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Author Topic: Hooking up Touchpad from an old MP3 Player?  (Read 2787 times)
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I dissambled an old LG Media Player and would like to reuse its 3x3 touchpad.
As I'm still quite new to Arduino and interfacing with electronics in general, I'm not really sure how I can approach this.

The touchpad has a 10 pin ribbon cable with Ground and VCC marks (even though I'm not sure which of those tiny lines is what now).
I would be glad about any hint on how and if I can connect this without any extra hardware to my Arduino UNO.

Small resolution picture:


Full resolution picture:
http://i.imgur.com/ETWBC.jpg
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Sometimes the 'touchpad' on inexpensive MP3 players is actually a matrix keyboard with wires for rows and columns.  You might be able to see separations between rows and columns if you look carefully at the 'touchpad'.  Would a 5x5 or 4x6 matrix make sense with the user interface provided?
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Its hard to see if there is any seperation or not, atleast for me :/
The user interface on the other side has 9 buttons which corrspond to the Tx marks on the back.
The white frame you can see has some sort of sikicon blobs that are "connected" to small bumps on the PCB, I guess its measures the temperature to detect if the button is touched?

Also interesting to know that this is/could be considered a keyboard. Where exactly is the diffrence in the defintion of a keyboard and a touchpad? Does a "real" touchpad has to send x,y values instead of something like "button x" pressed?
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A matrix keyboard has switches that connect 'row' wires to 'column' wires.  The processor energizes one 'row' at a time and if one or more of the 'column' wires becomes energized it can conclude that the switches connecting the energized row to those columns have been closed.

A 'touchpad' is usually an analog device that produces voltage signals that indicate where on the surface the pad is being pressed.  A resistive touchpad usually has four connections: X-max, X-min, Y-max, Y-min.  The processor energizes them in pairs and measures the voltage on the other connections to determine where the pressure is.
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Interesting to know! Thanks!
I removed that grid thing and it actually looks more like those buttons are just photoresistors. The grid holds all the buttons which are nothing more than transparent plastic bits.
I couldn't explain it myself any diffrent than that the buttons react to light as I somehow doubt these things measure heat?

I guess you are right about the keyboad thing but I'm still not sure how that would be connected to an arduino :/

New picture:
http://i.imgur.com/Jdw6U.jpg
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Check out the chip data sheet product.ic114.com/PDF/S/SS01.pdf

As the text says its an
8-CH Digital Capacitive Sensor

That's why there are 2, bit of a waste, could have lots more buttons.
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Thanks! That actually helps
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The other thing I wanted to mentions is, could the top and bottom PCBs have been connected via the open pads around the edge, that way you would have GND over the pads, power on 1 pin and the 9 signals, other wise it must be multiplexed some how, and it wasn't clear from my quick look at the sheet about that.

good luck getting it working, its should be possible, try and trace out the PCB, or at least the key bits where it set up the operating mode via the 2 OP pins. I did try to see it in your image but its out of focus.

... Simon
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I'll try to make a sharp photo like the other one without the grid later.
What I just discovered, while removing the grid its seems that I broke one of the connections to the ribbon cable.
The very last on the bottom. You can even see on the blurry picutre. What is this black pin that most connections have and is it some sort of resistor or could I just remove it and repair the connection with some normal solder?
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What exactly did you mean by "black pin that most connections have"? It looks like a regular Molex cable. these things are very hard to repair. The best thing to do is get an 80-conductor cable from a hard drive. The 80-conductor was used to help cut down on cross-talk and noise. They are small enough to replace the Molex cable and they are also single strand copper wire. Cut the hard drive cable to the length you need and peel of the number of wires you need. They don't need to be individual unless you want them to be. With a low wattage soldering iron (15-20 watt) heat the Molex cable and gently peel it away from the circuit board. After the cable is completely removed; clean the solder pads with desoldering braid. This will leave the pads bright and shiny and leave just a little solder on the pads to make the new wires stick better and more easily. Strip about 2mm of the insulation off of the end and put very small amount of rosin on the wire and then put a little solder on the wires. The rosin makes the wire heat up faster and the solder to melt faster and adhere to the wire. It only takes a second for each wire so take your time. When all the wires are done, touch them to the pads on the "keyboard" very lightly with the soldering iron (also just a second for each one). And try not to get the wires too close to each other. The other end of the new cable can be connected with the hard drive connector (just be sure to know which wire is on which pin using an ohm meter).
A picture of the other side of the touch pad would be good also.
Hope this helps.
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I meant the connectors before the flat ribbon cable. There are these tiny small bridges just before the cable and they have this tiny black thing that connects the two soldering points. One of these are broken.
Thanks for the tip with the cable though!
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the little black things are resistors. you'll need a good magnifying glass or jewelers loop to see what the numbers are/were. hopefully they were right at the breakage but they probably were and are now unreadable. the next thing to do is see what pin of the decoder chip the broken resistor went to. if it was a data line (for the columns or rows) then read a resistor from another of the same type of line (column for column, row for row) and replace it with a resistor with that same number. In this case, close won't be good enough. it has to be exact.
if you don't have a resistor then try a computer repair shop. they sometimes throw out bad mother boards and I use those boards all the time for scavenging for parts. especially the header pins.
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Not to be an old grumpy man, but really, if you don'e even know what SMD resistors are called, you are better off starting with leaded components and learning a bit about electronics before starting on such a complex project.

// Per.
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