Question on Pushbutton terminology

May 02, 2004 3 Replies
M

What is a TACTILE pushbutton switch, compared with a MOMENTARY pushbutton switch?



I am pretty sure momentary pushbutton switch is your typical pushbutton that is normally open, and closes as long as you have the button pressed, and opens when you release it. What then is a "tactile" switch?



And i've seen pushbutton switches with a "ground" leg, usually a fifth leg, which is connected to ground (or chassis ground). Is that extra ground leg, usually used to protect against ESD from someone's finger? I really haven't seen a good use for that extra ground leg, since i haven't really heard of anyone frying their circuit due to ESD discharge thru a pushbutton from someone's finger.



Mike


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G

Same as a momentary pushbutton switch, except that you have to apply more force to make it go down than you have to apply to keep it down. Very popular feature with computer keyboards, going back to the IBM PC "Buckling spring" design. Also known as "snap action momentary contact."

Yes.

It happens, and it's something that a good engineer designs against.

Guy Macon, Electronics Engineer & Project Manager for hire. Remember Doc Brown from the _Back to the Future_ movies? Do you have an "impossible" engineering project that only someone like Doc Brown can solve? My resume is at http://www.guymacon.com/
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G

They're orthogonal concepts.

Tactile means you can feel it "click" when the contacts close.

Momentary means the switch is only closed while you hold the button down (as opposed to push-on/push-off).

(I've assumed a normally open switch. Adjust terms and required.)

Grant Edwards grante Yow! World War Three can at be averted by adherence visi.com to a strictly enforced dress code!
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J

When I worked with high-volume keyboards, the mechanical characteristics of switches were described by the force-displacement graph, which showed the force necessary to depress the switch at a given distance from its rest position. In a simple, non-tactile switch, the graph is more or less a straight line, with the force proportional to the displacement. In contrast, a tactile switch's f-d graph has a short center section where the force decreases sharply with an increase in displacement. Ideally, this is also where the switch changes state electrically (closes if normally open, or vice-versa). In some keyboards, the tactile effect is simulated by with an audible clicking sound when the key is depressed. For many people this produces a surprisingly good illusion of tactile key switches.

-- Jim McGinnis

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