SDG #09 Trimble SVeeSix GPS Receiver

The Trimble SVeeSix is an older OEM GPS receiver module, the kind of board that appears cheaply on the surplus market and looks tempting until it becomes clear that it does not simply plug into a USB port and start producing NMEA sentences. This project works through what it actually takes to get one communicating.

The hardware tour covers the module’s construction: the GPS front end, the Trimble ASIC and microcontroller handling correlation and position solving, the memory and backup arrangement that preserves almanac data between power cycles, and the connector pinout that catches most people out. Because the serial interface is RS-422 rather than plain TTL or RS-232, a level conversion stage is needed, so a small adaptor is built to bridge RS-422 differential signalling to standard RS-232 for a PC serial connection.

With power applied and an active GPS antenna attached, communication is established using Trimble’s TSIP binary protocol through Trimble GPS Studio. That software makes the difference between a mystery board and a usable receiver, showing satellite tracking, signal levels and position fix data once the receiver has acquired enough satellites for a solution.

The practical conclusion for anyone considering surplus GPS modules is to check the electrical interface and protocol before buying. A TSIP only, RS-422 receiver like the SVeeSix demands an adaptor and vendor specific software, whereas a modern low cost module gives NMEA output over TTL serial immediately. The SVeeSix is a rewarding subject and a good lesson in serial standards, but not the fastest route to a working GPS project.