IR SENSORS AND ENCODERS. LCDs

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IR SENSORS AND ENCODERS. LCDs

• Timothy Friez
• Class 2

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Outline for Tonight

• Variables overview
• IR Board
• Purpose
• Wiring
• Programming
• Testing
• Using in an Autonomous Program (code sample)
• 10 minute break
• Encoders
• Purpose
• How it works
• Testing and Developing a Program
• Questions

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Why use variables?

• Variables help to simplify your code.
• You can use variables more than once
• When you change a variable once, it changes the
  reference to that variable everywhere.
• Makes your code more english readable.
• Example
• motorport1 100
• motorport2 100
• Or, better
• int speed 100
• motorport1 speed
• motorport2 speed

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Other Advantages of variables

• Any variable declared appears in the global
  variables
• This screen will show the current value of all
  variables.
• Variables can be modified in a program
• example
• int motorspeed 50
• motorspeed motorspeed 2

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Ideas for using variables

• Setting global motor speeds
• int motorspeed 100
• Knowing the condition of your joysticks
• int joystick_x
• joystick_x frcRFp1_y

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Fun with Variables

• Common types of variables
• int integer (whole numbers)
• float floating point number (decimals)
• bool boolean values (true or false)
• Valid uses
• int motorspeed 100
• float pi 3.14159
• bool sensor_check true

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Types of Operators (Boolean)

• 7 primary types of Boolean operators for
  conditional statements
• lt Less Than
• gt Greater Than
• lt Less Than or Equal To
• gt Greater Than or Equal To
• And (both conditions must be true)
• Or (either condition can be true)
• Equal (one condition equals another
  condition)
• ! Not Equal (one condition does not equal
  another)

Values are Boolean, arguments not necessarily.
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IR Sensor Board
Called also the IR board Infrared sensors

• Used for Hybrid mode
• Allows the Human Player to send up to 4 signals
  (but not at the same time)

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IR Sensor Board

• Wiring the board
• 2 positive voltage wires (pin 1 and 2)
• 2 negative voltage wires (pin 3 and 4)
• 4 Signal wires (pins 5, 6, 7, 8)
• These wires go to the Digital I/O port on the
  FRC

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Pin 5 Output 3 Pin 6 Output 2 Pin 7
Output 1 Pin 8 Output 4
Pins 9 and 10 are not used.
Pin 1 and 2 Voltage Pos
Pin 3 and 4 Voltage Ground
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But its not that easy

• You have to hook the signal wires up to the white
  wire of a 3-pin PWM Cable
• Pin 5, Pin 6, Pin 7, and Pin 8 are all signal
  wires
• You then have to hook the ground wire from the IR
  board to the Black wire of the PWM cable to
  complete the electrical circuit!
• Pin 3 and Pin 4 are ground

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Wiring Diagram for IR Board, Robot and 4 digital
sensors
2
3
4
1
IR Board
Pin 4
Pin 8
Pin 1 Pin 2
Pin 7
Pin 6
Pin 3
Pin 5
Robot Voltage
Robot Ground
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So whats that look like?

• A mess, kind of.

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So how do we program it?

• First you have to train the receiver.
• Step 1 Turn power off
• Step 2 Hold button down on IR Board
• Step 3 When LED 1 turns on, press the first
  button.
• If the signal is good, the LED will go off, and
  then back on again.
• Step 4 Press the first button again until LED 1
  goes off once more.
• Step 5 LED 2 will light up repeat with buttons
  2, 3 and 4.
• Once done, all LEDs will turn off, and the IR
  board is programmed.

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How do we ROBOTC program it?

• All 4 of these inputs are treated like digital
  inputs
• Reminder Digital inputs are like touch sensors.
• Code (assume weve put this on port 3)
• frcDigitalIODirectionpio3 dirInput
• Access with frcDigitalIOValuepio3

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Encoders

• Know how many time your drive wheels have gone
  around.
• Need an encoder on each drive motor output.

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Our Encoders? Gear Tooth!

• Each FIRST kit comes with 2 gear tooth encoders.

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How encoders work

• The gear tooth encoder works on a principal
  called the Hall Effect
• Detects differences in magnetic fields and
  produces a result.
• When the sensor reads a tip, it sends a high
  digital value (a 1)
• When the sensor reads a valley, it sends a low
  digital value (a 0)

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How encoders work
Output
1
Gear tooth Sensor
Metal Gear
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How encoders work
Output
0
G.T. Sensor
Metal Gear
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Problems with encoders

• Extremely fragile (look at how tiny it is!)
• Requires 2 cables
• 12 volt power supply
• 5 volt digital signal cable (PWM)
• Must be mounted no further than 2mm away from top
  of gear tooth.
• Not a problem?
• able to be mounted in the 2008 gearboxes directly

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Recommendations for use

• Larger, more robust gear tooth sensor!
• Honeywell 1GT101DC - Hall Effect Gear Tooth
  Sensor
• Digikey.com - 22.29 each shipping
• Advantages
• Only requires one PWM cable
• Rated up to 10000 RPM

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Mounting idea
Almost touching the gear needs to be very close.
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How to program encoders using RobotC?

• Wires into a Digital I/O port.
• Will only tell number of rotations, not direction
• Returns a 1 at a tip, returns a 0 at a valley
• ROBOTC will take care of the counting for you.
• Setup with Motors and Sensors Setup screen
• Access with
• SensorValueencoder1
• Reset to zero with
• SensorValueencoder1 0

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Encoder Go Straight

• Last Weeks Notes
• Use Motors and Sensors Setup to configure our
  encoders
• Clear the encoders before using them
• Program Go straight using encoder feedback
• If left wheel lags behind, slow down right wheel
• If right wheel lags behind, slow down left wheel
• If both wheels are equal, go an equal speed.
• Use Three If statements