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5V
Capacitance Touch Activated Monetary Switch
This circuit is discussed in more detail in the section on Capacitance
Proximity Switch Technology. The circuit is powered from a standard +5v
supply. It has both a source and sink output that change state whenever a
metal button connected to the circuit is touched. An earth ground reference is
required.
5-Volt Momentary Operation Touch Switch
This simple circuit uses a single IC to form a nice touch switch circuit.
A single transistor forms the remote active switch sensor. Multiple
switches can be wired in parallel. The switch circuit can be located
about 500 feet from the control circuit
Capacitance Type
Liquid Level Monitor This circuit was originally designed to monitor the level of liquid natural gas
in a tank but it can be used to also measure almost any liquid. Two custom insulated
metal tubes form a capacitor plate. The capacitance between the two tubes increases
as the level of the liquid rises. The circuit converts an increase of capacitance
into a positive voltage change. The circuit could be changed to handle almost any
scale factor needed.
Low Value Capacitance
Meter
This circuit was originally designed to measure the volume of fluid inside a medical
syringe. As designed, it produces a zero to 5 volt output, corresponding
to a capacitance change of about 10 picofarads. With a digital voltmeter, at
its output, it can resolve a capacitance change of 0.002 picofarads or 2
femtofarads. (added 12/04)
Precision Low
Capacitance Meter This circuit was originally designed to measure the volume of the fluid inside a
10cc syringe. It used two copper foil strips attached to the outside barrel of
the syringe. The fluid between the two copper strips increases the
capacitance. As the fluid volume decreased, the capacitance also decreased.
With the circuit shown below, it is possible to calibrate the circuit, so the
voltage produced is proportional to the fluid volume inside the syringe. With
the values shown, the circuit produces a 5v DC output,...
Short Range
Reflective Object Sensor
Drawing only 30uA from a 3v supply, this circuit will detect a human finger with a
range of about 1 inch. The sensor uses an inexpensive infrared LED and a
matching photo diode.
