MP3 controller for Laptop or desktop PC

Question: So you have your laptop and it's impressive collection of MP3 files on it. You have spent 2K or more on a laptop however you can't cough up the additional 1K for an iPod. So.. what'chagonnado?
Easy: Outfit your laptop for about $50 and use it to play MP3s.
Level of difficulty: Medium - Involves precision soldering.

Tools needed:
1: Soldering Iron
2: Solder (duh)
3: Box cutter or similar cutting tool
4: Chainsaw
5: a six pack of your favorite drink

Materials needed:
1: a PS/2 or USB Keyboard
2: Project Enclosure Radio shack part no: 270-1804 and three packs of Mini SPST switches, RS part no: 275-1547
3: a spare piece of ribbon cable

In this project, we are faced with two obstacles, 1: How do we get the sound from the laptop into the car stereo and 2: how do we control the laptop without having to drive with the laptop open and without posing a driving risk?

Of the two tasks, #1 was the easiest. If you go to your local computer store or radio shack, look for an RF Transmitter. Or just tell them about this item. The iRock Wireless Music Adapter has two connectors, one coaxial power connector (for the included cigarette car adapter) and a 1/4 inch phono connector. The device will take any audio signal on that 1/4 phono connector and broadcast it to one of four frequencies listed on the side of the device. Now that we have #1 down easily, it's time for the harder part of the task of doom.

For this half of the project you will need a keyboard that you are willing to tear apart. You can use any kind of keyboard that you want. As long as it is capable of typing the letters that you need to work your player. I originally wanted to find a USB keyboard, however a PS2 keyboard was $5 cheaper.

Note: If you decide to use a USB keyboard, you might want to make sure that your OS recognizes it without prompting it for drivers. This way there's less mess if you want to plug it into other machines (like headless MP3 players).

What we are essentially doing here is taking a keyboard and trimming it down by 100 buttons or so by eliminating those keys that we don't need and leaving only those needed to run WinAMP or XMMS or your favorite player here.



The steps are as follows:

Start off by removing the keyboard backing. You will see a layout similar to this. In this view, you can see the three plastic sheets that make the keyboard as well as the control module hidden in the upper left corner. (it's under the horizontal bar).



Remove the control module and the plastic layers. Use the keyboard as a guide and circle the keys you are wanting to use. You can discard the back at this point. Here is a shot of the plastic sheets and the controller.

Keyboards are very simple in design. They are essentially an array of switches hooked up to a digital controller. The clear plastic pieces when layered form a switch array. When you hit a key, a connection is made between two contacts on that switch array. The digital controller picks up the connection via the card edge and translate it into the digital protocol and sends it to the PC via the interface cable. USB keyboards vary slightly only in the fact that they have a PS/2 to USB bridge, and quite possibly a USB hub as well.

All we need to do is to find out which pins to short to make the controller send the proper keys. This can be done by taking a sharpie pen and tracing the wire traces. In this example, we will be trying to find the traces for the keys listed below. At this point, you can find the pins for any key on the keyboard that you want to use. Since we are using Winamp/XMMS, we will use the standard keyboard keys:

PLEASE NOTE!!! The key pins listed below are only an example. Unless you bought the same generic black keyboard that I did from the store that I bought it from then you will want to check your pinout. Actually checking your pinout is a good idea anyways.
KeyWire traces
(top layer / bottom layer)		Winamp Function
Tab(20 / 1) Alt/Tab to restore window focus
Alt(15 / 22) see Alt
S( 2 / 21)Shuffle
R(4 / 19)Repeat
Z(1 / 23)Previous Track
X(2 / 23)Play/Restart Current Track
C(3 / 23)Pause
V(4 / 23)Stop
B(4 / 24)Next Track
Up(8 / 22)Volume Up
Dn(11 24)Volume Down


Figuring out which pins do what is the hardest part. Now comes the easy part. In order to make a good connection, you will need to check the pins on the controller. If they are black, or grey then you will need to take a boxcutter and scrape the connectors clean.

The next step is to take the piece of ribbon cable and attach it to the card-edge of the controller. Whn you are done, you should see something like this.

Once you have this done, you need to take a cut out of the keyboard. In this case, we want to be able to reattach the steel bar across the card edge connectors once we are done. This will help hold the wires on the card edge if the solder fails for any reason. Here is a pic of the keyboard piece that we have cut. This is a view of the controller mounted back to the plastic piece. Now would be a good time to check your soldering from the last step. Open notepad and short together the respective pairs and you should get the characters that you were looking for. If you don't get a certain character, check your soldering for an open solder joint. If you get two characters, see if your solder hasn't dripped onto another contact. If you get the wrong character altogether, make sure that you are shorting out the right wires and that you have the right contacts soldered.

You will need to remove every bit of plastic that is not necessary from where the controller was mounted. You will also need to design a layout for your keys. This is the pic of a few of the buttons being laid out as well as the controller position.

At this point, it is safe to mount all the switches and to solder jumper wires to the switches in order to form the switch array that we need to give us what we want. This is a view of all the soldering that is done, just needs to be tested and closed up.

The next step is to connect it to your PC and test it out. Make sure that all the keys work, as it will be harder to fix in the future after you close it up.

This is a view of the finished product.