Boxes, buttons and switches, could this work? - Page 1
Forum section: electronics / projects

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 10, 2015, 06:09:33 pm
content: Notice: For everyone not wanting to read much, pretty pictures further down below.Hello!I have decidet to put together a few small handheld thingys.A display, battery, regulator, micro, storage, RTC, a bit of prototyping area and everything in a tidy enclosure.I would like it to look fairly pretty, i have hacked together so many things over the years i want something that looks like someone who knows what they are dooing build it.I got everything figured out, working prototype done and i spend way too much time selecting the right display and enclosure to make it look good.But i am stuck at this last bit, the human interface or otherwise known as, the buttons.They need to have a decent tactile feedback, nice and klicky, not mushy, spongy, wobbly or otherwise horrible. Because my phone could do everything better then this thing i am building.But phones have a atrocious battery life and touchscreens alone are the devils work.The first solution would be something like this, fairly obvious.Dirt cheap, somewhat reliable, easy to put together but it looks horrible:Now, i could put a few caps on those buttons, that makes it look a bit better.But that is still kinda horrible looking, i think.Both of these have one mayor flaw, they need a good deal more then 3mm height, i would like to keep everything as flat as possible.I have been pulling apart gear since i could hold the screwdriver, i know how the big boys do it.But custom keys, caps and everything else either has to be ordered in bulk or sourced out of china with no guarantee that it is still available next week.So i thought about what tools i got, what i could make myself and what could be made with a simple hand cranked mill.This is what i came up with:The switches could be replaced with some very low profile but i allready had the model of those and dit not want to draw another.There is maybe a very faint memory that i have seen something like this, but i could not find another example. Mostly because i could not think of the right search words.The travel of each tab is limited to keep everything within a plastic deformation range.The lateral range of motion is guidet by the tab as well. Maybe they need to be thinned out a bit on the back to make it more flexible.What do you think?Do you have another suggestion for a low cost, low volume, nice to look at button solution?Greetings,Peter

author: Ian.M
author_rank: Super Contributor
timestamp: April 10, 2015, 06:42:49 pm
content: The last one is horrible and unreliable. The machined out slots trap dirt, and sooner or later the plastic will fatigue and buttons will start dropping off unless its a very thin sheet, which will just feel nasty.If you really cant afford the depth required to use button caps, you should be looking at metal tactile click domes. Your PCB forms the contacts, which should be gold or tin plated depending on the plating of the domes. Each dome needs a vent hole through the PCB under it for a satisfactory feel. This can be the via that connects the centre pad. You then need an insulating spacer sheet with a hole in it for each dome, with double sided sticky tape also punched with the same hole pattern on each side, your legend sheet printed on something like mylar drafting film and clear fablon on the top. The result could easily be as professional as any tactile membrane keypad on an appliance that doesn't have embossed key surrounds

author: MasterBuilder
author_rank: Regular Contributor
timestamp: April 10, 2015, 09:21:26 pm
content: Try fitting the PlayStation 2 d-pad or x, circle, square, triangle buttons. These are the best buttons I know of.I don't think using an unconventional design here would be wise.

author: Arseneau
author_rank: Newbie
timestamp: April 11, 2015, 01:32:13 am
content: How about replacing all of those buttons with capacitive sensing?

author: Ian.M
author_rank: Super Contributor
timestamp: April 11, 2015, 02:29:02 am
content: Cap sensing wont have a nice tactile click. However I suppose you could add a solonoid 'thumper' to the back of the front panel. Its actually probably the easiest way to do this - black soldermask over the whole panel. Tented or filled vias so there are no nasty holes in the keypad, and key outlines and legends done in silkscreen.

