conductive rubber switch question

[tempus fugit]

Hey all;

I'm designing a switching system using a uC and am thinking about using some
of those little conductive rubber switches to short an input to ground to
the uC. I had planned to use the pullups on the uC, or use 10k resistors as
pullups. Will the conductive rubber be able to handle the small (I guess
5/10 000 = 0.5 mA) of current or do I need to use something more robust?

Thanks

 

[Jasen Betts]

On 2009-01-19, tempus fugit <toccata@quitspammingme.ciaccess.com> wrote:

Hey all;

I'm designing a switching system using a uC and am thinking about using some
of those little conductive rubber switches to short an input to ground to
the uC. I had planned to use the pullups on the uC, or use 10k resistors as
pullups. Will the conductive rubber be able to handle the small (I guess
5/10 000 = 0.5 mA) of current or do I need to use something more robust?

10K is probably too small, try 100K (or the internal pull-ups)

if you're (still) worried about heating of the rubber turn the pullups off
while not needed.

 

[Eeyore]

tempus fugit wrote:

Hey all;

I'm designing a switching system using a uC and am thinking about using some
of those little conductive rubber switches to short an input to ground to
the uC. I had planned to use the pullups on the uC, or use 10k resistors as
pullups. Will the conductive rubber be able to handle the small (I guess
5/10 000 = 0.5 mA) of current or do I need to use something more robust?

It should be on the data sheet.

As Jasen says, I'd tend to err on the higher side for pullups (or indeed use
internal ones).

Graham

 

[Nemo]

I would think the conductive rubber will be able to take 0.5mA no
problem, though the datasheet will say for sure. Consider the surface
area dissipating the power, and compare with a resistor. In general, a
relatively high current like that will make the input more reliable. My
reasoning is thus. If the pullup is as high as 100k, it is easy for RFI
/ ESD to generate a false signal. The extra current drain (0.5mA versus
0.05mA) is only momentary so is not relevant to battery life, if you're
using batteries.
--
Nemo

 

[tempus fugit]

"Nemo" <Paul@nospam.nospam.nospam.nospam.co.uk> wrote in message
news:luwNIVJiI5fJFwx9@furfur.demon.co.uk...

I would think the conductive rubber will be able to take 0.5mA no
problem, though the datasheet will say for sure. Consider the surface
area dissipating the power, and compare with a resistor. In general, a
relatively high current like that will make the input more reliable. My
reasoning is thus. If the pullup is as high as 100k, it is easy for RFI
/ ESD to generate a false signal. The extra current drain (0.5mA versus
0.05mA) is only momentary so is not relevant to battery life, if you're
using batteries.
--
Nemo

Thanks Nemo.

I would think so too, especially in this application (the rubber is being
used to short to terminals like a momentary switch and will only have the
current passing through it for a second or less). I can't consult any data
sheet because the rubber is just something I've salvaged off of other
devices.

Thanks