2. SENSOR
A sensor (also called detector) is a converter that measures a physical
quantity and converts it into a signal which can be read by an observer or
by an electronic instrument. For example, a mercury-in-glass thermometer
converts the measured temperature into expansion and contraction of a
liquid which can be read on a calibrated glass tube.
Sensors are used in everyday objects such as touch-sensitive elevator
buttons (tactile sensor) and lamps which dim or brighten by touching the
base. There are also innumerable applications for sensors of which most
people are never aware. Applications include cars, machines, aerospace,
medicine, manufacturing and robotics.
3.
4. • A metal detector is a device which responds to metal at a
distance.
• Metal detectors are useful for finding metal inclusions
hidden within objects, or metal objects buried underground.
• The simplest form of a metal detector consists of
an oscillator producing an alternating current that passes
through a coil producing an alternating magnetic field.
• If a piece of electrically conductive metal is close to the
coil, currents will be induced in the metal, and this produces
a magnetic field of its own.
5.
6. • This is a simple single chip metal detector circuit based on IC CS209A from the Cherry
Semiconductors.
• A 100uH coil is used to sense the presence of metal.
• The IC CS209A has a built in oscillator circuit and the coil L1 forms a part of its external LC circuit
which determines the frequency of oscillation.
• The inductance of the coil change in the presence of metals and the resultant change in
oscillation is demodulated to create an alarm.
• The LED gives a visual indication too.
• This circuit can sense metals up to a distance of few inches.
7. •Assemble the circuit on a general purpose
PCB.
• The switch S1 can be a slide type ON/OFF
switch.
• The IC must be mounted on a holder.
• The POT R1 can be used to adjust the sensitivity
of the circuit
