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I am toying around with some new mechanical design ideas. One thing I've never looked at it is the rubber keypads with the conductive "pucks" underneath. I've always used mechanical switches, or overmolded silicone buttons onto the finished enclosure for waterproofing.

Example of the conductive rubber keypads: http://www.rubber-keypad.com/Conductive-Keypad-pd6229345.html

I take it the manufacturer gives you a footprint that matches the conductive "puck", and the footprint goes to GND so when the puck hits, your logic line goes low.

Does anyone have any experience implementing these? Are there any gotchas or things to watch out for?

Any experience on the cost side?

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  • \$\begingroup\$ Mechanical switches are more expensive. Sometimes, a lot more expensive. And they have a limited life, themselves. But these conductive pads also wear out over time. More so, if made poorly. I completely disbelieve the information on that page about > 10 million uses for a carbon pill type. Not even close. They wear faster than a mechanical switch, in my experience. Just to add something else to look at, have you considered the idea of a glass ampule reed relay with a ring magnet? These are sealed already and are the longest lasting thing I know of, too. \$\endgroup\$
    – jonk
    Commented Jan 29, 2018 at 17:05
  • \$\begingroup\$ @jonk you should make that an answer. \$\endgroup\$
    – Trevor_G
    Commented Jan 29, 2018 at 17:12
  • \$\begingroup\$ @jonk -- I've never looked at reed & magnet in any serious capacity! It seems to me there is a lot of human labor to build these rubber keypads, which is why I'm curious. The mechanical of implementing the keypad in CAD (ie. Solidworks), I loosely understand. \$\endgroup\$
    – Leroy105
    Commented Jan 29, 2018 at 17:15
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    \$\begingroup\$ @Leroy105 I have really hated the widespread use of carbon pill type switches. I have had to, on multiple occasions, repair and or replace such keypads here at home for others. I just plain hate them, now. Didn't before. But I've learned to dislike them a lot having had to "repair/replace" so many times since. By comparison, I still have a full-up working keyboard from 1972 that uses the reed relay + ring magnet on a plunger. It's had a lot of use and it still works today, just fine. Nothing like it. \$\endgroup\$
    – jonk
    Commented Jan 29, 2018 at 17:55
  • \$\begingroup\$ @jonk sounds expensive \$\endgroup\$
    – DKNguyen
    Commented Mar 18, 2020 at 2:44

3 Answers 3

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Does anyone have any experience implementing these? Are there any gotchas or things to watch out for?

I have tested a lot of tactile/membrane keypads in the past and the biggest issue I found was bounce time was very variable between one manufacturer's product and another. This can be annoying if interfacing with a spcific chip (like a DTMF encoder in a telephone) because you quite often got double digits when you thought you'd only pressed once.

If you have a high volume product or a product that gets a lot of keypad use I would seriously consider a lot of mechanical testing of different supplier's products if they do not have a technology that guarantees a closed resistance within a certain time period of the button being pressed. Same when releasing the switch - it can bounce then.

Some keypads I tested that had a seemingly beautiful tactle click didn't actually make contact until you pressed a little harder. Now I'm sure the inducstry has moved-on from those days back in the late 1980s but caution should still be your watchword.

Any experience on the cost side?

They are cheaper on production costs for low to medium volume but don't ignore the time and effort into guaranteeing a good design. The main reason for using them is of course that they can be designed to have buttons in irregular positions i.e. they are easily customizable.

Not wishing to counter anything said by anyone else (@Jonk) but a good technology should give you over ten million operations. We (back then) modified a motorized hack saw like this: -

enter image description here

It produced a repetitive forward and backwards stroke and we used a spring/cushion to set the impact force onto the target keypad. We easily got ten million operations from quite a few but very few could meet the debounce times at end of life.

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  • \$\begingroup\$ thanks, that variability between keypads I would not have considered on the front of things either. \$\endgroup\$
    – Leroy105
    Commented Jan 29, 2018 at 17:45
  • \$\begingroup\$ The thing I hate about membrane keypads is surface wear. Seen a lot of things with the pads worn to the point that they ink is gone and the plastic is cracked, but the button still "works". They really are not great for high usage applications. \$\endgroup\$
    – Trevor_G
    Commented Jan 29, 2018 at 17:45
  • \$\begingroup\$ @Trevor_G, you know what I have seen that got me thinking about this: the Playstation 3 controller. I ripped one apart to change the battery. I saw they were using some kind of hybrid of the approach, it's got a conductive element but a hard button that transitions into something soft. Looks very custom not just a floppy silicone pad. Imagine how hard folks are on their video game controllers! I've seen Chinese use a silicone keypad vs. 5 mechanical switches, and we buy mechanical switches for ~$0.01/USD in Taiwan. How could it still be cheaper! ;) \$\endgroup\$
    – Leroy105
    Commented Jan 29, 2018 at 17:49
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    \$\begingroup\$ Got to love the internet... I tried searching for Worn out control panel Wife looking over my shoulder was not impressed LOL. \$\endgroup\$
    – Trevor_G
    Commented Jan 29, 2018 at 17:53
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    \$\begingroup\$ @Trevor_G and despite all the things I learned about wearing out membrance keypads I still bought a freaking TV whose remote control was unreadable (legend wise) after a couple of years!! \$\endgroup\$
    – Andy aka
    Commented Jan 29, 2018 at 17:56
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So the rubber keypads are less expensive unless you're buying a hand full for a hobby project. They make silicon keypads with compression molding. Similar to injection molding where you make a mold but instead of injecting hot plastic I think it's a powder. There's not a whole lot of labor involved in cranking out a bunch of these. A recent small soft tooling mold cost me $1000.

