Hello.

I have been trying to figure out a good way to make membrane switches. I want to make something like this test design i made into a pendant:

http://www.clockworkchicago.com/pendant.jpg


Anyone seen any sites about DIY membrane switches?

My current idea involves small PCB pushbutton switches, clear inkjetable window sticker material, and some sort of ridgid top layer with button cutouts.. so it would be a membrane switch under a shield, sorta... not exactly what i want..

i even foolishly loaded a sheet of thin white thermalplastic ive got into my inkjet and tried that - thinking i could make a mold and vacuum form a panel..


ideas?

What are your plans for interfacing that with a computer?
Are you designing custom electronics too to work with the rotarty encoder, and led's inside (I assume there's a power led, etc.)

My only suggestion would be to make a more basic 3 axis version as well, without A axis features or the f keys, probe and 2 aux buttons. The jog dial is excellent. I'd likely buy one.

EDIT: what about qtouch IC's? http://www.qprox.com/ I've used them and they're pretty cool. A qtouch rotary dial as well (like the ipod clickwheel) would be amazing. I don't know of a cnc pendant like that.

Edit2: here's a link specifically to the rotary encoder http://www.qprox.com/products/qwheel_qt510.php

wow. it is $100..

i was planning a combonation of parallel port pins, keyboard output(via a usb keyboard PCB)... a mouse encoder or a simple slotted disc and optical sensor for the mpg...


cheap and easy. some of the LEDs are just for this version, as there will be several prototypes.

Printing on thermalformable plastic with inkjet... that is what i want, pretty much

Vacpress -

I am not an electronics dude, but when you get moving, I want one. I can maybe pitch in for some of the R&D costs and help you out that way, but when it works I want to buy one - for sure. Keep me in mind - please!

Scott

xtras-no prob...

in fact, if someone could cnc me a mold for vacuum forming some tests, they would compensated.. especially if they could 'support the development' which would be upto 3 or 4... hmm 10x12x.25 " 'molds'.... details to follow..

i would mail you a block of REN modeling board. a very nice material that cncs like wood but has a much more regular grain, being some sort of expanded foam...

im not sure... if i can find an easy way to make membrane panels, they could be cheap... other options would be pushbuttons and a milled faceplate with inkjet printed graphics sandwiched...

modern inkjets can produce very nice control panel art, i am sure.

ya'know,

come to think of it, i dont even need a mold machined, i just need some sort of 'inserts' i can glue or tape down or something to make test panels..

ive got this idea that i can use some sort of flexible glue and tin or copper foil, glued into the 'top' of a 'pushbutton' molded into plastic.. when pressed it would hit a PCB below...

illustrations will follow.. i have been so busy.. incidently, i tried putting some pushbuttons under a piece of thin plastic with an inkjet printed transparency on top.. it was too difficult to press and the buttons had to be far apart, and it took alot of effort to make... an ideal assembly would be 2 or 3 layers... pcb, buttons of some kind, printed panel.. comercial makers use these weird metal things, but then i need to be able to mold an allready printed piece of plastic again..

Ugh. I am sure my long-windedness will kill my own thread.

You could try ripping apart an older caluclator or adding machine. I tore one apart once since it had stamped metal triangular shaped "domes" under the buttons, the 3 corners acted as one contact and there was a dimple in the center that was the other contact. Pushing in the center would make it sort of "pop" down in the middle and make contact.

Opps, just read vacpresses last post. Same thing.

Also chech out these very thin switches from ALPS
http://www.mouser.com/catalog/625/1167.pdf
I think they have a similar metal peice in them that you could maybe rip out and use in you own design.

You could always eBay some old 'Lights Out (http://pics.hoobly.com/full/d643681fe9e28a99d7fd54de9adb2a6f.jpg)' games and scavange the really nice lit rubber switches from them. The only buttons you have on there that aren't square-ish are the 'manual control' sections.

Just find someone that can print on Adhesive Vinyl to do the overlay, and the buttons would come up through that...

Only the eval board is $100. The rotary touch IC itself is about $5-6. The alps switches look nice, it would be nice to feel a real click when you press the button.

i would mail you a block of REN modeling board. a very nice material that cncs like wood but has a much more regular grain, being some sort of expanded foam....

I am familiar with it and I can (and am willing to!) do this kind of stuff if you don't get any other more attractive offers. I am also familiar with molding urethanes in small quantity, custom runs in 'budget' tooling.

I don't have any ideas for the electrical side of things but I am willing to pitch in for the mechanical and molding side of things to bring an attractive, functional package together.

