Download robots and eyes v2

MAKING YOUR ROBOTS SEE
Building and Testing Photosensitive
eyes
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1
Building Photosensitive Eyes
Parts
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1.
Two Photo-Resistors
2.
Two 0.1µF Capacitors
3.
Two 220Ω Resistors
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Circuit Building
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Concepts
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Resistors
Reduces the flow of current
Photo-resistor
 Resistance value varies with change in lighting
condition
 Resistance is less in the presence of more light
and more in the absence of less light
Capacitor
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Stores energy
Controls the reaction of the photo-sensor
Programming to Measure
Resistance
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RC Time
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Time it take the lower plate of the capacitor to discharge from 5 to
1.4 V. BASIC Stamp I/O pin’s threshold voltage = 1.4v.
voltage depends on R × C, the RC time constant, Tau.
When voltage > 1.4 V, register input = 1, when voltage < 1.4 V,
register input = 0.
Resistor and Capacitor are constant. Photo-resistor value changes
based on light, so the voltage changes.
rctime command measures how long it takes for the voltage to fall
from 5 to 1.4 V.
RC time varies according to the formula:
RC Time Measurements
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Controlling your Robot Based on
RC time
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Deadband
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A threshold that indicates different lighting (or color) conditions
seen by the resistors
Allows you tell the robot what direction to turn
Following a Black Stripe
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If deadband criteria is not met, just go forward
If deadband criteria is met, then check to see what direction to go
Example: If RC time for left wheel is greater than RC time for right
wheel
 Which wheel sees a darker color?
 What should the robot do?
Controlling your Robot Based on
RC time
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Avoiding a Black Stripe
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If deadband criteria is not met, just go forward
If deadband criteria is met, then check to see what direction to go
Example: If RC time for left wheel is greater than RC time for right
wheel
 Which wheel sees a darker color?
 What should the robot do?