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Comparators, Op-amp and sensors

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by

Ruchita Kachhap

on 25 August 2013

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Transcript of Comparators, Op-amp and sensors

In this class
1. Comparators
2. Operational Amplifiers
3. Sensors
i. LED-LDR
ii. IR LED-Photodiode
Comparators
Operations Amplifiers
Op-amps as comparators
Sensors
LED
LDR
Obstacle sensing using LED-LDR
IR-LED
IR-Photo diode
Obstacle sensor using IR LED , Photo diode and Op Amp
Pull-Up
* Light Dependent Resistor
* LDR’s resistance is inversely proportional to the intensity of light.
That is more the light, lesser the resistance
* Light Emitting Diode
* Generally used with LDR to complete the sensor module.
* Acts as a source of light.
* The reflected light falling on LDR helps us to judge about the surface it has fallen on.
* Can be used to differentiate dark (less reflective) and light surfaces.
* Can be used to detect close (more reflective) and distant surfaces.
* This is the IR receiver. Detects Infra red radiations.
Works similar to LED-LDR sensor. The only major difference is that it detects IR radiation and not visible light.
* Emits IR radiations.
* Used in combination with IR receiver to complete the IR sensor.
V = A (V - V )
input+
input-
out
* A comparator is used to compare two voltages.
V > V
If,
+
-
V
out
= Floating
V < V
+
-
V
out
= 0
* It amplifies the difference in the input voltages.
* Sensors are the components of robot which help them to obtain input from the environment.
* Pull-up resistor is used to ensure that floating input always reads high (1) .
Lets see this in case of a comparator.
* Reference voltage is set using the potentiometer at the - input terminal.
* Amplification gain (A) can be set using resistors.
* Op amp ICs include LM324 , IC 741 etc.
* Comparator ICs includes IC 339 (contains 4 comparators), LM319 etc.
IC 339
* Amplification gain, A can be as high as 100,000
LM 324
* Simplest use of Op amp is as a comparator.
Vref
Vin
Vcc +
Vcc -
* A floating voltage is an undefined open voltage.
V > V
+
-
V
out
= 1
V < V
+
-
V
out
= 0
* Comparator ICs contain the pull-up resistor so, there the output pin will read high for the corresponding cases.
Full transcript