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Sensor Interfacing
Why Robots need Sensors
The first primitive of robotics is “Sense”.
A robot senses its environment by means of sensors and transducers
Different Types of Sensing
Touch Vision Listening Feel ( Pressure,Temperature, Humidity) Smell
Similar to human beings Robots Can sense all these with help of different types of sensors
Different Sensors
For vision a robot Uses 1. Camera2. Light and Infrared Sensors
Sound Sensors
The Common Sound Sensors are1. Microphone2. Ultrasound sensors
Temperature and Humidity
Thermistor Humidity Sensor
GAS SENSOR
Some More Sensors
Heartbeat Sensor
Passive Infrared Sensor
Sensor & Transducers
Transducer is a device which converts electrical signals to other kind of
energy and Vice-Versa.
Sensor is an assembly which contains some transducer and some
electronic processing circuitry
Resistive Transducers
Resistive Transducers are those, whose resistance varies with the change of the external signal.
Example – LDR, Thermistor
Commonly used Sensors in Robotics
Mainly Optical sensors are used in robotics in student level, because they are cheap and easily available
Commonly Used Optical sensors Are
1. Light Dependent Resistors2. Infrared Sensors
Light Dependent Resistor
An LDR has a resistance that varies according to the amount of visible light that falls on it. More the incident light, less the resistance. This is known as a negative resistance co-efficient.
How the Light Sensor works
A LDR Sensor array by THE ARELAB.
Here LDRs and High intensity LEDs are placed side by side to make them suitable for light sensing
Reflection type LDR sensor
LEDLDR
Why Light Sensors are Used
A Very common objective in the modern competition robots is to follow a white line on a black background
Making the Potential Divider
+
LD
R
RES
ISTIV
E
DIV
IDER
FIX
ED
RES
ISTA
NC
E
• The LDR gives change of the resistance with the variation of incident light. We have placed the LDR in one arm of a potential divider.
• Now, if the resistance of the LDR varies, the output voltage of the potential divider also changes
What to do next
It is clear that the output of the potential divider is an analog voltage. But Microcontroller does not accept the analog voltage. So we need to convert the analog voltage to digital before we feed it to the microcontroller.
For this conversion we can use1. Comparators2. ADCs
Comparators
-
COMPARATOR LM339
+
V+
V-
V0 V0 = High when V+ > V-V0 = Low when V+ < V-
Comparators
-
COMPARATOR LM339
+
V(LDR)
V( REF)
V0
V(LDR)= LDR output VoltageV( REF) = To be set by a potentiometer
Setting the V(Ref)
Rotating the potentiometer 22 times give the full swipe of the resistance range.
Connection of LDRs
FIX
ED
RES
ISTA
NC
E
RES
ISTIV
E
DIV
IDER
+ 5VPOTENTIOMETER
OUTPUT
V
Ω
+
LD
R-
COMPARATOR LM339+
5V
Checking the Resistance
On white Line – More light Reflects, so LDR resistance goes down.
On Black Background – Less light reflects, So LDR resistance goes up.
Function of the Comparator
V+
V-
V+ > V-
0 V
HIGH
-
+
Function of Comparator
V+
V-
V+ < V-
0 V
LOW
-
+
Function of Comparator
V+
V-
V+ > V-
5 V
HIGH
+ 5V
-
+
Drawbacks of LDR
Does not give precise measurements for position calculations.
Ambient interference degrades performance
Infrared Sensors
Infra-Red emitter sends IR pulses
Position calculation is done through intensity of reflected light received by the detector.
Ambient interference is negligible
How to position IR sensor
0.5cm
EMITTER
DETECTOR
IR connections
+ +
+
100 OHMS
10 K OHMS
IR SENSOR ARRAY
Black Wire – Output Voltage
Red Wire - +5V
Brown Wire - Gnd
Thank You
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