Mambrane Switches on the Power Pro

[jsburger]

In another thread RFGuy said:

" I have used someone else's PowerPro a few times and they are nice, though I am not a fan of the membrane switches on it (personal preference)."

We have heard this in the distant past but not much lately. He said it was a personal preference and I respect that.

So what is the problem with membrane switches? They are all over the place and have been for meany meany years. My gas stove, my refrigerator, my microwave all have them. I have never had one fail in all the years I have owned items with a membrane switch.

Is it the lack of tactile feel? We all own smart phones. Absolutely no tactile feel there. The touch screen on your car's display has no tactile feel.

[RFGuy]

As an engineer I hate how unreliable (prone to failure) most membrane switches are so it is my disapproval of a bad design choice. As a consumer, I dislike the feel of the membrane switches. It is the texture of the switch that I don't like and doesn't feel good to the touch, for me. Again I recognize this is personal preference and many may disagree on this...

Not necessarily saying this was Shopsmith's design decision on the membrane switches. I see them on all of the NOVA products with DVR motors so they are very similar to the PowerPro. My guess is StriaTech/NOVA made this choice.

[jsburger]

As an engineer I hate how unreliable (prone to failure) most membrane switches are so it is my disapproval of a bad design choice. As a consumer, I dislike the feel of the membrane switches. It is the texture of the switch that I don't like and doesn't feel good to the touch, for me. Again I recognize this is personal preference and many may disagree on this...

Not necessarily saying this was Shopsmith's design decision on the membrane switches. I see them on all of the NOVA products with DVR motors so they are very similar to the PowerPro. My guess is StriaTech/NOVA made this choice.

OK, but how are their membrane switches different from all the other millions out there in the world? I have never had a membrane switch fail since they were first introduced or since I have owned them since they were first introduced. I am old enough to have grown up in my early years before TV.

Now I don't know if this is a membrane switch but I have had more than one failure with remote controls with discrete buttons. They have a rubber membrane under the buttons that I assume is conductive. Push the discrete button and the pad contacts the PCB and closes the connection. I have many of them fail over the years. I suspect because the discrete buttons on the device are not sealed. Membrane pads as I think of them today are completely sealed from the users prospective.

[RFGuy]

OK, but how are their membrane switches different from all the other millions out there in the world? I have never had a membrane switch fail since they were first introduced or since I have owned them since they were first introduced. I am old enough to have grown up in my early years before TV.

Now I don't know if this is a membrane switch but I have had more than one failure with remote controls with discrete buttons. They have a rubber membrane under the buttons that I assume is conductive. Push the discrete button and the pad contacts the PCB and closes the connection. I have many of them fail over the years. I suspect because the discrete buttons on the device are not sealed. Membrane pads as I think of them today are completely sealed from the users prospective.

John,

I have personally seen membrane switches fail first hand on products that I own and 2nd hand on products other people own. There are many different types of manufacturing processes for switches. Membrane switches are one subset and the type that the PowerPro uses are a further subset of this. In a related category are remote control style membrane switches. These use silicone buttons that are the membrane which sit on top of gold plated PCB trace contacts. Typically these fail when enough dust/moisture gets into the space between the conductive contacts on the back of the membrane and the PCB trace to make the connection. If you can keep contaminants out, the remote controller style membrane switch can last a long time but in the real world they do succumb to the elements. I have had select buttons get difficult to activate on remote controls over the years. Rarely do they complete fail, but just get more and more difficult to use with time. At present, I have a cordless phone in my house that it is very difficult to get the "1" button to depress but the rest work fine. Of course the reason is that the probability of a "1" being depressed is much higher than you think because of automated phone systems where you press it to get through a menu selection. Now for the PowerPro, I haven't taken one apart, but I believe they are using a bubble/dome type of membrane switch. Most likely of this design (https://butlertechnologies.com/products ... s-keypads/). The claim to fame of this type of switch is it is better sealed from the environment with a plastic dome cover that you press, so dust and moisture are much less likely to contaminate the switch. The main difference between this type of membrane switch and the remote controller membrane is there is a lot more mechanical stress on the PCB as these sandwiched polymer layers that form the dome are depressed. I have had some appliances in the past with this style switch and they do fail as well, typically with a concave dome. I have seen at least 1 or 2 complain of this on the PowerPro on this forum. Also some cheap computer keyboards use this type of membrane switch and I have seen them fail at work before on different keyboards. Typically these membrane switches are rated to have a life expectancy of a few million presses, but in reality I think that is more aspirational than actual. I mean, I haven't pressed the "1" button on my cordless phone 1 million times, but then again it does still work - it is just very, very hard to press to make it work. In comparison, a high quality mechanical switch, like you find on gaming keyboards, factory machinery equipment panels, etc. are often rated at 100 million activations for life expectancy. When they fail, they fail, but I have never seen/heard of one that was difficult to operate before the failure, i.e. they operate like new for a long, long time unlike a membrane switch.

Then there is the actual feel of the switch. Often these membrane pads like on the PowerPro are covered in a textured plastic. I don't like the feel of them; kind of feels like nails on a chalkboard sounds. Then there is the haptic response which can be a positive or a negative. I much prefer the mechanical click and depressed feeling on a mechanical key over the little bump feeling when I press a membrane dome switch. Again, this is ALL personal preference. Think about typing on a virtual keyboard on top of a tablet or phone versus using a computer keyboard. Some people have no problems typing on a virtual keyboard with no auditory/tactile feedback from the keys while others can't stand them. It is similar here. I am just saying the interface on the PowerPro is not my favorite, but if someone gave me a PowerPro for free I would use it though I still wouldn't be happy with the membrane switches. Perhaps I would like it better if the buttons were a bit bigger like what NOVA does on their DVR control panels. Even better would be a good size LCD touchscreen instead of the membrane switches. I'd take the compromise of potentially lower reliability to have a touchscreen interface on a PowerPro over membrane switches.

[JPG]

When I think of 'membrane' switches I think of layers of plastic sheets with conductive elements on the outer layer. The 'middle' layer consists of a hole. The third layer also contains conductive elements but is rigid and fixed in space. When depressed the outer layer moves(barely perceptible to the finger) into the hole and contacts the rigid layer.

Carbonized rubber dome switches have a rigid layer of conductive elements. The dome has a protruding nub at the 'top' of the dome facing the concave direction of the dome. This nub has a carbonized surface facing the rigid layer. When pressure is applied(usually from a movable key button) the dome collapses and the nub contacts the rigid layer. This provides both motion and force varying feedback to the finger applying the force. The rubber can result in collapsing and the carbon can be depleted. My computer has one dead key and several unreliable keys. Needless too say I am not now a fan of this type of keyboard.

I recently had to use an IBM original keyboard and now dislike the 'excessive' motion it requires. Back 'then' I liked it very much. So it seems it is about what we get accustomed to.

So rubber dome gets my vote as long as the rubber behaves and the contact is realized. When not, it gets my ire!

OH! Then there is the metal collapsible dome type(think Atari joystick controller using 4 switches). Metal fatigue gets the bad rap there.