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This question already has an answer here:

How cooktop buttons works? In this picture can see circles (marks) from control board. cooktop glass from inside

Here are control board with buttons. If i touch that black "buttons", it is like dish wash sponge. Control board (part one)

How that buttons works ? Because in glass have no holes or some wires. Those black "buttons" are some special material?

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marked as duplicate by Anindo Ghosh, PeterJ, placeholder, Dave Tweed, Matt Young Jul 18 '13 at 11:20

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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Those black "buttons" are conductive foam, extending a touch sensor's conductive surface to just below the inner surface of the glass.

This allows capacitive touch or capacitive proximity sensors on the PCB, under the conductive foam, to sense touch / finger proximity on the upper side of the glass.

See this answer for some possible touch / proximity sense components, and a description of how they would work through glass.

QTouch

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