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Battery Powers Capacitance Switch
Using a unique differential time comparison technique this capacitance
switch can detect a change of just one picofarad.
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 ....
Also see
Completed Doorknob Alarm 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.
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.….
