Lummi http://www.lummi.co.uk has been trying out this stuff.
Basically it is a composite material that is an excellent insulator when uncompressed and will transmit heavy currents when compressed.
Sounds interesting - cut into 18mm discs you should get an almost indestructible variable brightness switch. The paper seems to think that heating isn't an issue.
Wonder what it costs?
That's pretty neat. Thanks for posting it.
It's really cheap http://www.mutr.co.uk/product_info.php?cPath=418_464&products_id=1144, and the science principle underneath are delectable.
however its application for lights is somewhat limited by the nonlinear resistance to force (though this kind of works for lighting), the magnitude of forces needed, residual resistance, and the fact it's still a resistor. A light basically has to be fairly well made I think to make it work.
The best really cheap way to do variable lights is already available either with the mode controller/pwm or through the sense pin on regulators, but it's a problem of motivation rather than any tech limitation that they're not common.
Ok, I've thought about it, and it probably wouldn't be that bad even for the cheap lights we have. Basically you just glue it to the center + terminal of the driver boards and it should more or less work pretty well.
Anyone in the UK interested in a group buy? It's only out to a few bucks for each person given it's like 80 or pills so for 10pounds. I'd buy it myself but their international shipping looks a bit nebulous. Or I suppose if enough people in the US were interested I can ship out and split the costs from the UK since these basically fit in any 1st class envelope.
Their postage charges are outrageous for shipping outside the UK. Their minimum order would work out at about $80 delivered to the US.
I have ordered 70 pills at a cost of just under £16 including delivery which works out to about 36 US cents each plus postage to you.
I think they make these things to order so we are looking at China-type delivery times, but maybe not.
Anyone wants some to experiment with - PM me.
Very interesting in did, so in theory you can make a direct driver variable just twisting the body if the rubber pill is located where agentex say above.
The quid is how 'sensible' this stuff is since the battery need some force to make contact anyway.
The very old rheostat's way to control power is not that bad, the Led Lenser headlamp have one and work pretty fine.
I have a CA little engine from 1900 with a rheostat wired in a rectangular piece of stone working good despite his 110 years old.
Many thanks for the news.
A supply of the pills has arrived while I was stranded in the south. The pills are minute!
I was due at work 6 minutes ago so no time to play just now.
First thought, the Tank007 E07 might be a good candidate for trying this stuff out. Its heavy current draw is a turn-off for some.
Can show a photo of one of those please?
Here you go.
This is all 70 of them. Each individual square is about 3-4mm on a side and about 1.5mm thick.
Here is one on the positive contact of one of my beater NiMH cells.
And from the side to show thickness.
Installation is tricky. Obviously you can't use a non-conducting adhesive and these little things seem to leap for freedom every chance they get. I'm going to try a sandwich between two coins of less than 14mm diameter to see if that works better. Or look at some light with a spring post rather than a spring at the tail end.
Maybe glued over the edge on a equally thick rubber with a hole made 'ad hoc' could work.
Would be interesting know the resistance of the stuff half pressed and full pressed, the range must be between 35 ω or less to 0 ω if not has this range I doubt could be used to control a power led.
Not that easy to measure with a multimeter, but I got a reading of 2.5megohms with the probes just touching it. Which may be the conductivity of the wooden desktop.
Sandwiching it between two coins to prevent the very sharp meter probes from destroying the rubbery material I got a resistance of more than my meter could measure >50megohms down to <0.1ohm with a couple of kilograms of pressure.
That's a good idea, I think I have some old inner tubes somewhere which might suit for attaching the stuff