A capacitive type sensor circuit using the technology presented in U.S. Patent
3,869,676
During the past few months, I have received quite a few emails about building working
sensors using the information in my patents.  Building the Hall effect sensors is not that
easy because  the correct magnets and Hall Effect sensor ICs are not sold through the
average electronic part stores.  What I will do is to add a few short articles to show how
one can build a linear position sensor or  rotary angle sensor using capacitance measuring
circuit technology. There are several patents that are expired but can still be used to
construct very good position sensors. U.S. Patent 3,869,676 is one such patent.  The
diode-quad bridge technology that was introduced in this patent was used to design
several automotive sensors that were  used starting about 1985. This capactive sensor
technology is still being used today  in rotary, linear, and pressure sensor design. All the
components can be purchased at DigiKey or other electronic suppliers. Several examples
will be presented.   
Click
here to
view U.S.
Patent
3,869,676
on the
USPTO
Website.
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not see
the
patent,
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Data on this and other related pages will be up dated as time permits.  Last up
date:2-3-04
The diode-quad bridge circuit schematic shown below can be used with an Electronic
Workbench Pro electronic circuit simulator program.
The Vcap is a 5 to 55
pF variable capacitor.  If
the Vcap is adjusted
from 5 to 55 pF , the
output voltage will
increase from .5 Volts to
7 Volts. A variable
differential capacitor
assembly can be
designed to build either
a rotary angle or linear
position sensor. As an
FYI, this circuit was
adjusted for an output
voltage of 5 Volts at
+22C. The circuit was
then placed in a freezer
at -40C and the output
voltage droped to 4.76
Volts. The circuit was
then placed in an oven at
+60C and the output
increased to 5.21 Volts.
So, some form of
temperature
compensation may be
required for your
application.

Note: This circuit has
been built and tested
with descrete parts and
simulated with EWB
5.12.
Go To Capacitive Sensor Page 2 of 2  For
additional info