GPS tracking of vehicles revisited

Rob Brookes' Blog - MRMap and Communications Info

GPS tracking of vehicles revisited

Postby Rob_Brookes » Wed Apr 28, 2010 2:53 pm

The attachment to this posting titled "Details of how to add an external hand-held GPS receiver to your SRM9000 vehicle radio without needing any special accessory boards" "A9k-922_External_GPS_V_1_1.pdf" is available from the downloads section.

Another one that I'm starting to get questions on again, which would indicate no one reads these posts anyway. :cry:

How to track vehicles (by which they usually mean "Cheaply!")

There are three ways of adding GPS tracking to vehicles using Simoco radios that I know of, one of which I played with many years ago but couldn't afford to progress as it used a Dmap board. Dave Binks is currently looking at this method again so at some stage I'll pick his brains and write that one up for those interested.

That really only leaves two viable methods as far as I know.

The first is to use the MA-ASIGF accessory board which is similar to the board described in the last post. This time however it comes with a GPS engine fitted. Because it only has a single port, the fitting of a GPS engine to an ordinary MA-ASIG board renders it's external RJ45 port almost useless as the GPS now needs access to the internal connections of this port. That said, all you would really want to use the board for is to provide GPS tracking of your vehicle so it doesn't really matter.

Fitting the board yourself isn't rocket science as there's only a single ribbon cable connector to fit although this is as fiddly as it comes and it's easy to get it on the wrong pins. The ribbon cable as numerous wires, all coloured grey except one which is red. This red one lies alongside the RJ45 sockets if the cable has been fitted correctly. Using an MA-ASIGF board purely for GPS tracking means you don't need to remove either of the two knock-out covers as the underlying RJ45 socket is never going to be used.

Please (please!) don't be tempted to bring the GPS antenna cable out through one of these holes as the strain this puts on the connection to the GPS itself will soon have it pulled off. Drill a small hole in the plastic panel on whichever side you chose to have the GPS antenna connection mounted and fit the bulk-head SMA connector through it. There's a lock nut provided for this purpose. If you use the plastic end cover that has the knock-out panels over the RJ45 connectors then look at the back of this cover and you'll see two round indentations on the flat part of the cover. Drill through either of these and fit the SMA connector there.

Program the radio for 'ASI-GPS' and set up the callsign for that radio etc. That's it.

The second method, as described in the attached TMC publication, is for those team members who have SRM radios in their vehicles but can't justify the expense of a full MA-ASIGF board. SARDA handlers are the ones that spring immediately to mind but anyone with a Simoco SRM9000 radio can use this method.

All you need is a hand-held GPS receiver of the simplest kind but it should have a serial connection used for downloading tracks and waypoints etc onto a computer and not a USB one. Anything such as a Garmin eTrex or similar will do nicely. In fact anything back to and including the Garmin 12 type works fine. Add the necessary connections to the facility connector on the back of your SRM as per the TMC notes (2 wires). Program the SRM for 'External GPS' and away you go. The advantages of this method are that A....It's cheap as an old, simple GPS receiver can usually be found somewhere and B.... It gives the driver his or her own position as a British grid at the same time as telling base what it is. Secure the GPS onto the dash where it can see the sky and that's all there is to it. Your base will see you appear on MRMap in exactly the same way an MA-ASIGF system does. There's no practical difference between the two methods.

If anyone wants to try their hand at experimentation, you can buy magnetic mount GPS engines where the whole thing, antenna and GPS engine itself, is mounted in a small case that sticks to the roof of your vehicle. There's only a thin cable to enter the vehicle via one of the doors. These devices usually run from 5 volts and unfortunately the only voltage available from the radio is 13.4 or thereabouts and so some way of dropping the supply to 5 volts would be necessary. A bit more wiring is required for this method but anyone who feels themselves capable of handling it might want to give it a try. I have one of these wired up and it works well. As it's now powered by the radio vehicle supply rather than it's own batteries as an eTrex would be, it becomes more 'part of the radio' and can be left in place when not being used.
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