SENSORS

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?

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

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.

IR Sensor circuit

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.

PIN DIAGRAM LM 358

LIGHT Sensor Circuit

TEMPERATURE SENSOR

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

TIMER 555 IC The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multi-vibrator applications.

PIN DIAGRAM

OPERATING MODES MONOSTABLE MODE BISTABLE MODE ASTABLE MODE

Mono-stable 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

CIRCUIT DIAGRAM IN MONOSTABLE MODE

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

Bi-stable Mode In bi-stable 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 bi-stable 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.

A-stable mode In A-stable mode, the '555 timer ' puts out a continuous stream of rectangular pulses having a specified frequency. 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 node. Hence the capacitor is charged through R1 and R2, and discharged only through R2.

Triggering of IC 555 using Sound Sensor

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.

Thank You…