Detecting Other Conditions

These custom functions use the push button, IR line sensors, or accelerometer:

  • checkButton() — check if button is pressed in order to "start" or "pause" robot

  • pauseRobot() — pause until button is pressed before performing next step in task

  • checkDropOff() — check for surface drop-off (e.g., stair step, etc.)

  • checkUpsideDown() — check if robot is upside down (pitch or roll greater than 90°)

  • checkBump() — check if robot has been bumped

You can also use the millis() method as a clock to set a timer for a while() loop to perform a continuous task (such as: avoiding a line, etc.) for a certain duration of time.

while() loop timer

You can make your robot perform a task for a certain duration of time, similar to setting a timer. This is useful for behaviors that must be continuously called within a loop (such as: drive straight, check bumpers, avoid collision, avoid line, check drop-off, etc.).

Arduino has a millis() method which acts like a clock. Your robot's microcontroller keeps track of how many milliseconds have elapsed since your robot app first started. Your desired timer duration is then used to set an end time for the task.

A while() loop is used to perform the task continuously until the timer runs out (i.e., until the current time exceeds the end time). In this example code, the timer is set for 30 seconds, but you can change the timer to whatever duration you need.

Add this code within another custom function, such as task1(), etc.

// get current time (in milliseconds)
unsigned long time = millis();
// set end time (in milliseconds)
unsigned long duration = 30000; // change if necessary
unsigned long endTime = time + duration;
// while current time is less than end time, loop performs task
while (time < endTime) {
// add code to perform continuous task (avoid line, etc.)
time = millis(); // check current time again
}
// time's up
motors.stop();

ADD CODE TO WHILE LOOP: You need to add code statement(s) within the while() loop to perform the continuous task(s).

checkButton()

A custom function named checkButton() checks whether the built-in D12 button is being pressed. If the button is pressed, the function will toggle the value of a global variable named started from false to true (or vice versa). The function will also provide feedback by blinking the built-in D13 LED light and producing a beep with the speaker.

The checkButton() function uses a RedBotButton object to read the button. Create this object as part of your global variables before the setup() function:

RedBotButton button;

The checkButton() function uses global variables that store the pin numbers for the LED and speaker and that track whether the robot is "started" (true) or "paused" (false). Add this code before the setup() function:

int LED = 13;
int speaker = 9;
bool started = false;

Set the pin modes for the LED and speaker by adding this code within the setup() function:

pinMode(LED, OUTPUT);
pinMode(speaker, OUTPUT);

Add the checkButton() custom function after the loop() function:

void checkButton() {
if (button.read() == true) {
// reverse value of started
started = !started;
// beep and blink as feedback
digitalWrite(LED, HIGH);
tone(speaker, 2000);
delay(200);
digitalWrite(LED, LOW);
noTone(speaker);
delay(200);
}
}

You can add this code within the loop() function to perform different actions based on whether the robot is "started" (started == true) or "paused":

checkButton();
if (started == true) {
// add code to perform when "started"
}
else {
// add code to perform when "paused"
}

ADD CODE: You need to add code to perform different actions based on whether the robot is "started" (e.g., drive, etc.) or "paused" (e.g., stop motors, etc.).

ONE BUTTON LIBRARY: Another option is to use the OneButton library to detect different types of button presses (single-press, double-press, or long-press).

pauseRobot()

A custom function named pauseRobot() can be used to add "pauses" in a robot's task. The robot will wait until the built-in D12 button is pressed before performing the next step in the task. This could be useful in a robot task demonstration.

For example, you could add a "pause" for a simulated step in a task. The robot will "pause" while you complete or explain the simulated step. Once you press the button, the robot will continue with the next step in the task.

This "pause" is created using a while() loop that keeps repeating itself until the button is pressed. The while() loop contains a short delay before it checks the button again.

The pauseRobot() function uses a RedBotButton object to read the button. Create this object as part of your global variables before the setup() function:

RedBotButton button;

The pauseRobot() function will produce a "beep" as an alert when the robot is paused and produce another beep as feedback once the button is pressed. This uses a global variable that stores the pin number for the speaker. Add this code before the setup() function:

int speaker = 9;

Set the pin mode for the speaker by adding this code within the setup() function:

pinMode(speaker, OUTPUT);

Add the pauseRobot() custom function after the loop() function:

void pauseRobot() {
motors.stop(); // make sure robot is stopped
tone(speaker, 2000, 200); // beep as alert
while (button.read() == false) delay(10); // wait until button pressed
tone(speaker, 2000, 200); // beep as feedback
delay(200); // allow button to be released
}

Then you can call the pauseRobot() function within the loop() function or within a custom function whenever you want the robot to pause its task until the button is pressed.

