Glenn Baddeley - Garmin Cables and Power Supplies

• Introduction
• Cables
• Power Supplies
• Links

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Introduction

During 1998 and 1999 I constructed several cables and power supplies for my Garmin GPS38 receiver so that I could connect it to a serial port on an IBM-PC computer, and power it from various sources. Two female plugs to suit the Garmin data interface and external power socket were obtained from the Australian agent of the Pfranc network.

After some experimentation I settled on two cables:

• A short cable (3.2m or 10ft) to run from a GPS receiver to a nearby IBM-PC, where both could be in same location.
• A long cable (30m or 98ft) to run from a GPS receiver stationed at some particular point (eg. exposed on top of a large rock) to an IBM-PC positioned at a more convenient point (eg. under shelter).

A flexible power supply arrangement was devised which allowed the cables to be used with any of:

• A 6V battery (eg. a lead-acid rechargeable of 4AH capacity).
• A mains plug-pack (eg. for use where mains is available).
• The 12V supply in an automobile.

Here is a diagram showing the cabling options of the present set-up:

The following two sections present photographs and schematic diagrams of the cables and power supplies. I would appreciate any feedback or questions which you may have. Let me know if not enough information is provided or a technical description of the power supply is required.

The cables and power supplies should be suitable for the Garmin 12 (all variants), 38, 40, 45, 48, 89, 90, 92, II (all variants), III (all variants) and Street Pilot GPS receivers which use the same interface socket, although I take no responsibility for whatever you may devise or connect to your GPS receiver or IBM-PC.

Having fun with GPS,
Glenn

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Cables

The photographs and schematic diagrams are of two cables exactly as they were constructed. Of course, you can build your own versions with whatever cables and to whatever requirements you may have.

Short Cable

Long Cable

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Power Supplies

Here are the schematics and photographs of the three power supplies as constructed. There is considerable flexibility with both the circuit and construction options.

Schematic of power supplies

Battery Power Supply

Regulated Power Supply for Automobile

Parts List

2 x 1N4004 Silicon Power Diode 400V, 1A
1 x LM317T Positive DC Regulator IC
1 x 12 Ohm 0.5 Watt 5 % Carbon Resistor
1 x 1100 Ohm 0.25 Watt 1 % Metal Film Resistor
1 x 220 Ohm 0.25 Watt 1 % Metal Film Resistor
2 x 100 nanoFarad 50 V 10% Polyester Capacitor
1 x 2 pin DIN Female Socket
1 x 1.5 Amp fast blow 3AG fuse
1 x 3AG fuse holder
1 x Small tag strip for mounting circuit
1 x Small case

Regulated Power Supply for Plug-Pack

Parts List

2 x 1N4004 Silicon Power Diode 400V, 1A
1 x Green LED, 5 mm diameter, and mounting hardware
1 x LM317T Positive DC Regulator IC
1 x 12 Ohm 0.5 Watt 5 % Carbon Resistor
2 x 1100 Ohm 0.25 Watt 1 % Metal Film Resistor
1 x 220 Ohm 0.25 Watt 1 % Metal Film Resistor
2 x 100 nanoFarad 50 V 10% Polyester Capacitor
1 x 1000 microFarad 35 V Electrolytic Capacitor (option for AC Plug-Pack)
1 x 2 pin DIN Female Socket
1 x Small tag strip for mounting circuit
1 x Small plastic case with aluminium panel (83x53x28mm zippy box)
1 x DC Round Socket, 1.8mm pin

Plug-Pack

Any DC plug-pack in the range of 12 to 36 Volts, and 250 milliAmps rating or greater, may be used with the above regulated power supply.

Any AC plug-pack in the range of 8 to 28 Volts, and 250 milliAmps rating or greater, may also be used, provided that a 1000 microFarad 35 Volt electrolytic capacitor is connected as a reservoir. The positive terminal of the capacitor connects to the junction between the 1N4004 diode and the 12 Ohm resistor, and the negative terminal to the negative rail. A DC plug-pack may also be used with this modification in place.

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Links

• Larry's Home Page for his Garmin Connector is part of the Pfranc network, which has agents all around the world. The Australian agent is Brian Sommers.
• Waypoint+ Garmin Connection Information.

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