Laptop keyboard - how does it work?

[DaveC]

Underlying the key mechanisms is a double-sided film with concentric circuit
pads (for each key) on either side of the film. The key cap pushes down a
little inverted cone of what looks like silicone rubber to touch the film.

This isn't a contact switch; the top of the film has just one pad, as does
the bottom of the film; no electrical connection is being made.

Is this hall effect? I can't see anything on the end of the cone, unless
there's something impregnated in it.

The connector to the motherboard is a 40-pin flexible mylar cable.

What technology is used in this kind of keyboard? With 40-pins going
off-board, I presume all matrix processing is done on the motherboard?

Google didn't turn up any in-depth descriptions of keyboard technology.

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group

 

[Lord Garth]

"DaveC" <me@privacy.net> wrote in message
news:0001HW.BE7980C700090142F04075B0@news.sonic.net...

Underlying the key mechanisms is a double-sided film with concentric
circuit
pads (for each key) on either side of the film. The key cap pushes down a
little inverted cone of what looks like silicone rubber to touch the film.

This isn't a contact switch; the top of the film has just one pad, as does
the bottom of the film; no electrical connection is being made.

Is this hall effect? I can't see anything on the end of the cone, unless
there's something impregnated in it.

The connector to the motherboard is a 40-pin flexible mylar cable.

What technology is used in this kind of keyboard? With 40-pins going
off-board, I presume all matrix processing is done on the motherboard?

Google didn't turn up any in-depth descriptions of keyboard technology.

Dave, these are capacitance switches. Read here:

http://www.discovercircuits.com/C/capacitance-sw.htm

You can type by just touching the membrane lightly...