author: SL4P
author_rank: Super Contributor
timestamp: April 11, 2015, 04:09:54 am
content: Rout out the PCB with small square holes, and mount the body of the tactswitches soldered from the rear- that way you lose the thickness pf the PCB, and the tact leads... >1.5mm thinner.I agree withthe slots being a half-assed solution. Stay with the buttons & caps - ideally with a skirt to stop direct splash ingress. Also consider if splashes do get to the 'flange' on the caps - that it can 'drain' out before it reaches the PCB/switches... sometimes a thin plastic sheet with snall jholes just the size of t he seitch stalks - that is slightly larger than the PCB area... so that any ingress has to a) get through the front panel, b) past the cap's flange, and then c) past the thin plastic sheet. This will catch probably95% of any incidental liquid thrown at the panel. (not immersion!)Another factor is tolimit the travel of the button caps(not the switches) - to stop people that 'mash' the buttons too hard. Otherwise regardless of how the switches are attached - they will be rattling around the bottom of the case.Next step - perfect v0.1 and then KickStarter as a generic front panel platform.

author: ivaylo
author_rank: Frequent Contributor
timestamp: April 11, 2015, 07:07:38 am
content: Someone was telling me they got something like thishttp://www.everychina.com/p-z51d9ba6-90551209-waterproof-tactile-rubber-membrane-switch-panel-adhesiver-sticker-odm-are-welcomed.htmldone for under a $100 by one of these Chinese shops? I think, have to ask... A batch of 10 or so for that price. Not bad quality too, I saw the final version.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 11, 2015, 09:34:29 am
content: Quote from: SL4P on April 11, 2015, 04:09:54 amEhhhhhh.... that sounds really, really weak. When you push on it, it's not being pushed against the board, it's yanking directly on the leads. It'll fatigue in no time.That is a good way to deal with component height though, sometimes -- you can even buy "rear mounted" SMT LEDs by the reel.I would suggest looking at membranes. They're cheap (well... in modest quantities), available with reasonably clicky feels (the aforementioned buckling-dome types), can have LEDs inside or alongside them, and not to mention the freedom to print anything and everything on the overlay (including transparent windows for displays, or translucent holes for PCB-mounted LEDs to shine through). Electrical performance is good (usually fully blocks ESD voltage, though I still wouldn't recommend omitting ESD protection on the wires), it's reasonably tough (if not scratch-resistant), and it's fully sealed, no cracks to worry about (with a suitable adhesive backing and sealant, leave it outside in the rain for all anyone cares!).Tim

author: SL4P
author_rank: Super Contributor
timestamp: April 11, 2015, 10:04:50 am
content: Quote from: T3sl4co1l on April 11, 2015, 09:34:29 am...is to limit the travel of the button caps (not the switches) - to stop people that 'mash' the buttons too hard.Using the PCB to limit the button travel is not much better than using the switch itself to act as the mechanical limit...Also - those leaded LEDs with 'side leads' work well in this 'through-hole' method.(And another trick if using illuminated switches - is to only light them when the particular switch function is valid (and processed by the code) - sort of 'guided' operation to the user...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 11, 2015, 10:45:35 am
content: Quote from: SL4P on April 11, 2015, 10:04:50 amAhh, I gotcha.Though that assumes that the button caps bottom out against the PCB, just before the switches bottom out, and just after the switch clicks. So you'll need some really lucky picks on switch height, cap size and PCB thickness.I still don't think the "hanging by solder alone" trick would be reliable against normal actuation force though. Obviously, it'll last longer than some guy punching it and breaking it in just one cycle.. but no idea how long after that..QuoteAh yup, those would work too (with only a little work to trim the leads, no bending as required for conventional T1-3/4 etc. styles).Be neat if there's a switch with a hollow backside and a translucent cover, so you could put one of these LEDs behind it and light it up... maybe there is, and I just never saw one, because I browse switches so rarely...Tim

