Garmin eTrex Auto-Power Up Mod

mod by Mike Manes, W5VSI
documentation by Larry Cerney, K�ANI

This modification allows the Garmin eTrex series GPS�s to power up as soon as 3 volts DC is applied. This modification is useful for applications where the GPS is embedded into some form of packaging or in a vehicle location that is inaccessible.

The modification only requires the installation of a small 10K ohm resistor on the display side of the PCB near the power button.

First remove the black rubber grip from around the eTrex and set it aside. Then using a small knife slit the double-sided tape that holds the grip on and the eTrex case closed.

With a small screwdriver carefully pry the case apart. There are no screws holding the case together.

With the case cracked open, unplug the cable that comes from the battery compartment and set aside that part of the case.

Carefully remove the GPS PCB. On the display side near where the power on button is you will see two solder pads marked ON1 and ON2.

It is between these two solder pads that you will very carefully install the 10K ohm resistor.

During �normal� operations ON1 has 3 volts DC on it and ON2 has -3 volts DC. The power on/off button is not a SPST (single pole/single throw) switch but a logic switch that causes the unit to power up or power down.

When 3 volts DC is applied the eTrex, the 3 volts flows from ON1 through the 10K ohm resistor providing the same logic level on ON2 that it would receive from pushing the power button. The eTrex can then still be turned off by pressing the power button or by removing the external power.