For example, the code below shows how the pauseRobot() function could be used within a task to add a "pause" for a simulated step. The robot will pause until the button is pressed.

// drive to destination
driveDistance(36);
pivotAngle(90);
driveDistance(24);
// pause for simulated step
pauseRobot();
// drive back to start
pivotAngle(180);
driveDistance(24);
pivotAngle(-90);
driveDistance(36);

checkDropOff()

A custom function named checkDropOff() uses the IR sensors to allow your robot to detect a surface drop-off (such as: the edge of a table, a stair step leading down, a hole in the surface, etc.).

Even a small increase in the distance between the IR sensors and the surface (as little as 0.25 inch) will greatly reduce the amount of reflected IR light that is detected.

When a surface drop-off is detected, the motors will be braked. You can add code to perform additional actions (such as backing up, changing direction, etc.).

In order to work, the checkDropOff() function must be continuously called by the loop() function (or continuously called by a loop within another function).

The checkDropOff() function requires these objects as part of your global variables before the setup() function:

RedBotMotors motors;
RedBotSensor leftLine(A3);
RedBotSensor centerLine(A6);
RedBotSensor rightLine(A7);

Add the checkDropOff() custom function after the loop() function:

void checkDropOff() {
// IR threshold indicating drop-off (table edge, hole, etc.)
int dropOff = 950; // adjust value if necessary
// get IR sensor readings
int leftSensor = leftLine.read();
int centerSensor = centerLine.read();
int rightSensor = rightLine.read();
// see if any IR sensors detect drop-off
if (leftSensor > dropOff || centerSensor > dropOff || rightSensor > dropOff) {
// add code to perform (brake, reverse, change direction, etc.)
motors.brake();
}
}

ADD CODE TO FUNCTION: You need to add code within the checkDropOff() function to perform actions (brake, back up, etc.) when a drop-off is detected.

checkUpsideDown()

A custom function named checkUpsideDown() uses the accelerometer to detect whether the robot's pitch or roll is greater than 90° (which indicates the robot has flipped over).

When the checkUpsideDown() function is called, it will return a bool value (boolean) of either true or false. Your app will typically store this value in a local variable, and then do something with the value.

For example, this code statement declares a local variable named upsideDown to store the bool value returned by calling the checkUpsideDown() function:

bool upsideDown = checkUpsideDown();

In order to work, the checkUpsideDown() function must be continuously called by the loop() function (or continuously called by a loop within another function).

The checkUpsideDown() function requires these objects as part of your global variables before the setup() function:

RedBotMotors motors;
RedBotAccel accel;

Add the checkUpsideDown() custom function after the loop() function:

bool checkUpsideDown() {
// if robot is upside-down, returns value of true
// otherwise returns value of false
// get new accelerometer data
accel.read();
// get absolute values for pitch and roll
float pitch = abs(accel.angleXZ);
float roll = abs(accel.angleYZ);
// see if pitch or roll is greater than 90 degrees & return value
if (pitch > 90 || roll > 90) return true;
else return false;
}

Add this code within the loop() function (if you are using the started variable, add this code within the if statement, so it will be performed when started is true) or within a loop in a custom function:

bool upsideDown = checkUpsideDown();
if (upsideDown == true) {
// add code to perform special actions: brake, distress signal, etc.
motors.brake();
}
else {
// add code to perform normal actions: drive, turn, etc.
}

ADD CODE: You need to add code to perform special actions (brake, etc.) when the robot is upside-down, as well as to perform normal actions (drive, etc.) when the robot isn't upside-down.

checkBump()

A custom function named checkBump() uses the accelerometer to detect when the robot is physically bumped as the result of a collision or other force.

The accelerometer detects a bump by checking for a "pulse" acceleration.

The checkBump() function requires these objects as part of your global variables before the setup() function:

RedBotMotors motors;
RedBotAccel accel;

To enable bump detection, add this code statement within the setup() function:

accel.enableBump();

Add the checkBump() custom function after the loop() function:

void checkBump() {
bool bump = accel.checkBump();
if (bump == true) {
// add code to perform special actions: brake, distress signal, etc.
motors.brake();
}
}

ADD CODE TO FUNCTION: You need to add code within the checkBump() function to perform actions (brake, distress signal, etc.) when a bump occurs.