See the XoomBox in our shop GPS Receiver

Tuesday, 24 July 2012

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GPS Receiver

The standard XoomBox features a mini-din connector on the front panel intended for use with a serial GPS receiver.  Many of these devices are available cheaply and they provide position information in a standard (NMEA) format which can be added to the data logs.

The biggest problem with using NMEA devices over a serial link is that the data rate is limited to 1Hz updates.  There are a no. of proprietary solutions available to extend this, but it's difficult if not impossible for us to produce firmware variants to support such devices.

Instead we chose to implement our own high speed GPS receiver, located internally in the XoomBox case,  with an external active antenna to give the best possible satellite reception and at the same time increase the fix frequency to 5Hz.

The resulting board is shown in the photos below.  Also included are a couple of screen captures showing the GPS data in Google Maps.  The pictures show raw 1Hz data from a serial GPS receiver and also raw data from our internal 5Hz board.  The final picture shows the 1Hz data interpolated up to 25Hz by XoomCentre.  The resulting track diagram looks very smooth but is only an estimate of the path the car actually followed.

Click on any of the photos to see it full size.

The standard XoomBox V2 layout

The 2 small boards at the top of the picture are the SD memory card holder on the left, and a battery powered clock calendar on the right. These are replaced by the new GPS board

XoomBox with new GPS board fitted

The new board is visible at the top of the picture, replacing the original 2 smaller boards.

GPS antennna connection

At the top tight of the fron panel, a new hole has been drilled for the GPS active antenna connector

1Hz raw data

GPS data recorded by an external NMEA receiver at 1Hz update. The raw data is overlayed on a Google Maps display of the track

5Hz raw data

The same corner, but this time the GPS data came from our internal 5Hz GPS receiver

1Hz interpolated

This is the 1Hz data from the earlier photograph after being interpolated by the XoomCentre software. The sample rate has been increased to 25Hz to match the rest of the log channels. The resulting curve is smooth and realistic and a fair approximation of the path the car would have taken.

 

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