Download EE462 Principles of Mobile Robots Autumn 2000

Sensors I
Lecture is based on material from Robotic Explorations: A Hands-on Introduction to Engineering, Fred Martin, Prentice Hall, 2001.
Gas Sensor
Gyro
Accelerometer
Pendulum Resistive
Tilt Sensors
Metal Detector
Piezo Bend Sensor
Gieger-Muller
Radiation Sensor
Pyroelectric Detector
UV Detector
Resistive Bend Sensors
Digital Infrared Ranging
CDS Cell
Resistive Light Sensor
Pressure Switch
Miniature Polaroid Sensor
Limit Switch
Touch Switch
Mechanical Tilt Sensors
IR Pin
Diode
IR Sensor w/lens
Thyristor
Magnetic Sensor
IR Reflection
Sensor
Magnetic Reed Switch
IR Amplifier Sensor
Hall Effect
Magnetic Field
Sensors
Polaroid Sensor Board
IRDA Transceiver
Lite-On IR
Remote Receiver
Radio Shack
Remote Receiver
IR Modulator
Receiver
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Solar Cell
Compass
Compass
Piezo Ultrasonic Transducers
How about we add a color sensor?
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Objective
To be able to discriminate between objects
of different colors. In this example, objects
are painted different colors: red, green,
blue.
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BRAINSTORMING
How can we determine color?????
Objects possess color because they reflect light
of a particular wavelength and absorb light of
other wavelengths.
For example, green objects reflect light with a
wavelength of approximately 520 nm; other
wavelengths are absorbed. A green object
photographed in red light would appear almost
black.
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BRAINSTORMING
• Our plan will be to illuminate an object with red light and
measure the amount of reflected light.
• We will then repeat using a source of green light.
• Finally, we will illuminate the object with blue light.
• When the color of the light used to illuminate the object and the
color of the object match we get a large value from the sensor;
when the colors do not match we get a small value.
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Red Light Emitting Diode (LED)
• Stanley H-300L ultra-bright red LEDs
(647 nm)
• Made from GaAlAs.
• 3000 mcd with IF = 20 mA and VF = 1.8V
• Digi-Key P/N: 404-1104-ND
• Maximum IF is 50 mA.
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Green Light Emitting Diode (LED)
• Kingbright WP7104VGC1A ultra-bright
green LEDs (520 nm)
• Made from InGaN.
• 3000 mcd with IF = 20 mA and VF = 4.0V
• Digi-Key P/N: 754-1259-ND
• Maximum IF is 30 mA.
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Blue Light Emitting Diode (LED)
• Panasonic LNG992CFBW ultra-bright blue
LEDs (470 nm)
• Made from ?.
• 1500 mcd with IF = 20 mA and VF = 3.5V
• Digi-Key P/N: P465-ND
• Maximum IF is ? mA.
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How do we drive an LED?
+VDD
Connect to 5 VDC pin or
motor port (7.2 VDC)
R1
R2
C1
LED
R3
2N2222A
Connect to digital port bit
set_digital_output_value(port_number, value)
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Light Sensor Circuits
There are many ways to assemble light sensor elements
into sensor devices that can be employed on a robot.
A CdS photocell is a very simple transducer that one can
use for transforming changes in light intensity into
changes in resistance.
Optical Spectrum
How does a CdS photocell work?
CdS is a semiconductor. When photons on light strike the
semiconductor, electrons are excited into the conduction band,
leaving behinds holes (vacancies in the valence band). The
more intense the light, the more carriers which are created and
hence the more conductive (less resistive) is the photocell.
PDVP-5003
Light Sensor Circuits
Single Photocell Circuit
•If your photocell easily floods from ambient
room light, then the next order of business is to
build an optical shield to limit the amount of
ambient light that is able to fall on the sensor
Photocell Sensors with Light Shields
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Using a CdS Cell to Sense Light
+5 VDC
RCdS
To 10-bit ADC input
Make sure you disable the 15K pull-up resistor.
R
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Calibration
Adjust the potentiometer in the each of the LED
circuits so the ADC values are approximately the
same for each of the three colored (R, G, B) LEDs
when their light is reflected from a white surface (an
inch or so away from the sensor).
Record the ADC value when light is reflected from a
red, then a green, and finally from a blue surface. Do
this for each of the three colored LEDs.
Using some type of “similarity measure” you should
be able to determine the color of an unknown object.
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Color Sensor
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FORCE SENSOR
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Resistance vs Force
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Force Threshold Switch
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Force/Pressure Measuring Circuit
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