C connections to terminals for later experimentation, and doubled the USB connection to a Mini-B connector. This makes the remaining boards much more useful for future projects.
Everything worked nicely, the only change I'd make would be to replace the backup battery by a small supercap and diode. It's not necessary to have a battery fitted, but makes acquisition faster in some cases. I calculate the CR1220 primary battery that I designed in has around a 3 month lifetime.
Wiring harness routed around area where case heatsink is screwed down
Several of these have been built up (using first the u-blox 5 and later u-blox 6 modules) and performance is extremly good. It will often achieve satellite lock indoors, using a short piece of solder poked into the SMA connector as an antenna. Even with no backup battery fitted, the GPS has usually found lock before Windows and the Nav software have finished booting.
A nice simple project, which made an otherwise tired tablet into a useful piece of kit, with the added benefit that when things go wrong off-road, at least it wasn't in perfect condition to start with.[/quote]
I was in the market for a Tablet PC either Android or Apple doesn't matter much to me, and I was just wondering which ones out there that are reasonably priced and can be used like a GPS unit but offline. I don't want a 3G unit or something that requires a internet connection. Does any one own or know which tablets will do this? Thanks!