Design not to break electrical buttons

Question

Design not to break electrical buttons

Joshua Wales (Mechanical)

(OP)

23 Jul 19 19:04

Simple problem, if I have a large button a user can put their hand on then I'm afraid they can put too much force and break the electrical button underneath.

If I make the external button bottom out before the electrical button (push button switch) how do I ensure the electrical button always activates?

All the push button switches I've looked at either have a very small window where they are guaranteed to activate but haven't physically bottomed (limited over travel) out or no window at all (no over travel), you just have to bottom them out.

Am I worried for nothing? Should I just assume the push button switches are robust enough to handle the force?

This is a low cost consumer device application, and I'm trying to avoid adding extra mechanical complexity or big expensive switches.

3DDave (Aerospace) · Answer 1 · 2019-07-23 19:33:38

You need a switch/button combination with a high post actuation travel. In some installations it's done by using a switch actuated at right-angles to the button motion by a cam feature on the button. This way the displacement on the switch is limited by the cam and the displacement on the button can be as much as the designer likes.

The other way is to have a flexible lever on the button to limit the force on the switch. It's possible to make that lever zig-zag or loop around under the button to save room.

Cheap and robust aren't typically used to describe mechanical switches. Have you looked at capacitive sensors? The chips that work with those are cheap and I think some microcontroller chips have internal hardware to handle the task.

For example: https://www.instructables.com/id/Capacitive-Touch-...
http://www.ti.com/microcontrollers/msp430-ultra-lo...

Joshua Wales (Mechanical) · Answer 2 · 2019-07-23 19:56:00

Thanks!

I have considered doing a sort of linear camp profile to activate a microswitch or some other push button switch, so I may go ahead and do that, but definitely takes more room.

I'll do some thinking about a lever idea, I was hoping there was something I was missing here or some good off the shelf button options I hadn't found.

I have considered captive switches but there were some power consumption issues with those last time I evaluated it, but since the electrical design is changing I should take a look at that again.

I know keyboard gets way more cycles before breaking that I'd need for my application but then they don't use a mechanical switch persay mostly these days.

itsmoked (Electrical) · Answer 3 · 2019-07-24 06:28:13

This is already designed into push-button switches. Use them as you get them according to their data sheets. The data sheet assume mashed to the bottom always.

Keith Cress
kcress - http://www.flaminsystems.com

Joshua Wales (Mechanical) · Answer 4 · 2019-07-24 12:47:04

itsmoked, having looked at the data sheets though they don't generally give an allowable force then to know if they are designed to handle the specific application. Is there some general rule on how much force would be allowed?

Josh

itsmoked (Electrical) · Answer 5 · 2019-07-24 23:16:40

They generally give the minimum force required to actuate them. The most is what a human finger can impose on them. It's not hard for them to design a human limited stack-up as human fingers are only good for so much force and that very little plastic can handily deal with it.

Keith Cress
kcress - http://www.flaminsystems.com

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Design not to break electrical buttons