Scott

yes. i want it to be ultra simple... as much as can be done by etching a PCB and molding a single piece of plastic, ideally.. the comemrcial makers all have crosssections of their designs. unfortunately most seem to rely on either conductive ink printing, printing onto moldable plastic, or both..

the hard part, really, is printing on a piece of plastic which can then be molded.. a google search of 'inkjet vacuum form' and 'inkjet plastic' gave no good results.

What about maybe using a water clear urethane skin and a thin nylon film behind,then mold together? Can you print on nylon film? Would it survive?

Just tossing out ideas... might not be good ideas but ideas none the less!

Look at the gas pump keypads - they are perfectly flat w/o bumps. What if you made a thin spacer to keep the contact film off the board and when the key area was depressed it made contact - you know? The face of the keypad could then be made flat and could open up a few more options.

Scott

The only idea I have is those iron-on t-shirt transfers. Not sure how that would work..or look. If you reversed the image and put it on the back....maybe?

I have a DIY idea, that might be easier than trying to figure out the conductive printable formable plastic part.

Basically a spring loaded normally closed group of buttons all connected to a ground plane through the springs. They make contact with a pcb flipped copper down forced closed by the springs. A small nub sticking through a via in the pcb is able to be pressed to open that switch.

I'll see if I can work up a drawing to better explain this, tools are limited here at work.

I went digging in my Pile O' Stuff and I found a control panel that has an overlay that is EXACTLY what you are looking for. So, I took it off and scanned it for you...

http://users.adelphia.net/~javamoose/Membrane/Membrane_Front_Small.jpg (http://users.adelphia.net/~javamoose/Membrane/Membrane_Front_Large.jpg)
-=-=- Click for Larger View -=-=-

The top feels like thick vinyl, possibly screen-printed, however I think heavyweight adhesive vinyl (sign shop) would work as well.

http://users.adelphia.net/~javamoose/Membrane/Membrane_Back_Small.jpg (http://users.adelphia.net/~javamoose/Membrane/Membrane_Back_Large.jpg)
-=-=- Click for Larger View -=-=-

Now, the underside has the printed conductive-ink traces - which you said you can't do (at least, not easily or low-cost).

Looking at this, and thinking of how I would low-tech it - I may have come up with a solution that might work for you.

http://users.adelphia.net/~javamoose/Membrane/Enclosure_Small.jpg (http://users.adelphia.net/~javamoose/Membrane/Enclosure_Large.jpg)
-=-=- Click for Larger View -=-=-

Basically you would have a Circuit Board with Microswitches mounted to the back of your control surface. The control surface would have holes drilled in the locations of the switches that would allow them (switches) to be flush with the top of the control surface. Then your Adhesive Vinyl Overlay Graphic would go on the top of the control surface. Bada-Bing, inexpensive and fairly simple "professional" membrane interface! :cheers:

javadog.

Thanks for the detailed reply. That is actually EXACTLY what I have tried thus far. The problem was the printed transparency sheet on the thin white plastic sheet were too hard to press reliably. multiple buttons got pressed.

It is actually possible to silkprint conductable ink, and it is actually easy to silkprint onto plastic sheet that is then vacuum formed (i know all about these 2 processes, vacuum forming and silkprinting)...

unfortunately making a silkprint stencil is quite alot of work, and my design is... 4 colors.. ugh. that puts the cost for the first panels printout around $40, at least, for silkscreen, emulsion, ink, etc...

an ideal solution though, could use silkprinting. i have silkprinting equipment.. i just would MUCH prefer to inkjet print.. I would imagine I may make about 20 of these..maybe 50... silkprinting multiple-colors is just not economical at those low volumes...

One thing i maybe could have done that would work is to just heat a 1/2" steel rod and use it to make little divits in the plastic..

If you search the web you can find another solution used in industry.. Basically little metal 'doodads'... sort of a third sphere, with clearance for a trace to come out under it, and when you press down it has a tactile response.. you solder these right to a pcb, and then glue the plastic overlay with similarly molded 'button' dimples vacuum formed in...

this is just 3 layers.. pcb, metal thingies, graphics...

the real question is how these pro shops produce their prototype graphics..

any ideas? tell me more about these adhesive vinyl stickers... if i am thinking of the same thing, they can be inkjet printed... but they canot be molded..

incidently.. inkjet printing onto the 'just barely too thick' thermal-plastic ive got resulted in a very smeary mess. i cannot tell if it was because the material was too thick, or if it was the surface...

someone out there MAY make a product that is like inkjet transparencies - slightly textured - but for thermal forming... i couldnt find it though...


another idea is water-slip decals.. but something tells me they dont hold-up

Hi, I think this is what you want "in the metal". I chose separate keys because those membrame boards aren't durable and tactile. Every key has it's own bore to prevent accidental dual keying. This construction is what farmers hammer away on, they didn't destruct anything yet. It's covered by a laminated print, the thinnest variety of heat laminate.
Carel

You should contact some sign-makers in your area and see if they have a wide format solvent printer or thermal printer, they would be able to print to a vinyl substrate that wouldn't make a smeary mess when you tried vaccum forming.

carel,

that looks nearly identical to what i had worked up at 3am last week.. minus the LCD screen...

