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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.
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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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- 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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- 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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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.
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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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