tactile switch user interface? - Page 1
Forum section: electronics / beginners

author: dlswenson
author_rank: Newbie
timestamp: September 08, 2013, 05:14:46 pm
content: Hello,I would like to use tactile switches for my user interface. I've seen the custom silicone coverings for these guys -- is that something that a hobbyist can reasonably do or have done? If not, what do you guys use for the "user interface" for your tactile switches?Thanks!-david

author: Zbig
author_rank: Frequent Contributor
timestamp: September 08, 2013, 05:41:21 pm
content: I'd very much like to convince myself that making my own custom button caps is a perfectly valid reason for getting a loan to buy a 3D printer but it's a bit of a stretch even by my standards so I too would like to hear any good solutions for this

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: September 08, 2013, 06:20:34 pm
content: One technique I have used is large button tactile switches under an overlay. Make the holes through the panel a little larger than the switch button so the overlay can flex and adjust the circuit board elevation to put the switch top right at the label when it's not pressed. In the instrument shown below, a thin cork pad (an adhesive cork disk used as mounting pad from the hardware store) was placed on top of the button to get the right height.The result is a switch with a nice feel and a positive click that's as waterproof as the adhesive on the overlay at a reasonable cost. With a lot of use, I've never seen any cracking or failure of the overlay because the amount of travel is pretty small.I first saw this technique used in a Brother electronic typewriter printer interface box.

author: dlswenson
author_rank: Newbie
timestamp: September 22, 2013, 09:00:02 pm
content: Thanks for the reply Jon. That's a good suggestion. I was hoping for a few other suggestions, but I guess this isn't done much outside of professional product development...

author: Unknown
author_rank: Unknown
timestamp: September 22, 2013, 09:40:16 pm
content: Is this going in an enclosure as above or are they just used as is on the PCB?

author: TerminalJack505
author_rank: Super Contributor
timestamp: September 22, 2013, 10:04:20 pm
content: You might pay a visit to your local art supply store and explain what you're looking for. Artists use a ton of different mediums and this might be something they would have. I've seen clays that will have a rubber-like quality once cured, for example.

author: Paul Price
author_rank: Super Contributor
timestamp: September 22, 2013, 11:40:34 pm
content: DIY Sw. Suggestions:(1) Having just ravaged an older HP6110 All-In-One inkjet printer, I noticed that the large front panel had around 30 raised c dome plastic membrane switches for control of fax, scanning, copying, etc. Each of the soft tactile buttons had a black elastomer conductive coating on their underside that contacted an interdigitated contact array underneath when pressed. A good source of free switches, all you need to do is take apart a discarded remote control or printer that has switches of this type and cut them out and then make your custom PCB to locate the switches where you want them and feed the multiplexed contacts to a mpu.(2) You can sandwich alternate pieces of very thin copper foil and polyethylene, PCB material on top, your PCB on bottom to create a tactile capacitor that would change in capacitance by pressure and return to its pre-pressed capacitance upon release. These capacitive switch elements could be the freq. determining capacitors in individual LM324 op-amp oscillators and a MCU can determine a tactile press by the individual oscillator frequency change.(3) You can use an interdigitated switch contact area on a PCB board. One side connects to a common LM324 approx. 200KHz oscillator and the other side connects to a 100pf capacitor to a 1-meg resistor to a 1N4184 diode to a small filter capacitor (10nF) shunted by a 4.7meg resistor to rectify the voltage then presented to individual LM339 comparator inputs. A finger pressed upon the interdigitated contacts would produce a MCU detectable switch contact state.(4) You can create a simple push-button tactile switch by sandwiching two sheets of thin copper stock attached to double-sided tape with a thin sheet of polyethylene that has a .2-in gap under the switch pressing point where a contact can be made by pressing so as to deform the copper strips to make a momentary contact. The top strip of double-sided tape comes with a protective white covering that provides a switch press surface you can retain as a pressing surface. You drill holes in the interface panel big enough for a finger press or other pressure transferring surface for actuating over the press-switch active area.For extra funk, you can substitute aluminum foil for the copper strips mentioned above with the drawback of having to use wire-wrap techniques to connect areas of your custom switch array PCB to each of the switch contacts.(5) For a truly proportional to pressure tactile switch you can mechanically couple two large red bricks to a transducer coupled to the surface underneath, of course buffered by a suitable large flat board type of front panel that exposes each brick while fixing their location. Simply stepping onto one or more bricks can encode a virtual unlimited number of analog states and up to 3 different active digital states that can be detected by use of the required strain-gauge or load cell outputs.