I couldnt get a reliable or satisfying feel with any material i covered the thing with...

im not sure about forminy vinyl.. we always used this white HDPE sheet (if i remember correctly. someone else did ordering, i built the vaccuum forming equipment and designed some of the products... cant remember what we ended up with in stock though. it was 3 years ago)


shay,
we silkprinted onto plastic with great results, really fantastic, using the t-shirt printing ink.. My theory is that the heat from the vacuum former melted the little vinyl globules in the ink, or whatever, and fused it to the plastic. the result was very nice..

however, silkprinting multiple colors is a last-case scenario for me on this project...

grrrr. another issue with forming printed materials is distortion. but i think the really slight relief of the buttons should have little effect...

thanks!

Well, what is called "ABS" in Europe will do the job. They make suitcases, bumpers etc. from it. Google showed LEGO is made from the stuff. It can be formed and the most important: it is cheap. About multi-color, it's industrial thus B&W.

Carel

sure. ABS.. i beleive we usually call it ABS or styrene in the states.

it till needs to be printed on. this is the hard part!

also, i would imagine one can get ABS formulated to most any color. its maybe the most common plastic for injection molded parts?

incidently.. inkjet printing onto the 'just barely too thick' thermal-plastic ive got resulted in a very smeary mess. i cannot tell if it was because the material was too thick, or if it was the surface...

What brand printer? HP's ink is water-based, and will always smear on plastic (not on their coated transparencies though). Epson has printers with a pigment based ink system that will not smear, well - might not smear.

You should contact some sign-makers in your area and see if they have a wide format solvent printer or thermal printer, they would be able to print to a vinyl substrate that wouldn't make a smeary mess when you tried vaccum forming.

That is exactly what I was talking about when I was mentioning 'adhesive vinyl'. I was talking about the heavyweight vinyl material with the self-adhesive backing that would make it easier to put onto your control surface.

The solvent based plotters (would not go thermal) are waterproof, and the low-heat that it will take to put the little 'bubbles' for the buttons shouldn't mess up the printing at all. Call your local signshops, tell them what you are doing, see if you can get a sample overlay printed to "test" before you order.

Personally, I don't really see the need to vaccum form the overlay - but I understand what you are going for...

Java, I did a control panel for a test fixure simalar to the way you described. The over lay was screen printed on very thin polycarbonate, regular vinyl will wear pretty quick unless laminate with somthing.
It worked ok, but the spacing has to be just right or it feels weird.
There might be a way to make one like the one you scanned. What about the silver conductive "circut repair pens" to make the traces on the flexable part? I have used them to fix connections on a dart board that used the same type of swithces in the score board. Just sort of "draw" your own circuit board on some mylar or thin lexan. The only problem I see is how to connect it to the outside world. The conections on that type of thing are usualy some type of "edge" connector or has pins crimped to it. (this was the problem with the dart board, the connection to the pins was loose/corroded so I used the pen to bridge them back to the traces)

A side note, I have a 54" SolJet printer that can print on almost anything you can fit in it that will take the ink. Being solvent based it wears very well and could all so be laminated over or stuck to something. Much better than plain old ink jet. If some one wants to try something like this I could print them very reasonably on a material to be determined. (if it is on vinyl, it can also conture cut the shape/windows in it)
PM me if interested.
ED: By the way Vacpress, I am also in the Chicago area.(Melrose Park/Aurora)

$6 usb keyboard http://www.newegg.com/Product/Product.asp?Item=N82E16823107127

I'm in Illinois as well (Barrington)

If you plan on using a USB encoder, keep in mind it will only work wile our control software is running as the primary window on windows. Is there a way in windows to force a program to run in front all the time?

Arturo Duncan

Lwill, see PM.

arturod-

well. with some of the secutrity software to setup public systems(inet cafes, pos, etc) you can have it keep one single program in the foreground at all time... sure.. this might even be a good idea for a dedicated cnc control system... id iamgine there is some freeware somewhere that does it also..