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How to Construct a Cable for Garmin GPS receivers
Thank you for obtaining a connector for Garmin GPS receivers from us. Connector Pinouts and Signals
This document will provide you with the information you need to construct
virtually any type of cable you may require, whether you want to connect Diagrams represent the view of the connector as
your GPS to a computer, two GPS units to each other, or to provide power seen from the side that plugs into the computer or
to your GPS. GPS. In other words, this is the side of the connec-
tor that you do NOT attach wires to. Keep this in
mind when constructing your cable.
Please remember that this information is provided without warranty of any
kind. Though every effort is being made to ensure that the information is
accurate, we cannot be held responsible for any errors or omissions. If DB-9
you construct a cable that doesn't work (or even worse, damages your 1 5 5 1
GPS, computer, or yourself) as a result of a mistake in these instructions, Male Female
we would appreciate learning about the error so that it can be fixed, but we 6 9 9 6
cannot be held liable for any damages. Pin 1 DCD Carrier Detect
Pin 2 RxD Receive Data
A note about supplying power to your GPS Pin 3 TxD Transmit Data
Some Garmin GPS receivers are capable of running off external power Pin 4 DTR Data Terminal Ready
ranging up to +32VDC or more, whereas others can only accept a maxi- Pin 5 GND Signal Ground
mum of +8VDC. If your receiver can only accept 8 volts and you connect Pin 7 RTS Ready to Send
it directly to a car battery, you will damage your GPS (sometimes 18 volts Pin 8 CTS Clear to Send
or more can be present at the terminals of a 12 volt car battery, depending
on its state of charge). If you want to build a cable providing power to such
a receiver, you must incorporate a voltage regulator circuit to bring the volt- DB-25
1 13
age down to an acceptable level (the schematic diagram for such a circuit
appears later in this document). Such a circuit isn't necessary if your re- Male
ceiver can deal directly with the voltage you are giving it. 14 25
13 1
We're aware that the GPS-12, GPS-38, and GPS-40 receivers are limited
to 8 volts, thus requiring a voltage regulator, and there may be others. Female
Garmin provides a centre plastic pin on the connector of their GPSes 25 14
which are limited to low input voltages. This enables a non-regulated pow- Pin 1 Shield EMI Shield
er supply cable to be constructed which cannot be accidentally used on Pin 2 TxD Transmit Data
such receivers. But the safest thing is to check your user manual before Pin 3 RxD Receive Data
supplying power to your GPS.
Pin 4 RTS Ready to Send
Pin 5 CTS Clear to Send
Assembling the Connector Pin 7 GND Signal Ground
The parts making up a Garmin-compatible GPS connector are shown in Pin 8 DCD Carrier Detect
the exploded view below: Pin 20 DTR Data Terminal Ready
Screw Cap Top Pins Base Plug
Mini Din-8
7
6 8
Male
3 4 5
1 2
Pin 1 HSKo Handshake Output
Note that the base section is oriented so that the side Pin 2 HSKi Handshake Input
with the larger centre hole is to the right. Pin 3 TxD- Transmit Data -
To assemble the connector, first insert the contact ends of the pins into the Pin 4 SG Signal Ground
side of the base with the small centre hole. Then place the top over the Pin 5 RxD- Receive Data -
pins so that it is flush with the base (the top and base together will hold the Pin 6 TxD+ Transmit Data +
pins securely in place). Solder wires to the ends of the appropriate pins Pin 7 GPi General purpose Input
protruding into the top piece, ensuring that you don't let the pins get too Pin 8 RxD+ Receive Data +
hot, or the plastic connector may melt. You can then place the cap over
the top and use the screw to hold everything together.
GPS Connector
2
If you are making an unregulated power supply cable, consider inserting Female
the plug into the large centre hole in the base (it's a friction fit). This will
help to ensure that the cable you make is not accidentally used with a low 3 1
voltage GPS receiver. If you're building a regulated circuit for a low volt-
age receiver that has a centre plastic pin, this plug must be left out. 4
1 Gnd Signal/Power Ground
For specific details on how to construct a cable, please refer to the "Con- 2 TxD Transmit Data
nector Pinouts and Signals" diagrams to the right, as well as the informa- 3 V+ Power
tion on the following page. 4 RxD Receive Data
Constructing a Data Cable for the IBM with a DB-9 GPS Mini DIN-8
Serial Connector Pin 4 (RxD) Pin 3 (TxD-)
First, determine whether or not you need a male or female Pin 2 (TxD) Pin 5 (RxD-)
DB-9 to plug into the serial port of your computer (most com- Pin 1 (Gnd) Pin 4 (Gnd)
puters will require a female DB-9). Use the pinout diagrams
on the preceding page for the DB-9 and GPS connectors, If your GPS emits a true RS-232 signal (most don't), tie Pin
and connect the following pins: 8 on the Mini DIN-8 to Pin 4 to ground it.
GPS DB-9 Incorporating a Power Source into your Cable
Pin 4 (RxD) Pin 3 (TxD) If your GPS is one of those capable of dealing with relatively
Pin 2 (TxD) Pin 2 (RxD) high voltages, all you have to do is connect the positive sup-
Pin 1 (Gnd) Pin 5 (Gnd) ply to Pin 3 (V+) on the GPS connector, and the ground to
Pin 1 (the same pin is used on Garmin receivers for both
power and signal ground).
Constructing a Data Cable for the IBM with a DB-
25 Serial Connector If you have a receiver limited to lower voltages, you'll have to
First, determine whether or not you need a male or female incorporate a regulator circuit into your cable if you want to
DB-25 to plug into the serial port of your computer. Use the use your GPS with anything like a car battery (via a lighter
pinout diagrams on the preceding page for the DB-25 and adapter, for example). In either case, don't forget to add a
GPS connectors, and connect the following pins: fuse inline with the external power source.
GPS DB-25 The following circuit will provide a steady output of 6VDC to
Pin 4 (RxD) Pin 2 (TxD) a GPS receiver, which should work for most Garmin models
Pin 2 (TxD) Pin 3 (RxD) (though as always, check with your manual to be sure of the
maximum voltage tolerated by your receiver, and double
Pin 1 (Gnd) Pin 7 (Gnd)
check the output voltage before connecting it up).
Constructing a Data Cable to connect two Garmin
GPS receivers
7806
Obtain two GPS connectors and wire them as follows:
in out
9-35V Pin 3 (V+)
GPS 1 GPS 2 + +
External 0.1