- 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.
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- 5V Capacitance Touch Acitvated 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.
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- 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
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- 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)
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Precision Low Capacitance Meter
NEW
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,...
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