author: SL4P
author_rank: Super Contributor
timestamp: April 11, 2015, 11:45:31 am
content: This whole discussion comes back to the simple fact that - whenever I've designed anything for manufacture - the enclosure, connectors and user-facing-controlsoften account for 30% or more of the BOM- excluding r&d costs).The actual electronics is cheap, and assembly effort can be minimised with careful design and section of methods... but the physical bits are a bi#ch! (e.g. avoid *any* hand wiring or manual assembly of parts other than clamping the outer shell together! Even pushing crimped pins into connectors and plugging those connectors can quickly add up to serious $labour when making 100, 1K, 10K units!). The setup costs for surface-mount / pick & place & stencils is minimal (say $2.5K) compared to the the time needed, and cost of manual stuffing the connectors and through-hole parts etc on 500 pcs of a $100/unit product ($50K)It can be more cost-effective to ask the manufacturer to customise theirstandardproduct for an extra $2K per order, than to spend $5K having labour fit, solder, trim the same parts from the stock parts bin. The trick here is to coordinate logistocs to get the parts into the assembly queue when they're needed - don't stop the production line!Polycarbonate / mylar switch membranes come into this category - but only for some applications. The mylar file will age, split/discolour over time - and can be damaged by a simple fingernail, tool, or sharp mechanical impact. Horses for courses.

author: ciccio
author_rank: Frequent Contributor
timestamp: April 11, 2015, 01:42:11 pm
content: Look at this amplifier:http://www.montarbo.com/en/prod/581/PLM6800The front panel is made with avery thin layer of inox steel, with laser etched lettering and laser cut slots that are similar to the OP third proposal.With careful design, even if there are two powerful cooling fans, there is no problem with dust or dirt, at least in the 5 years that the unit is being manufactured. The only problem I've seen is that laser etched lettering is not well readable in low light.Best regards

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 12, 2015, 03:18:49 am
content: Hello everybody and thanks for the replys!There was some good feedback, i will do some more twiddeling with the cad program and will get back to you with a more detailed reply!

author: calexanian
author_rank: Super Contributor
timestamp: April 12, 2015, 06:43:26 am
content: In low quantity any of your options would be just fine. You have to just get the press actuation force of your tact switches to feel good. For a commercialized product membrane switches are the most commonly used. Cap sense is more of a consumer low end type application. We usehttp://www.lustrecal.com/content/?id=96this company for all of our front panel overlays. Of course we are in the U.S. but I am sure you have similar companies there.

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 15, 2015, 02:39:02 am
content: Now that i had a few days to think...Dit not think about grime seeping in the grooves, that is a good point!The gaps would not seal that well either.Yes, routing the buttons into the enclosure is a bad idea.Capsense would make the whole thing easy but i hate touch interfaces, i need to be able to feel the button and get a feedback without lag and this should work with gloves.A membrane keypad would be ok, but i can not source one that will fit, has the right buttons on it and a custom one is not feaseable.The space i have available is about 3mm, that does not leave that much room...There were a few very low propile buttons on ebay, i bought 50 of them for a fiver:http://shiosai.de/gallery3/var/resizes/Electronics/Cheap-low-profile-SMD-switch-/20150414_185534.jpg?m=1429031271Metal dome switches in a small body, they have a nice klick and i can get them in higher qulity too.I ordered a few new single flute bits for my wanna-be mill setup since i will have to make the rectangular cutouts annyway so i decidet to get way, way too fancy...This is just a very, very rough mock up.The dimensions are all askew, parts are missing, holes missing, this is just to get the basic idea. They would be fixed to the PCB with screws, the center one with a little rubber pad as a pivet point in the middle.They are designed in a way that should make it very easy to cut a houndred of them fairly quickly with a big router bit and slit saw.Maybe 3D printing and vapor polishing could be possibility, allthough i do not think that would be sturdy enough and i have no experience with 3D printing.The biggest PIA would be the drilling of the plunger holes into the bottom of each button.Each button would have about 0.3mm free air travel before engaging the metal dome switch.From past experience im comforable with saying that the little "swing arm" should not wear out at such a short travel distance.That might be a horrible tight tolerance but could be increased with shims.