Thursday 27 February 2014

pcb - How does this button work without any circuit closing device?


This may be a stupid question, but I have searched online for a little bit and can't seem to find my answer. I am working on a circuit board that uses buttons that i've never seen before. These buttons just have a metal lead around them and an LED in the middle (for lighting up the button I'd assume) but how does a button like this even work? I've attached some pictures to show you what i mean. enter image description here


this is the back of the push buttons from the device


enter image description here enter image description here



Answer



The gold plated interlocking concentric "rings" are two contacts of a switch.
When they are electrically connected by a resistance of less than say 10 k Ohms the circuit is activated.


The white "rubber" has a conductive ring on it which is close to but not touching the gold contacts - it is probably held clear by small protrusions in the rubber moudling. When the rubber is pressed from above it presses the ring onto both contacts and closes the circuit.


The conductive material is often made of a conductive ink or similar which may be loaded with carbon particles to make it conductive.



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