Android Enternal Power Switch.

Android Tablet Power Sequence

If the Android is to be embedded in a stand-alone manner, there must be a method of automatically monitoring the power input, turning the device on and booting up into an application.  This page describes how to add a jumper to the power on/off so that some external monitor/controller can  apply the power ON sequence and the power OFF as needed.  The power on sequence in most android devices is Hold the Power Switch Down briefly and the power on/boot sequence begins.  Power Down is slightly more complicated.  Hold the power button down while the unit is on and shortly a “Power Down” question will appear.  The saving grace is that if the “Power Down”  is  pressed longer for perhaps 10 seconds, the unit will bypass the question and power off when the button is released.  The power switch in the Android (or at least the ZT-180 tablet) is reasonably accessible and the contacts can be extended via a small cable so that an external controller can supply a simulated power ON button press or a simulated long power OFF button press.

Materials Needed

A. Small tip Phillips screwdriver.
B. Paperclip or a very small blade Jewelers Screwdriver for pressing on  slides.
C. 15 watt soldering iron.
D. Small amount of 1/32″ rosin core solder.
E. About 18″ two conductor of 24 awg zip wire or finer wire.
F. Wire cutter and stripper.
G. Electrical or masking tape for insulation.
H. Ohm meter.

Opening the Tablet.

Please Note: I’m sure opening the tablet and soldering a power switch jumper wire voids any warranty you might have at all levels. 

There are two small openings on the left side end of the tablet.  They may be under  small labels.  They may be a small hole about paper clip size or they may allow a small screw driver tip to be inserted.  The small  openings allow access to the two slides that hold the unit in the case.  If you press down with a paper clip on the end of the slides they will slide down a short distance and you can gently lift the unit out of the rear case.  Once you have done this disconnect the battery before going any farther.

Freeing The Motherboard

There are about five small screws that secure the motherboard.  Remove these and then free the small ribbon cable from its connector.  Gently turn the motherboard over and locate the push button power switch where you will solder the jumper.

 

 

 

Adding the Jumper Cable.

A. Preheat the soldering iron.
B. Prepare the wire by splitting the cable on both ends and then strip the insulation back approx 1/8 “.
C. Tin the wire ends that are to be soldered to the power switch. 
D. Add a small amount of tape to the components near the power switch for insulation
E.  Solder one wire end to one of the power connectors and solder the other the the remaining power connector.
F. Connect the ohmmeter to the other ends of the connector wire.  There should not be any reading until the power switch is pressed.  If there is a reading, inspect for a solder short.  Press the power button.  The ohmmeter should indicate a complete circuit.

 

 

 

Getting The Extension Cable Outside.

Before reassembling the tablet,  you should consider how the cable should  be routed outside.  I chose to drill a small 5/32″ 4mm hole  in the back case.  See figure.

 

Reassemble Tablet And Test.

Carefully reverse the dis-assembly process, by reattaching the motherboard,  reconnecting the small ribbon cable, and lastly reconnecting the battery.  Test the new power cable by briefly touching the ends together.  The android should power on and boot up in the usual manner.  Once the unit has power up, test the power down sequence by touching the external power cable’s ends together for about ten seconds.  The screen should display the “power down” question and go blank when the two ends are released. Route the cable outside and re-assemble the front and rear case.

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