Introduction: Turn a Cheap Samsung Galaxy S3 USB Dock to a Car/desk Trigging Media Dock

About: Studying to electrical engineer

Hi and welcome to my (Jr) instructable
Today I'm gonna show you how to turn a cheap $3 eBay Samsung Galaxy S3 (might work on Galaxy Note and S2 as well) usb dock to an expensive desk or car triggering USB dock with possibility to enable/disable those triggering modes.

What's the difference between docks?
Well there are a couple of different docks out there on the market. As far as I know there's 5 different kinds of docks; a car dock and desk dock, the two we are gonna focus on in this instructable which triggers car/desk mode. And then there's a media dock which is basically a desk or a car dock with a 3mm sound port for audio out that allows you to direct all sounds from your phone to through the sound port instead. And then there the mother off all super dock that enables desk mode, audio out, HDMI out and usb OTG at the same time which basically turns your phone into a computer with usb ports.
Part from these there's the fifth standard cheap usb dock you can order online which basically just acts like a stand for your phone with a usb connection. These docks are cheap and don't trigger anything and that's what we are gonna change.

But what's desk/car mode?
The Idea is that when you connect your phone into a dock it's suppose to recognize it and trigger a certain task. For advanced users this task can be changed to whatever the user wants by using different apps like eg tasker. But the default mode for desk dock is changing the lock screen to the night clock thus turning your phone to a table clock. Whilst in car mode, although not sure (cause I've never tried it since I don't have a car) I believe it triggers drive mode. Which I believe gives you bigger buttons and voice interaction with the phone (and same thing here, can be changed  and used to trigger other stuff if you know how).

for more info use google

Although this is a really easy hack some basic knowledge of electronics is highly recommended since you could potentially destroy your precious S3. This hack was actually made by my girlfriend and does not have 3.5mm audio output but I modded a dock  before this with audio out so i'll be covering that part too.

So... first off: I take NO responsibilities what so ever if you try this and you happen to ruin your phone, injure yourself, destroy something, burn something down, blow something up, get sick, tired, hungry, dumped... so on and so on... you get the point...

If you feel it's fair and still want to do this then let's go!

Step 1: What You'll Need

What you'll need is:
A soldering Iron, and some basic soldering skills
Resistors of different values
on/off switch/button
a Drill
a helping hand for the soldering
and some glue
shrink tube - optional
3.5mm audio jack - optional
and some wires

You'll only need the 3.5 mm if you want audio out on your dock and this you can either buy or scavenge from almost any old music player or mp3 player and use for this project.

The shrink tube, although not necessary it's recommended so that you don't risk shorting anything.

You'll also need somthing thin and hard to open up the case. (I used a knife)

Step 2: Let's Get Started

First thing you do is to open up your brand new dock to reveal the insides. Mine was not attached with any screws so all I needed to do was to find something thin to pray open the bottom part from the sides. (tip: use something softer than the dock plastic, like a hard guitar pick if you don't want to risk scratching it).
Once the top was removed the inside revealed a really simple usb extension circuit (basically just a usb cable from one end to another as shown in the pic) and some weight to make the dock a bit more sturdy. 

What you need to know are the different pins and their order in a micro USB connector
I've posted a description to that shows what the different pins are used for. the pins we are interested in are 4 and 5

if you want audio out you'll also need to find  pin 2 and 3.

the pins are as follows:
Pin 1: 5V
Pin 2: Data -
Pin 3: Data +
Pin 4: ID
Pin 5: Ground

The S3 phones will trigger different dock modes when they sense resistor of a particular value over the pin 4 and pin 5 (ground)
so you need to locate pins 1-5 in your circuit with a help from these pictures

for car mode the resistor value is 619k ohm and for desk mode it's 365k ohm (also apparently it's 1k ohm for S1 and either value for S2)

Step 3: Resistor

Since I made a desk triggered dock I needed to get the resistor value up to 365k ohm (that's 365 000 ohm) which didnt exist in any one resistor in my collection.
So I had to use three different resitors in series to get that value, or at least a value close enough to that.
in my case I had 330+15+22=367k which is just close enough to the 365 we were aiming for. Testing them showed between 362k-364k in the multimeter.

One leg is soldered to either pin 5 or 4 and the other one to the switch

Now the reason we want a switch between is because at first I soldered the resistor directly to pin 4 and 5, which worked and triggered desk mode. However it didn't respond to being connected to the computer which meant I lost data transfer ability. Since i wanted to use the dock both for file transfer and for desk clock I needed an easy way to turn on and off desk mode. And that's where the switch comes in.
However if you feel you're not gonna use your dock for any kind of computer communication then by all means solder both legs directly to the pins 4 and 5, put the dock together and you'll be done with your dock :)

For those of you who want data transfer, let's continue...

Step 4: Adding a Switch

This part is just as simple as adding the resistor
all you do is solder the other resistor leg to the switch and then connect the switch to whichever one of the pins 4 or 5 you didn't solder the resistor directly to to create a closed loop

When done use your multimeter to check so that there's no short between any of the pins especially pin 1 since a short there could potentially ruin your phone.
If safe, you can give it a try on the phone to see that it works

Now for those of you who wish to add a 3.5mm sound jack to your dock here are the extra steps for that:
But before we start there is a slight issue that i noticed with the 3.5mm audio out.
I wanted my dock connected to my computer both by usb and by 3.5mm sound. That way i could redirect sound from my phone to my computers sound card and use my computers sound system whenever I wanted by a few button clicks. But since the 3.5mm extension cable used between the pc and the dock also connects to ground it shorted the data pin 2 and 3. Which meant that I once again lost data transfer.
So the conclusion is that if you want data transfer, you can't have the 3.5mm cable connected to the same computer you want to connect to cause that will mess up the signals.

With that said...
The phone outputs sounds on the usb 2 and 3 pins
so for stereo sound connect left sound channel to pin 2(Data-) and the right channel to pin 3(Data+) and ground to pin 5(Ground)

The connections on the male 3.5 mm is that the tip is left middle right and the back is ground.
You'll have to figure out on your own how your 3.5mm jack is connected and where the connections go since it differs from jack to jack.

Step 5: The Finishing Touch

Now all that's left is to figure out where to place the switch and audio out if you added one and drill the necessary holes.

Assemble everything and enjoy your new improved dock!

If you did everything correct you should now be able to turn on and of either desk or car mode and play music and sound through the dock if you added audio out.

this instructable was made from the instructions in the forum link posted here under
for more info check out: