Notes on the S690 (similar to GPS440) GPS receiver unit

A page of the Stratford Stratford-upon-Avon and District Amateur Radio Society website

I bought a GPS unit for £10 at a radio rally from stall that had quite a few (email me for contact details) and I thought I'd share some of the info I have found about it to assist others who may also have sucummed. I was told they were from a large organisation who were upgrading all their vehicles and as they must have thousands there must be a lot of these units about. Although it said MDSI & S690 on the front the stallholder suggested I look up GPS440 on the web, this lead me to this Expansys page and it does seem to be a very similar unit.

The unit contains a main PCB which has a voltage regulator and RS232 interfacing circuits plus power (+12V) and 'D' type connectors and a ten way header socket into which is plugged the GPS receiver card/module. This module can be either a Trimble ACE series or a Motorola Oncore GT (Oncore info at TAPR) the latter being fitted in my S690. The spec on the Expansys page implies that the Motorola module has to be fitted for European (CE) EMC compliance so this version may be quite common over here.

The antenna connector, either a SMB or BNC (as on my S690) on the front is connected directly to this module by a flying lead. The antenna needs to be an active one (powered from 5V), I bought mine on e-bay for under a tenner but had to cut off the MCX plug to fit a BNC.

From now on I'll be referring to my findings with my S690 using the Motorola Oncore GT module so obviously some things won't be relavent to units using the Trimble module.


S690 front view without box	S690 inside with Oncore module fitted	S690 inside without Oncore module
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To get the unit working I set it up using Motorola's Windows application software called WinOncore12 (download it here) or do a websearch. Use the PC with RS232 plugged into the 9 pin 'D' type socket marked Port1 ('Host' on the GPS440), the RS232 lead needs RX & TX lines crossed. The Oncore GT can output GPS data either in Motorola binary format at 9600 baud or the more normal NEMA at 4800 baud, the chosen format is enabled from the 'Options' menu within WinOncore12. The default is binary, the unit may revert to this if the on-board rechargeable backup battery runs flat, it's something to beware of if expecting the GPS to drive your application such as a APRS tracker 'out of the box'. Note that to use the full facilities of Wincore12 with the GPS unit such as self-test or RX setup you need to be in binary mode. Only enable NEMA after you've done all such work. Even without an antenna the the GPS will output data and this should be obvious if you have the 'Command Monitor Window' open (in either mode).

I have traced the circuit of the main board of the S690 unit as best I can and present it here (below in a choice of formats). I have only shown what I believe is relevant for making use of the unit and can't give any gurantee as to it's correctness.


S690 schematic as Jpeg	S690 schematic as PDF (better quality)

I have recently modified my S690 to be able to power other devices (with 5V) such as my PDA. Rather than overload the existing 7805 regulator I added a 2nd one along with a DC outlet socket, see the below pictures.


S690 front panel showing 5V outlet	S690 inside showing added 7805 regulator
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For the future I am thinking of trying to fit an APRS tracker such as the TinyTrak3 inside. To get it in it may have to be the surface mount version but it would make APRS simpler with less wires in my car!

Clive,G0CHO

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