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I'm a beginner in electronics, and I'm ignorant of many basic things.

Check out these black things on the board:

enter image description here

These are from a keyboard.

I'm disassembling it and I want to connect my own switches to it. All the connections seem to go to these black things. But I have no idea how to connect to them. How can I do that?

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    \$\begingroup\$ @Andyaka - I'm pretty sure he means the gray/black rectangles in a line on the board.. \$\endgroup\$ – Connor Wolf May 18 '13 at 10:50
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    \$\begingroup\$ @Andyaka - They don't look gold to me at all. Plus, they're noticeably convex, and that much gold would be ridiculously expensive. They also have a clear texture. \$\endgroup\$ – Connor Wolf May 18 '13 at 10:58
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    \$\begingroup\$ Those pads are nothing to do with any actual capacitive keyboard functionality, whether the keyboard is capacitive sensing or not. Those are contact pads, usually a conductive elastomer, used for making contact with the PCB traces seen on the transparent flexible printed circuit. This is similar to the elastomer strips used for connecting to LCD panels. \$\endgroup\$ – Anindo Ghosh May 18 '13 at 11:12
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    \$\begingroup\$ @Andyaka They look black on my color-calibrated monitor, anyways. \$\endgroup\$ – Connor Wolf May 18 '13 at 11:15
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    \$\begingroup\$ @Andyaka they don't look remotely the same color as the vias... Unless maybe your going color blind pal. \$\endgroup\$ – Passerby May 18 '13 at 17:15
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Those black sections are either a carbon-glue paste, or a conductive, carbon-doped elastomer. The carbon makes them (somewhat) conductive, and the rest holds it together. They then make contact by simply pressing against the silver-laden ink traces of the keyboard (in the background of your picture, I would guess).

If you want to connect to them, you're probably going to have to scrape the black paste off the contacts, until you reach bare copper, which you can then solder to.


Are you sure that is a capacitive keyboard? The keyboard membrane in the background looks like a pretty standard pressure-activated membrane switch assembly to me.

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  • \$\begingroup\$ I'm not sure whether it's capacitive or not. Here's a picture: i.imgur.com/jQ3T3Xr.jpg Can you tell me whether it's capacitive or something else? \$\endgroup\$ – Ram Rachum May 18 '13 at 11:38
  • \$\begingroup\$ If you want the keyboard to remain functional, it may be easier to use a separate MakeyMakey \$\endgroup\$ – RedGrittyBrick May 18 '13 at 11:54
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    \$\begingroup\$ @RamRachum That flexible white rubber sheet definitely means its not a capacitive keyboard. \$\endgroup\$ – Passerby May 18 '13 at 17:16
  • \$\begingroup\$ @ConnorWolf The way it was originally connected to the contacts on the sheet is that there's a metal bar, not shown in the picture, pressing them together and not allowing either to move. Could I get something similar, except instead of the contacts going to a sheet, they'll go to wires that I can then connect to my own buttons? \$\endgroup\$ – Ram Rachum May 23 '13 at 14:26
  • \$\begingroup\$ You should be able to take a piece of perfboard and run some wire in the same pattern/spacing as the contacts and solder to that. Alternately, could you just put a piece of tape over the contacts, lay your wires on top of that, then reassemble it using the bar to hold everything together? It's pretty low-budget but it might work to get you started. \$\endgroup\$ – TMN May 23 '13 at 20:52
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Easier than scraping away the black stuff may be to follow a copper trace from the black pad to a nearby via, and solder to the via. Or take it further and follow the via through the board, where another trace may take you to a larger copper pad that's easier to solder onto.

To solder onto a via, you'll need pretty thin wire, say 30 gauge solid (not stranded) wire, maybe even smaller, 36 gauge if you can find it. Such thin wire and small solder connection will be mechanically fragile, and will snap off easily, possibly tearing away the surface copper from the via. Be sure you have some mechanical strain relief or way to prevent the wire from moving & bending near the solder point, like glue the wire down to the board an inch away from the solder point.

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