Arduino Forum

Topics => E-Textiles and Craft => Topic started by: funkyguy4000 on Aug 13, 2012, 02:33 am

Title: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 13, 2012, 02:33 am
Hello!

I'm trying to recreate the button pad here https://www.sparkfun.com/products/7835 (https://www.sparkfun.com/products/7835)
I've already got mold made out of wood but I need to know what kind of product I should get to pour over it to make the rubber pad.
I don't own the product.

Anybody have any ideas?
Title: Re: Button pad out of silicone or rubber
Post by: Far-seeker on Aug 13, 2012, 06:47 pm
There are probably some artifical rubber formulations specifically for casting available through arts & crafts stores/catalogs.  Unfortunately I don't have any experience in that area, so I can't make any direct recommendations. 
Title: Re: Button pad out of silicone or rubber
Post by: keeper63@cox.net on Aug 14, 2012, 05:40 am
Liquid casting silicone (and appropriate release) would probably be best - let me dig in my bookmarks...

http://www.smooth-on.com/

They may have something you could use. What do you plan on using for the conductors on the pads? Or do you have a different solution for the switching?
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 14, 2012, 06:06 am
I'm not sure what to use for the conductors.  I don't understand what they mean when they say Part A and Part B.  Isn't it just one product?

EDIT: Also, If I had a RepRap, could I not just print a 3-d Plastic mold and then just pour it in there?
Title: Re: Button pad out of silicone or rubber
Post by: keeper63@cox.net on Aug 15, 2012, 04:16 am

I'm not sure what to use for the conductors.  


Those black rings you see on the part from SparkFun are likely the conductors - generally they are carbon-impregnated rubber (not sure where or if you can easily buy that - but I bet some googling would turn up something). You mainly want something that isn't going to corrode or degrade over time. You might be able to make your own by following something like this:

http://www.instructables.com/id/Make-Conductive-Glue-and-Glue-a-Circuit/
http://www.inklesspress.com/conductive_glue.htm


I don't understand what they mean when they say Part A and Part B.  Isn't it just one product?


Some silicone molding compounds are two-part mixes; some must be measured by volume, some by weight (make sure you're clear on this when you purchase). Basically, one part is the liquid rubber and the other is the "curing compound" - similar to 2-part epoxy. Other silicones are single part compounds containing a volatile chemical that evaporates out as it cures (just like silicone glue/sealant - in fact, you might try that first; just brush it into your mold; though I don't know what you can use as a release agent, which you'll want no matter what compound you use).


EDIT: Also, If I had a RepRap, could I not just print a 3-d Plastic mold and then just pour it in there?


Yes, you could.
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 15, 2012, 04:37 am
Hmmm, I'll add this on to my list of motivation to make awesome apps for money so that I can buy a rep rap
Title: Re: Button pad out of silicone or rubber
Post by: Far-seeker on Aug 15, 2012, 04:15 pm

Those black rings you see on the part from SparkFun are likely the conductors - generally they are carbon-impregnated rubber (not sure where or if you can easily buy that - but I bet some googling would turn up something). You mainly want something that isn't going to corrode or degrade over time. You might be able to make your own by following something like this:

http://www.instructables.com/id/Make-Conductive-Glue-and-Glue-a-Circuit/
http://www.inklesspress.com/conductive_glue.htm


I would image that thin stainless steel washers with the proper inner and outer diameters would also work.  Perhaps not as well but they'd be eaiser to get than the carbon-rubber rings, and might be easier to work with in a confined space than the conductive glue.
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 15, 2012, 05:11 pm
Oh thats true, although every time you press a button, you'd hear a "clink" noise and it would be a lot heavier, wouldn't it?
Title: Re: Button pad out of silicone or rubber
Post by: Far-seeker on Aug 15, 2012, 08:24 pm

Oh thats true, although every time you press a button, you'd hear a "clink" noise and it would be a lot heavier, wouldn't it?


Well it would make the button array measurably heavier, but I don't think enough to matter during use.  I think any noise would depend on a few things, like how far the washer actually moves, how much force is used, and how thick the silicone rubber around it is.

However, I think I might have found something even better...  How about flat copper washers only around 1 mm thick (http://www.grainger.com/Grainger/flat-washers/fasteners/ecatalog/N-8og/Ntt-sealing+washer?Ndr=textsearchesinbase%2Btrue&sst=subset)?
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 15, 2012, 08:30 pm
Would I just glue them on?
GORILLA GLUE!
Title: Re: Button pad out of silicone or rubber
Post by: Far-seeker on Aug 15, 2012, 08:52 pm

Would I just glue them on?
GORILLA GLUE!



Probably, but you'd want to make sure whatever glue you use "plays nice" with the silicone rubber. 

