Mobile GPS - Hardware

The Mobile GPS project is a small circuit board that adapts a Motorola M12/M12+/M12M GPS engine for use in an automotive application.  The design includes reverse polarity protection, transient protection, and extended temperature operation.



Mobile GPS Top View.

Mobile GPS Bottom View.

Theory of Operation

DC power in the range 7 to 20 volts is provided on terminal block.  Diode D1 provide reverse polarity protection.  The LM2672 switching regulator provides buck regulation down to 3.0 VDC using a high efficiency 260KHz switching frequency and small inductors.  R1 and R6 set the output voltage.  C6 filters the output.  Additional ripple reduction is provided by the 4.7uH inductor and C1.  LED1 provide a power on indication.  IC2 is a standard 3VDC ST-3232 driver that provides translation between GPS 3.0 VDC data signals and the +/- 12 VDC RS-232C standard.

Although the Motorola GPS M12+ includes an optional internal battery to store the GPS almanac and ephemeris data, an external battery was utilized in this application.  Since the GPS engine is mounted in the vehicles' trunk and subject to the extreme Arizona summer temperatures an external battery provides extended operation.


Power Converter Schematic / PCB Layout

For best quality, print the schematic on a single 8½ x 11" sheet of paper in landscape mode using your favorite graphics application.

Schematic (Graphic - GIF)	PCB Layout Top Layer (Adobe PDF)	PCB Layout Bottom Layer (Adobe PDF)

Additional information on viewing the PCB artwork, PCB tools, and component libraries is available in the Technology section.