You do design the button in a program like solidworks, or your favorite 3D tool. And you have your choice of pills, carbon, metal, little click devices. Getting the right feel of your button can be a little tricky though if you don't have experience. Things like shape, wall thickness, material hardness etc all lead to different feeling buttons.

Anyway it's pretty easy to make a button and then have marketing unhappy with the "feel" and have to do it again a few more times till everyone is happy. Also like anything else molded you have to beat the cost of the mold and make enough that you really get your price down. Making 10 at a time will cost you more.

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  • \$\begingroup\$ Yes, I agree we have made these silicone mold for other parts for very cheap (compared to say an actual mold for hard plastics!). I wonder though if there is some poor guy glui'ing "pucks" to the silicone molded piece, that seems like the biggest cost driver. This is really helpful to know that the "feel" is a big driver. Personally I loathe mechanical stuff! ;) We'd call up some up Asian silicone fabrication guys we work with, this is quite helpful. \$\endgroup\$
    – Leroy105
    Commented Jan 29, 2018 at 17:35
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    \$\begingroup\$ Have just got one made, tooling cost $600. @Leroy105 - a worker does indeed manually put the carbon pucks into one side of the tool before molding. When molded, the pucks are bonded to the silicone. Breakout and flash removal are all manual as well. Hence why they are all made in countries with cheap labour. \$\endgroup\$
    – Jon
    Commented Jan 29, 2018 at 18:20
  • \$\begingroup\$ @Jon -- that makes sense. We injection mold plastics with metal inserts, and for how fancy you think things are, it's literally a dude putting in metal pieces in a giant mold and pulling a handle to shoot the plastic around the inserted metal pieces. \$\endgroup\$
    – Leroy105
    Commented Jan 29, 2018 at 18:21
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    \$\begingroup\$ Guess it depends on your volume, but I would agree low to moderate volume would be a guy putting the puck in and cutting them out. High volume is a different game. \$\endgroup\$
    – Some Hardware Guy
    Commented Jan 29, 2018 at 18:21
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    \$\begingroup\$ I've had success in 3d printing a rubber button sheet (4 buttons) with inset legend in ASY Digi ABS / Agilus Black. I used the design guide for silicon rubber buttons from abatek.com/designguide. My buttons press a tactile switch on a pcb - these switches are cheap, and are available in a series of forces - so you can make several pcbs to demo the switch feel. \$\endgroup\$
    – D Duck
    Commented Feb 1, 2018 at 14:53
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There are numerous methods for creating keypads, from expensive individual switches down to cheaper membrane and or puck type keypads.

The decision of which type is best for a particular application can be a difficult one which needs to factor in life expectancy and wear of the switches and of course cost to produce.

The main issue with the puck type, other than they wear out over time, is there is zero tactile feedback to the user. As such issues with "not actually pressed" or "multiple pressed" is rampant with this type of keypad.

A more rugged approach is to use tactile dome switches...

enter image description here

These are mounted on a film that adheres to the PCB which has similar layout to the puck design, and are pushed through a similar rubber and silkscreened keypad which lays over the top. The domes provide good tactile feedback, click, and are reasonably inexpensive.

In the end it really depends on the application and how often the buttons are expected to be pressed and how accurately those presses need to be received.

By the way, there are companies that specialize in and will manufacture the customized rubber part for you. You will find the quality is much higher than something you can do on your own.

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    \$\begingroup\$ I've got a Tivo remote that has a rubber keypad but has a GREAT tacticle response. I can visualize what you are saying with the puck vs. the dome. I bet my Tivo remote has those. I should rip one apart! \$\endgroup\$
    – Leroy105
    Commented Jan 29, 2018 at 17:26
  • \$\begingroup\$ @Leroy105: Indeed, it does. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jan 29, 2018 at 17:36

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