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Sensors / Detectors: Capacitance Sensors Circuits
Designed by David A. Johnson, P.E.

Last Updated on: Monday, April 21, 2008 04:19 AM

Master Category List - Dave's Circuits
 
  • 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.
  • 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.
  • 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
  • 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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