Re: Not-too-conductive material
- From: linnix <me@xxxxxxxxxxxxxxxxxx>
- Date: Thu, 24 Jul 2008 20:50:35 -0700 (PDT)
On Jul 25, 3:50 am, -...@xxxxxxx (Robert Scott) wrote:
I am designing a very cost-sensitive and low-power water level sensor using a
PIC microcontroller. The idea is to run pulse an RC network and measure the
time constant to indicate water level in a reservoir. The resistance is the
effective resistance between two conductive probes partially covered with water.
The trouble is when the water is any more than 2 inches deep, the resistance is
so low that the PIC cannot source that much current directly from a digital
output - not without severely dropping the applied voltage. So I would like the
resistance to be higher. I tried replacing the solid metal probes with very
thin bare wire (wire-wrap size). That helped a little, but the resistance is
still too low. What I would really like is to make the probe out of a material
that has much less conductivity - about 100K for a 6-inch length. I can
consider placing a coating on a plastic substrate, but only if that coating is
rugged enough to stand up to occasional cleanings with a damp rag. Can anyone
suggest a good probe material for this purpose?
Robert Scott
Ypsilanti, Michigan
How about several 10K resistors in series? As the water level rise,
it will short out the lower Rs but keeping the upper Rs.
.
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