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Sensors / Detectors: Capacitance / Touch Switch Circuits
Capacitance Switches:   #'s       A-R         T-Z

Sensors / Detectors Main Page
Last Updated on:
Saturday, August 30, 2014 10:27 AM

Circuits Designed by Dave Johnson, P.E. :
  • 1.5V TOUCH ACTIVATED SWITCH)
    A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad.

  • 12V TOUCH SWITCH EXCITER CIRCUIT
    This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits.  It can support a cable length of about 2500 feet.  A typical remote switch circuit is also shown as well as a receiver circuit for those switches.
  • 120VAC Touch Switch
    This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load.
  • 240VAC Touch Switch
    This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load. 
  • 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.

  • 5V 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.
  • DOORKNOB ALARM
    Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms. A metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood door. Anyone grabbing the knob from the outside is detected by the electrical capacitance change that occurs from the human hand contact between the knob and the box. Almost all of the commercial devices sold use a more expensive and power consuming radio frequency circuit approach to detect the capacitance change. But, a very inexpensive and micro power technique can also work. This circuit schematic should dramatically reduce the cost of the device and allows it to operate for many years from one set of batteries.

Also see Completed Project  by Matthew C. Ruschmann

  • FINGER TOUCH ACTIVATED SWITCH
    It does not get any easier if you want a solid state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch is not desired.
  • HIGH POWER TOUCH SWITCH EXCITER CIRCUIT
    If you have hundreds of touch switches that need an excitation signal, then this circuit is what you need.  Its 20KHz 20v peak to peak output signal can supply up to 3 watts of touch switch excitation power.

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1.5v Touch Activated Switch -  A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad. . [Designed by David A. Johnson]
101 Seconds Duration On Switch with Touch Control -  This is a touch control switch which keeps the circuit on about 100 seconds after touching the plate connected to the 2 numbered pin. At the end of this time duration, relay releases and the circuit gets to off position. The impedance of the trigger input of the 555 timer IC is very high and the inductive voltage on the human body is enough to trigger it. The circuit works based on this principle. You can use a piece of metal as a plate. The circuit can be used in toy circuits, buzzers or any project that is suitable. You can adjust the duration time by changing the R1 and C1 values. .(Circuit design added 11/08)
120vac Touch Switch -  This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load.... [Designed by David A. Johnson]
12v Touch Switch Exciter Circuit -  This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits.  It can support a cable length of about 2500 feet.  A typical remote switch circuit is also shown as well as a receiver circuit for those switches.... [Designed by David A. Johnson]
240VAC Touch Switch -  This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load.... [Designed by David A. Johnson]
3v Capacitance Proximity Switch -  This circuit was designed to provide a touch activated switch function without an external power supply.  It draws so little power that a single 3v battery will operate the circuit for many years.  It is discussed in more detail in the section on Capacitance Proximity Switch Technology. (Note link is off site) . [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]
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]

Capacitance Switches:   #'s       A-R         T-Z
 


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