Sensors / Detectors: Capacitance Sensors


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Sensors / Detectors: Capacitance Sensors
Last Updated on: Tuesday, April 22, 2008 03:50 PM

Sensors / Detectors -- Main Page

Circuits Designed by Dave Johnson, P.E. :

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 ACTIVATED MOMENTARY 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)

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

AN1014: Measuring Small Changes in Capacitive Sensors: Microchip Application Note - Published 8-Dec-05 (added 2/06)

AN1016A: Detecting Small Capacitive Sensors using the MCP6291 and PIC16F690 Devices: Microchip Application Note - Published 8-Dec-05 (added 2/06)

AN-829: Environmental Compensation on the AD7142: The Effects of Temperature and Humidity on Capacitance Sensors: AN-829 - Analog Devices Application Notes (Circuit / schematic design added 6/06)

AN-833: Using the AD7142 and a Capacitive Sensor to Develop a Single-Push Digital Shutter Button: AN-833 - Analog Devices Application Notes (added 2/06)

AN9 Zetex Variable Capacitance Diodes: Zetec Semiconductors - Applications Notes - An introduction to the basic theory, an explanation of the important parameters, and typical applications are described within this note. An overview is also provided for the Zetex range of variable capacitance diodes. (added 2/06)

Audio Acquires the Write touch: 02/20/03 EDN-Design Ideas / (added 11/05)

Capacitance Meter #1: (Circuit added 9/04)

Capacitance Meter #2: (added 8/03)

Capacitance meter that connects to multimeter: (Electronic circuit added 4/05)

Capacitive Sensor likes Parasitics: 09/24/98 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)

Detecting Small Capacitive Sensors using the MCP6291 and PIC16F690 Devices: Microchip Application Note - Published 8-Dec-05 (added 2/06)

Dual Comparators Stabilize Proximity Detector: 02/16/98 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)

Environmental Compensation on the AD7142: AN-829 - Analog Devices Application Notes (Circuit / schematic design added 6/06)

Femto Capacitance Meter: This meter measures into the low femtofarad area. Measuring in the femto area allows the smallest capacitors to be measured with precision. Such capacitors are commonly used to compensate for input and stray capacitance in amplifiers. (circuit / schematic added 2/03) (Electronic circuit added 5/02)

Infra-Red (IR) Beam Alarm/ Proximity Detector: This circuit can be used as an Infrared beam barrier as well as a proximity detector. The circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets. The receiver consists of a 555 timer IC working as an oscillator .... (Circuit / schematic design added 6/06)

Infrared Level Detector for Liquid Level Detection and Proximity Detection: Useful for liquids level detection and proximity devices Up to50 cm. range, optional relay operation (Circuit / schematic design added 6/06)

Mains-operated Capacitive Sensor: Easily adjustable, high sensitivity circuit. Minimum parts counting (circuit design added 3/05)

Measure open circuited cables using a multimeter: 09/26/02 EDN Design Ideas / (added 1/05) You can use a multimeter with capacitance-measurement capability to measure the length of wire or cable to an open circuit. The capacitance of a pair of wires (or a wire to a shield) is directly proportional to the length of the wire. If you know the capacitance per foot of wire, then you can calculate how far it is to the open circuit....

Measuring Small Changes in Capacitive Sensors: Microchip Application Note - Published 8-Dec-05 (added 2/06)

Negative Impedance Improves Capacitive Sensors: 03/30/95 EDN-Design Ideas / (added 03/03)

RS-232C Link Monitors Animal Activity: 11/06/97 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)

Solve Low frequency cutoff problems in capacitive sensors: 11/28/02 EDN Design Ideas / (added 1/05) One of the first problems a capacitive-sensor analog designer must face is the low-frequency cutoff. Theoretically, you must fulfill just one simple requirement: a sufficiently large input resistance of the preamplifier's first stage. In practice, however, many problems lurk behind the seemingly straightforward design rules....

Stud Sensor Automatic : This thing is a very neat capacitive sensor. For you europeans, this little gem is used in north america mostly for detecting wooden beams behind drywall. (added 2/05)

Touch Activated Alarm: (added 10/02)

Using the AD7142 and a Capacitive Sensor to Develop a Single-Push Digital Shutter Button: AN-833 - Analog Devices Application Notes (added 2/06)

Zetex Variable Capacitance Diodes: Zetec Semiconductors - Applications Notes - An introduction to the basic theory, an explanation of the important parameters, and typical applications are described within this note. An overview is also provided for the Zetex range of variable capacitance diodes. (added 2/06)