Conductive Paint on Rubber Pad?

All,

I need someone to tell me if I'm being very ignorant of basic electronics.

Basically, I'm trying to set up a very simple circuit (CR2032 battery, LED, and a button) and connect them using conductive paint/ink. I want all of these things mounted on a rubber surface - basically, on the back side of a mouse pad. I tried it out last night and it didn't really work; the first two trials I made my own conductive paint by mixing graphite powder and acrylic paint and I got zero results. The third trial I used Bare Conductive Paint from Radioshack and got the faintest hint of light from the LED (and I had removed the button from the equation at that point).

Is the problem the rubber surface I'm mounting it on? I know rubber is very much not conductive, but I figured that wouldn't be a problem since I'm not running the current through the rubber, I'm running it through the paint on top of the rubber. But is there something I'm just missing here?

Thanks!
Matt

Rubber is an insulator, which is good. If it wasn't, you'd just short out the whole thing.

Bare Conductive Paint is not particularly good at conducting electricity. The more expensive conductive inks are (somewhat) better. You can measure the resistance of your trails of conductive paint with a DVM and see just how bad it is, or refer to the app notes for expected resistance:

http://www.bareconductive.com/wp-content/uploads/2014/03/2014.ApplicationNotes_ElectricPaint.pdf

In any event, putting long trails of Bare Conductive Paint onto a flexible surface is a no-go; it dries rigid, and the first flex of the substrate and it'll crack and crumble off. It's really only good for putting onto point of connection to ensure reliable connection, not distributing power.

You might be better off with conductive thread. It's flexible, and more conductive than the Bare paint, though the resistance is still kinda high.

How about wirewrap wire? 30 gauge, very thin. On the bottom of a mousepad, it won't get enough flexing for the fact that it is solid wire to matter. Resistance is very low because it is just copper wire.

That's a great idea Polymorph, and I had thought of that myself. The reason I've been reluctant to try it is because the pins on the button are very small and short - it's just a tactile switch. I've never done wirewrap before - is it plausible to wrap 30 gauge wire around such small solder pins?

Thanks!
Matt

You can get conducting foam if you want a flexible connection. Often you can get it for free because it is used as packing material for components and boards.

Otherwise just google "conducting foam"

Oh, that'd be very interesting! Any idea where I might buy some to test tonight locally? I googled about but I don't see any listings for it at Radioshack, Wal-mart, etc. Is there a store that sells it?

Oh - yeah, I missed the bit about it being on the bottom of a mouse pad. I would use copper wires no question, and solder them to the button. No need to use exotic materials like flexible thread and conductive paint. AFAIK, nobody does wirewrap anymore.

You got a surface mount button, I'm guessing, so soldering bare wires to it won't be trivial, but not particularly hard in the scheme of soldering. If they're the kind of buttons I'm thinking of ( like these - http://www.ebay.com/itm/100pcs-SMD-Tactile-Pushbutton-Key-Switch-Momentary-Tact-4-Pins-6-6-2-5mm-/221310783283 ), they're dirt cheap, so you can afford to trash a few while soldering.

elveax:
Oh, that’d be very interesting! Any idea where I might buy some to test tonight locally? I googled about but I don’t see any listings for it at Radioshack, Wal-mart, etc. Is there a store that sells it?

Well no idea where local is to you. I can let you have some if you pop round, I am in the Lake District U.K.

elveax,

If you don't already have a multimeter, get one! :wink: This is all going to be VERY difficult if you don't know the resistance of your "conductor". With regular wire or copper traces on a PC board that's usually not a concern because it's usually a fraction of an Ohm, but with conductive paint, who knows?

You can get conducting foam if you want a flexible connection. Often you can get it for free because it is used as packing material for components and boards.

The stuff I've seen is in the megohms... Conductive enough to discharge static but you couldn't power an LED though it.

The stuff I’ve seen is in the megohms.

The stuff I have is less than 1K.

Grumpy_Mike:
The stuff I have is less than 1K.

Over what distance?

Per square. Not a distance.

I'm not saying to -do- wire wrap, just saying that it is very fine generally available wire. 30 gauge. Just solder it, don't wrap it.

Grumpy_Mike:
Well no idea where local is to you.

Seeing he mentioned Radioshack and Wal-mart, I'd guess he's in the USA.

I can let you have some if you pop round, I am in the Lake District U.K.

Your profile says you're in Manchester. Have you moved?
I wouldn't think it convenient for him to pop round from the US. It's even too far for me, in the 'smoke', to pop round! :slight_smile:
But that's another thing that's disappeared from the forum; the poster's location, if they put it in their profile.