Pressure dependent Resistor 1500mA current? (HELP)

Hi everyone....
So here is the challenge. How can we implement a current limitation
into our application.
We have a small high end flashlight which is using a rotary knob in
the back. The knob can be rotated, the rotation (uses a thread) results
in the knob making contact with the battery -
in which case the flashlight turns on. Now we noticed that when I just
slightly turn the knob, that there seems to be a mechanical current
limitation - where the light turns on but isnt very bright - this is
probably because the current is limited physically we assume.
However this is way too sensitive. We are basically looking for sort of
a pressure-sensitive current limiter we can put onto the tip (of the
knob) which contacts the battery - which will limit the current that
can flow from the battery to the knob - depending on how much pressure
the knob applies to this sensor - which will contact the battery.
The battery has a voltage between 2.5V and 4.5V. The maximum current
draw out of the battery is about 1500mA. The pressure sensor should
either allow full current with max. pressure or very little to no
current with no pressure.
Size constraints. The solution should fit onto the tip of where the
threaded knob part makes contact with the battery which is a circle
with a 7mm diameter. The height of the solution can be up to 50mm
(however smaller is preferred). However the distance travel of the knob
from max pressure to no pressure should only be a couple of mm.
I hope that makes sense. If not ask.
This is the closest thing I was able to find myself:
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The problem it can only take 5mA.
Ideally we are looking for a round 7mm diameter sandwich - where the
more the sandwich or part is squeezed together the more current can
flow from the
bottom to the top of the sandwich. Max Current 1500mA (if your solution
is a bit larger let us know maybe we can accomodate something larger).
Anyone have an idea whether there is such a part out there - or how to
build something small?
Reply to
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Its probably due to your switch making an initial high resistance connection. This can be fixed by designing a switch with a 'snap action', (i.e. mechanical hysteresis). If that's what you want.
What about in-between? Are you trying to eliminate the intermediate dim (high restsiance) mode or actually incorporate a dimmer? If its tha latter, there are far better (more energy efficient) means of doing it.
50mm = about 2 inches
That's pretty big. I can fit a high quality rotary switch or a PWM dimmer in less space.
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Paul Hovnanian P.E.

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