IR SENSORS AND ENCODERS. LCDs Timothy Friez Class # 2

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

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: motor[port1] = 100; motor[port2] = 100; Or, better… int speed = 100; motor[port1] = speed; motor[port2] = speed;

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;

Ideas for using variables Setting global motor speeds –int motorspeed = 100; Knowing the condition of your joysticks –int joystick_x; –joystick_x = frcRF[p1_y];

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 = ; –bool sensor_check = true;

Types of Operators (Boolean) 7 primary types of Boolean operators for conditional statements < Less Than > Greater Than <= Less Than or Equal To >= 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.

IR Sensor Board Used for “Hybrid” mode Allows the Human Player to send up to 4 signals (but not at the same time…) Called also the IR board = Infrared sensors

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

Pin 1 and 2: Voltage Pos Pin 3 and 4: Voltage Ground Pin 5 – Output #3 Pin 6 – Output #2 Pin 7 – Output #1 Pin 8 – Output #4 Pins 9 and 10 are not used.

But it’s 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

Wiring Diagram for IR Board, Robot and 4 digital sensors IR Board Robot Voltage + Pin 1 Pin 2 Robot Ground Pin 3 Pin Pin 5 Pin 6 Pin 7 Pin 8

So what’s that look like? A mess, kind of.

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.

How do we ROBOTC program it? All 4 of these inputs are treated like digital inputsAll 4 of these inputs are treated like digital inputs –Reminder: Digital inputs are like touch sensors. Code: (assume we’ve put this on port 3) –frcDigitalIODirection[pio3] = dirInput; –Access with frcDigitalIOValue[pio3]

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

Our Encoders? Gear Tooth! Each FIRST kit comes with 2 gear tooth encoders.

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”)

How encoders work Gear tooth Sensor Output: 1 Metal Gear

How encoders work G.T. Sensor Metal Gear Output: 0

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

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 RPM

Mounting idea Almost touching the gear… needs to be very close.

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 –SensorValue[encoder1] Reset to zero with –SensorValue[encoder1] = 0;

Encoder – Go Straight Last Week’s 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