Today we are going to Discuss about sensors .
1.What is a sensor?
2. Types of sensors
3. How to use it?
4. Where to use it?
WHAT IS A SENSOR….?
• A sensor is a device that measures a physical
quantity and converts it into a signal which can be
read by an observer or by an instrument.
• Sensors are used in everyday objects such as touch-
sensitive elevator buttons (tactile sensor) and lamps
which dim or brighten by touching the base.
• Applications include cars, machines, aerospace,
medicine, manufacturing and robotics.
TYPES OF SENSORS
• IR SENSOR
• SOUND SENSOR
• TEMPERATURE SENSOR
• IR sensor works on the principle of emitting IR
rays and receiving the reflected ray by a
receiver (Photo Diode).
• IR source (LED) is used in forward bias.
• IR Receiver (Photodiode) is used in reverse
IR Sensor circuit
• A Comparator is a device which compares two
voltages or currents and switches its output to
indicate which is larger.
• Comparator is an Op-amp.
PIN DIAGRAM LM 358
LIGHT Sensor Circuit
• The LM35 is an integrated circuit sensor that
can be used to measure temperature with an
electrical output proportional to the
temperature (in o
• The scale factor is 10mV/o
TIMER 555 IC
The 555 Timer IC is an integrated
circuit (chip) implementing a variety
of timer and multivibrator applications.
• In this mode, the 555 functions as a "one-
• Applications include timers, missing pulse
detection, bouncefree switches, touch
switches, frequency divider, capacitance
measurement, pulse-width modulation
CIRCUIT DIAGRAM IN MONOSTABLE MODE
• The pulse begins when the 555 timer receives a
• The width of the pulse is determined by the time
constant of an RC network, which consists of
a capacitor (C1) and a resistor (R1).
• The pulse width can be lengthened or shortened
to the need of the specific application by
adjusting the values of R and C.
• In bistable mode, the 555 timer acts as a basic flip-flop.
• The trigger and reset inputs (pins 2 and 4 respectively on a
555) are held high via pull-up resisters while the threshold
input (pin 6) is simply grounded.
• Thus configured, pulling the trigger momentarily to ground
acts as a 'set' and transitions the output pin (pin 3) to Vcc
• Pulling the reset input to ground acts as a 'reset' and
transitions the output pin to ground (low state).
• No capacitors are required in a bistable configuration
• Pin 8 (Vcc) is, of course, tied to Vcc while pin 1 (Gnd) is
• Pins 5 and 7 (control and discharge) are left floating.
• In Astable mode, the '555 timer ' puts out a
continuous stream of rectangular pulses having a
• Resistor R1 is connected between VCC and the discharge
pin (pin 7) and another resistor (R2) is connected
between the discharge pin (pin 7), and the trigger (pin
2) and threshold (pin 6) pins that share a common
• Hence the capacitor is charged through R1 and R2, and
discharged only through R2.
Triggering of IC 555 using Sound Sensor
• In the above circuit we are triggering the 555
timer by applying voltage produced by sound.
• This voltage when generated pass through the
capacitor which works as a filter.
• This filtered voltage is then fed to transistor
which is inverting the voltage and also
• And hence creating a negative triggering pulse.