Alternatively with something as light as the copper washers, you might just add them after the rubber has set a while but before the curing process is complete so the rubber sticks to one side of the washers.  I've never tried this though, so I can't guarentee good results.
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 15, 2012, 08:58 pm
Yea, I'm just trying to get ideas.  I've never done this either.
Title: Re: Button pad out of silicone or rubber
Post by: Far-seeker on Aug 16, 2012, 04:28 pm

Yea, I'm just trying to get ideas.  I've never done this either.


It seems like making your own button pad is very possible, but you will have to experiment a little to work out the details of the process.  Please let us know how it goes.
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 16, 2012, 04:52 pm
Will do :)

I think what I'm going to do is just buy a buttonpad, and make a mold out of it and then just use that.
I'd bought some wood to try to custom make it myself....that didn't go well.
Title: Re: Button pad out of silicone or rubber
Post by: keeper63@cox.net on Aug 18, 2012, 05:48 am
The only problem with metal washers is that over time, they will eventually corrode. Stainless steel would be ok, but even it would have contact issues in the long term (which might be longer than you care about the project, though). If I were going to use metal, I think I would go for thin copper washers tinned with 60/40 solder; not as good as gold, of course...
Title: Re: Button pad out of silicone or rubber
Post by: funkyguy4000 on Aug 18, 2012, 06:50 am
Oh thats not a bad idea.  Is that a specific type of solder or will any work?

Lemme just go raid fort Knox and grab some gold real quick..
Title: Re: Button pad out of silicone or rubber
Post by: keeper63@cox.net on Aug 19, 2012, 03:10 am

Oh thats not a bad idea.  Is that a specific type of solder or will any work?


Since you live in the states - you can easily get it (finding it in Europe can sometimes be a pain, what with the RoHS laws and such). Basically, 60/40 solder is a 60 percent tin and 40 percent lead alloy (in reality, it is generally 63/37 - see http://en.wikipedia.org/wiki/Solder). Your ordinary standard electronics solder will work here, but you should clean the copper really well (ideally with weak sulfuric acid - but a good stiff wire brush will work fine, too) and use plenty of flux. Heat the copper well (use a butane torch or similar - a soldering iron won't likely work well, given the size) and apply the solder. You'll want a smooth and even coat, but not a thick one; just thick enough so that the copper doesn't show.

You might also try "dip soldering" the copper, which may make a more even coat: Get a copper plumbing pipe end "cap", and buy some 60/40 solder bar (this will be pure solder - no flux). Mount the end cap in some kind of solid holder (a large vice is a good choice) and heat it up with a propane or similar torch. Melt the solder into the cap so that you have a "pool" of solder to dip into. Remember to wear full protective clothing (long pants, shoes, long sleeves, gloves, eye and face protection). Clean your copper rings, perhaps dip/wipe in flux - then dip the rings in the solder (you might have to fashion some kind of tool to allow for this, of course).


Lemme just go raid fort Knox and grab some gold real quick..


Gold is what is used as a plating when you need the best conductivity and longevity possible for an electrical contact point - it's probably not even possible to do such plating at home, even if you had access to the gold needed (mainly due to the chemicals involved in the process - very ugly). Something to keep in mind, though, is what your contacts on the PCB will be - if they are gold, you don't want solder to contact them - over time they will fail, likely - see http://en.wikipedia.org/wiki/Gold_plating
Title: Re: Button pad out of silicone or rubber
Post by: Far-seeker on Aug 20, 2012, 08:21 pm

Mount the end cap in some kind of solid holder (a large vice is a good choice) and heat it up with a propane or similar torch. Melt the solder into the cap so that you have a "pool" of solder to dip into.


Alternatively, there are small solder pots available at fairly reasonable prices (like the first two in this link (http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&categoryName=category_root&subCategoryName=Test%2C%20Tools%20%26%20Supplies&category=60&refine=1&position=1&history=nq56dyyg%7CfreeText~solder%2Bpot%5Esearch_type~jamecoall%5EprodPage~15%5Epage~SEARCH%252BNAV)).  Not as cheap or adventurous as cr0sh's suggestion, but muc easier to work with if you are going to a sizable batch at the same time.


Clean your copper rings, perhaps dip/wipe in flux - then dip the rings in the solder (you might have to fashion some kind of tool to allow for this, of course).


Or you could just buy a extra large pair of hemostats (http://www.sciplus.com/search.cfm?utm_source=internal&utm_medium=search&utm_content=cf&utm_campaign=celsearchtest&formfield1234567891=36&formfield1234567892=1&formfield1234567894=&term=6273&btnHand.x=0&btnHand.y=0) and wear leather work gloves.