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;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 = 3.14159;– 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 BoardIR 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 PosPin 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 4

4123

Pin 5

Pin 6Pin 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 All 4 of these inputs are treated like digital inputsdigital inputs– Reminder: Digital inputs are like touch

sensors.

• Code: (assume we’ve put this on port 3)– frcDigitalIODirection[pio3] = dirInput;

– Access with frcDigitalIOValue[pio3]

EncodersEncoders• 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 able to be mounted in the 2008 gearboxes

directlydirectly

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

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