Design experience with rubber switches?

Do you need rubber? We use pcb mount mechanical pushbuttons, Panasonic and Omron, in the 15-19 cent range in fairly small quantities. They have a nice snappy feel.

John

Nice product blurb, but how about a link to the switches?

Thanks, Rich

Oh. Yes. That.

Try Panasonic EVQ-PAC04M sort of stuff, and Omron B3F-1052 ishness.

Also see disgusting relay watchdog circuits in a.b.s.e.

John

Hello John,

Nice system that you've built there.

I had looked at all those kinds. Up and down Digikey, Mouser, Newark, Arrow and so on. The problem is that they are only about 3.5mm in push surface diameter. I have to keep the button surface flush with the front cover, or rather a tad recessed to deal with tolerances. This in order to prevent accidental turn-on of the unit when someone lays it down on the face, tosses a newspaper on top or carries it in a messy briefcase. The messiness factor of an average briefcase can be quite extreme :-)

The Cannon is 9.5mm diameter so an average finger tip can press it into a hole without breaking a nail. I really need something wide and round. Now if women would finally give up on those ugly glued-on nails this design task would be a lot easier.

Regards, Joerg

How about the stuff they use for the front panels of microwave ovens? They're zero depth, and big enough for a finger or two. ;-)

Oh, but wait - you don't want them to get accidentally pressed when the customer tosses the unit into their gym bag.

What to do, what to do....

How big is the front panel? How about a .032" Al sheet, with a .375" (or so) hole over each "button"? And spec the domes on the topsheet for "hard-press"? ;-) Ya got a trade-off between "easy to press on purpose" and "hard to press accidentally, no?" :-)

Good Luck! Rich

Hello Rich,

It is too expensive :-(

It's going to be an ABS case, no domes although in the long run we could do that. Initially it needs to work with a regular flat off-the-shelf thingie. The rubber buttons might work if we can find an ABS case with a thick enough front so the button can't be pressed 'under'. That's why I asked whether anyone has experience with these. However, the fact that none of the Digikey type businesses carries them does not create a warm and fuzzy.

Regards, Joerg

I've had a little experience.

You can make up your own pattern to be honest.

Try googling 'elastomeric switch' and 'membrane switch' for more suppliers.

Graham

Hello Graham,

With the ITT Cannon switches or similar ones?

This is the first series where I saw that being done by just cutting away switches. Anything else was full custom mold making and the whoile nine yeards, high up front NRE costs.

I had tried that. Membrane switches are usually the flat polyester film layers, not very suitable for a single push button. Elastomeric yields other companies but typically smaller custom outfitters. The Cannon is, so far, the only one that I have seen coming standardized off-the-shelf from a major manufacturer. I was a bit surprised that Omron or Panasonic don't make them.

Regards, Joerg

Well, look at the front panel of your microwave. Or, for that matter, inside a keyboard:

That'd give you your flat switch array, and then just put whatever size holes you want in your front panel.

Have Fun! Rich

Hello Rich,

I know, I just had to take mine apart for cleaning. Washed all the layers and carefully dried them near the wood stove. Now all the keys work again.

You can't easily get this for a one-button situation. Also, look at the number of parts: Two silver trace layers, one membrane spacer layer, a rubber post plus a cap. I'd rather have a one-piece solution instead of five parts.

Regards, Joerg

Eh ?

What's all this about layers ?

The switch contact fingers are formed by traces on the pcb and the switch ( the contact pill ) sits above it. That's all.

Try taking a TV remote apart. The traces in the switch area will be carbon coated ( cheaper than gold ).

Graham

And a lot less reliable.

Stop and think how often a TV remote button gets pressed !

Graham

Hello Graham,

Well, that's what the Rich's link was describing. It's how most lower cost PC keyboards work or at least used to work.

That's exactly how the ITT Cannon rubber switches work. I just wanted to know whether someone had used them and whether the experience was on the positive side.

Regards, Joerg

Not yet, but heading down this path. I've dissected a mass-market product (a flashing toy ring) that uses a similar but smaller single switchpad. I can share how they implemented it, FWIW...

For a button 10.5mm square with a 5mm round top and a 4mm carbon contact pad, they laid out a set of 12/12 tinned (?) finger traces 4.5mm long (2 fingers on one net, 3 on the other).

What I can't speak to is longevity of the traces or the contact pad. So far, oxidation on the traces isn't an issue.

Richard

Hello Richard,

I have seen the 2/3 comb pattern on a remote. Another used 1/2 comb and failed quite early on. Yet another had them meandered and this also failed. But these failures could be related to the carbon content rubbing off.

Tinned? Yuck. That doesn't seem right. Ideally it should be gold plated but that probably wasn't in the cards. Tinning can lead to problems with residue like rubbed off post material, dust, Cheerio crumbs, pretzel parts and so on lodging in between.

Depends on how long you have that toy ring and where it's usually stored. I found that even the difference between the garage and inside the house is very noticeable.

If you know other sources beside ITT Cannon please let us all know. I am pretty sure we won't be the only ones for too long who need this stuff.

Regards, Joerg

Yep. This is new turf, so I haven't explored alternatives to gold plating yet. At the moment, I'm just looking to get a prototype working with similar parts (e.g., packaged IC instead of die), expecting that it'll be re-designed by those more knowledgable in commodity products before it goes to production, if ever. I doubt gold will make the BOM in the final product due to cost.

Actually, looking closer, it looks like the whole PCB is plated with a silvery material under the mask; there's no HASL. Whatever it is, it's very cheap, as you'd expect of a toy - every part of it has clearly been optimized for cost (down to the commodity mini-LEDs with u-bent leads so they could use a single-sided PCB).

Hadn't gotten that far yet. Frankly, I was planning to scavenge the part for the protos and let the re-design guys worry about the source. The ITT ones are bigger than I need, but may be a workable option too. I'll let you know if I come across any others.

Cheers, Richard

Hello Richard,

Gold or nickel are pretty standard these days but not in very low cost gear because it is an extra production step. Probably the PCB in your toy model isn't even FR4 but phenolic. Believe it or not, even large TV sets often have a phenolic main board to squish the last 10c in cost out of them.

That would be nice.

Regards, Joerg