Sensors

1. SENSORS

2. Today we are going to Discuss about sensors .
1.What is a sensor?
2. Types of sensors
.IR sensor
.Sound sensor
.Temperature sensor
3. How to use it?
4. Where to use it?

3. 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.

4. TYPES OF SENSORS
•IR SENSOR
•SOUND SENSOR
•TEMPERATURE SENSOR

5. IR SENSOR

6. WORKING
•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
bias.

7. IR Sensor circuit

8. VOLTAGE COMPARATOR
•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.

9. PIN DIAGRAM LM 358

10. LIGHT Sensor Circuit

11. TEMPERATURE SENSOR

12. Contd....
•The LM35 is an integrated circuit sensor that
can be used to measure temperature with an
electrical output proportional to the
temperature (in
o
C).
•The scale factor is 10mV/
o
C .

13. TIMER 555 IC

14. The 555 Timer IC is an integrated
circuit (chip) implementing a variety
of timer and multivibrator applications.

15. PIN DIAGRAM

16. OPERATING MODES
•MONOSTABLE MODE
•BISTABLE MODE
•ASTABLE MODE

17. Monostable mode
•In this mode, the 555 functions as a "one-
shot"
•Applications include timers, missing pulse
detection, bouncefree switches, touch
switches, frequency divider, capacitance
measurement, pulse-width modulation
(PWM) etc

18. CIRCUIT DIAGRAM IN MONOSTABLE MODE

19. Contd....
•The pulse begins when the 555 timer receives a
trigger signal.

•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.


T = 1.1 X R1 X C1

21. Bistable Mode
•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
(high state).
•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
grounded.
• Pins 5 and 7 (control and discharge) are left floating.

22. Astable mode
• In Astable mode, the '555 timer ' puts out a
continuous stream of rectangular pulses having a
specified frequency.
• Resistor R
1
is connected between V
CC
and the discharge
pin (pin 7) and another resistor (R
2) is connected
between the discharge pin (pin 7), and the trigger (pin
2) and threshold (pin 6) pins that share a common
node.
•Hence the capacitor is charged through R
1
and R
2
, and
discharged only through R
2.

23. Triggering of IC 555 using Sound Sensor

25. Contd....
•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
amplifying it.
•And hence creating a negative triggering pulse.

26. Thank You…