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Schematic for a capacitive keyboard

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luben111

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Hello,

Does somebody have working scheme for capacitive keyboard?

I have to make 4 keys on flat panel. Currently I use flat keyboard, but I have to make them without any movement parts.

I had one old scheme with 7474 that detects the delay of the plate, when somebody touches, but it's not very sensitive.

The plate of capacitors should be covered with 0.2 mm thin polycarbonate.

Regards
Luben
 

silvio

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designing a capacitive keyboard

Hi Luben,

Learn to do it professional, not only for immediate needs. Almost every data sheet reveals some hints about how to design a capacitive sensor.
These ICs will create sense fields through dielectric surfaces such as plastic or glass up to 100mm (4") thick, and can even turn small objects into sensors. These sense fields can work easily through gloved hands.
If you think you can do it reliable without using some well proved solution in wild environment, feel free to try. But for $2.89 single quantity it worths to give it a try. I know, I know, shipping charging, finding nearest distributor, not so easy to achieve.

http://www.qprox.com/downloads/d/qt140_150_100_datasheet.pdf for a quick look

Then you can start digging from here: http://www.qprox.com/products/touch.php for all product range.

I know it's not common solution, but someday you must start designing professional, fast, reliable and less headache. Unless you'll develop your own capacitive sensor, use other works.

Regards,
Silvio
 

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