program bumper & limit switches in autonomous mode

Available at: www.etcurr.com Lesson 3.1 – Program Bumper & Limit Switches in Autonomous Mode

Program bumper & limit switches in autonomous mode



Performance Objective: Given the components of a VEX robotics design system program a bumper switch [and limit switch] in autonomous mode to have the robot back up for two seconds after coming in contact with a wall, then terminate the program.

Enabling Objectives: define autonomous programming and its purpose explain the difference between inputs and outputs explain the difference between digital and analog

sensors describe a variable and its purpose in programming



Enabling Objectives: describe the types of conditional expressions used in

VEX programming describe the difference between a bumper and limit

switch draw a flow chart for using a bumper switch verify a bumper switch program a bumper switch utilize Competition Switch Simulator


Autonomous Programming

Autonomous means that you program the robot to do something on its own

You do not control the robot with the Joystick in autonomous mode

The purpose of autonomous programming is to have a self-controlled robot


Inputs & Outputs (I/O)

In autonomous programming you work with inputs and outputs

An input in the case of VEX is an input device

An input device provides data and control signals to the microcontroller

The input devices used with VEX are sensors


Inputs & Outputs (I/O)

An output is an electrical signal from the microcontroller used to drive an output device

An output is usually observable, such as a motor running

Some sensors utilize both inputs and outputs to perform their function


Digital & Analog

Inputs and outputs will be either digital or analog

Digital I/O are discrete, meaning on or off; true or false; 1 or 0

1 or 0 is used within a programming language to express a digital value

Think of a light switch, it is either on or off (true or false, 1 or 0) there is no in between


Digital & Analog

Analog I/O are continuous, meaning the value can range from a minimum value to a maximum value, with an infinite number of possibilities in between

Think of a light that is connected to a dimmer switch, the light can be off, or it can vary in brightness up to its maximum brightness level


Variables

In order to use a sensor, you must first define a variable in the software

A variable is a symbolic name given to some known or unknown quantity or value (memory address)

In VEX programming the variable name can be only a single string of letters

When using a digital sensor, the input value (1 or 0) will be stored in the variable name


Variables

The most common variable type that we will use in VEX programming is an integer (int)

An int allows you to store the data type value of the sensor in the variable name

You can then recall the variable name throughout a program


Conditional Expressions

Conditional expressions allow a program to make a decision based on certain information

Common examples of conditional expressions are: while loops and if-then-else statements


While loops

While loops perform a task while a statement is true or not false

Recall from operator mode: while 1 is true, perform tank mode


If-then-else Statements

These statements test a condition, if the condition meets the criteria then perform a task, else-if a different condition is met, then perform a different task


Bumper versus limit switch The two switches perform the same

function The main difference between a

bumper switch and a limit switch is the mechanism used to receive the signal

A bumper switch uses a button A limit switch uses an arm When the button or arm is pressed,

the same signal is sent to the microcontroller from the sensors


Programming a bumper switch versus a limit switch

This lesson will walk you through the steps to program a bumper switch

To program the two switches the same steps are followed

The sensors do use different function blocks in easyC


Flow Charting

When programming it is helpful to draw a flow chart of a program before you actually write the code

The action allows you to see how the program will operate and get a clear picture of how the code should flow

When flow charting, there are specific blocks or symbols that are used


Flow Chart Symbols

Start and End Symbols Arrows Input/Output Conditional Decision

Start

Bumper Switch Input

End

Decision A

Decision B

Yes

No


Flow Charting

When flow charting use the symbols to plan out your program

Add in the actions you want to perform


Flow Charting

This flow chart goes through the following process:

Check bumper switch If bumper switch is

no, repeat process If bumper switch is B,

then end the program

Start

Bumper Switch Input

End

Decision A

Decision B

Yes

No


Flow chart a Bumper switch

Flow chart a bumper switch and motors on the activity sheet

If the button is not pushed, move the robot forward

If the button is pushed, stop the robot for 1 second, backup for 2 seconds

Show your instructor before continuing


Verifying a Sensor

Begin by checking the port which the sensor is plugged into

Configure the motors and Sensor(s) in the main program tab

Start a New Competition Project After starting a new project you will see five tabs, click

on the Operator Control tab


Verifying a Sensor

Notice the while loop has already been inserted

Insert a driving mode (tank or joystick) function for two motors into the existing while loop

Set the motor numbers according to your configuration


Verifying a Sensor

Before downloading the code, be sure to prop your robot up so that the wheels are not touching a surface

Build and Download the new code Close the Loader window Under Tools, open the On-line Window Enable the On-line Window


On-line WindowEnable/Disable

Test motors

Verify Sensors

Configura-tion set by you


Verify Sensor with On-line Window

Recall which port the bumper switch is plugged into Look at that port in the digital I/O box Now push the bumper switch Notice the value is 1 when the bumper is not pushed

and 0 when pushed


Program a Bumper Switch in Autonomous mode

Close the On-line Window Click on the Main tab Double click on the Globals

icon Define a new global variable

as an integer (int) variable for the bumper switch

Name it Click on the Autonomous

tab Insert while loop where

1==1



Insert a bumper switch input from the function block tree into the while loop

Select the appropriate Digital input port

Select the variable where to send (Retrieve to:) the value from the sensor (this is what you named the variable you created)

Click ok



Insert an If statement from the Program Flow menu

Write the If Statement

If bumper(insert your variable name) ==0



Refer to your flow chart to insert the proper functions into the if statement

If bumper == 0, it means that the button is pushed You want the robot to stop for 1 second and then backup for

2 seconds, and then stop Use a Wait function to pause for a certain amount of time The wait command counts in milliseconds, remember 1

second = 1000 milliseconds Try to write the above statements into your If statement After you have attempted to write the code, refer to the

next slide for the solution



Stops the motors Waits 1 second Reverses motors Waits 2 seconds

(allows motors to stay in reverse for two seconds)

Stops motors



After the robot runs in reverse, we want the program to terminate (stop running)

To do this enter a Return function from the Program Flow menu

This Return command sends the robot back to the main code window, where the autonomous program is told to end by default



Refer to your flow chart If the bumper switch is not

pushed, we want the robot to continue to moved forward

To do this enter an Else Statement below the If statement

In this Else statement insert the proper motor modules to move the robot forward



You want the while loop to continue to run through the else statement when the bumper switch is not pushed in order to keep the robot moving forward


Testing Your Autonomous Code

Build and Download your code Leave the IFI Loader Window open At the bottom is the Competition Switch Simulator This simulator allows you to test you autonomous

code


Testing Your Autonomous Code

First click Disable, this stops the program from running Next, click on Autonomous Then click Enable, this will run your autonomous

program You can repeat this process to retest you program


Program Terminated

Congratulations, your robots program should terminate with the bumper switch

Show your success to your instructor

If your program is not functioning properly, read through the lesson again to see if you can find the faults, if you still cannot get your robot to operate properly, ask your instructor for assistance

program bumper & limit switches in autonomous mode

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