| 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.
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- 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.
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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.
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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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- 120VAC Touch Switch
This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load.
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- 240VAC Touch Switch
This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load.
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- 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
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- 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.
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- 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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