Sensors / Detectors: Capacitance Sensors

Sensors / Detectors: Capacitance Sensors
Sensors / Detectors -- Main Page
Last Updated on: Friday, October 16, 2009 03:42 AM

Circuits Designed by Dave Johnson, P.E. :

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

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 NEW
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.

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

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. ….(designed by David A. Johnson)

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. ….(designed by David A. Johnson)

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

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

AN-829: Environmental Compensation on the AD7142: The Effects of Temperature & Humidity on Capacitance Sensors - AN-829 Analog Devices Application Notes (app note added 6/06)

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

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

Audio Acquires the Write touch - 02/20/03 EDN-Design Ideas:.....(design idea added 6/03)

Build this add on Capacitance Meter - This simple add-on capacitance meter has been specially designed to help you identify capacitors from 1p to 10u. There has always been a problem identifying capacitors, due ….(schematic / circuit added 05/07)

Capacitance Meter - This project is more complex than the others described earlier. However, when finished, you will have an instrument capable of measuring all but the largest capacitors used in radio circuits. Unlike variable resistors, most variable capacitors are not marked with their values. As well, the markings of capacitors from salvaged equipment often rub off....(electronic design idea added 09/08)

Capacitance meter (a.van.waarde) - Every home constructor should own at least two pieces of test equipment: a digital (or analog) multimeter and a simple frequency counter. Most digital multimeters can measure capacitance, but the capacitance range is rather limited…(schematic / circuit added 05/07)

Capacitance meter (Colin Mitchell) - This simple add-on capacitance meter has been specially designed to help you identify capacitors from 1p to 10u….(schematic / circuit added 05/07)

Capacitance Meter (Elm-chan) - This is a simple capacitance meter which can measure capacitance value easy. There are some measurement methods for capacitance, at one time the capacitance was measured with a impedance bridge or a dip meter….(circuit added 9/04)

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. ….(designed by David A. Johnson)

Capacitive Sensor likes Parasitics - 09/24/98 EDN-Design Ideas: (design idea added 3/03)

Capacitive touch switch uses CPLD - 05/29/08 EDN-Design Ideas: Using an Altera MAX IIZ CPLD, you can implement a touch-switch decoder with no external components.....(design idea added 09/08)

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

Digital Capacitance Meter (Elm-chan) - This is a simple capacitance meter which can measure capacitance value easy. There are some measurement methods for capacitance, at one time the capacitance was measured with a impedance bridge or a dip meter….(circuit added 9/04)

Dual Comparators Stabilize Proximity Detector - 02/16/98 EDN-Design Ideas: (design idea added 3/03)

Environmental Compensation on the AD7142 - AN-829 Analog Devices Application Notes (app note 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. (added 2/03) (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 .... (added 6/06)

Infra-red Liquid Level Detector - Useful for liquids level detection and proximity devices Up to50 cm. range, optional relay operation (added 4/05)

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) ….(designed by David A. Johnson)

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

Measure open circuited cables using a multimeter - 09/26/02 EDN-Design Ideas: 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.....(design idea added 1/05)

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

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

Precision capacitive Sensorinterface suits miniature instruments - 07/24/08 EDN-Design Ideas: A pair of one-shots develops a voltage proportional to the value of a capacitive sensor and transmits these readings via a LVDS interface.....(design idea added 09/08)

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,... ….(designed by David A. Johnson)

RS232C Link Monitors Animal Activity - 11/06/97 EDN-Design Ideas: (design idea added 3/03)

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. ….(designed by David A. Johnson)

Solve Low frequency cutoff problems in capacitive sensors - 11/28/02 EDN-Design Ideas: 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.....(design idea added 1/05)

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 (Tony van Roon) - (schematic / circuit added 10/02)

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