Report back

Students make a patrol robot that follows the line and sends a radio alert to a base station when it is blocked, using a true/false variable so it alerts once, then build a snake spotter.

Robotics challenges · Talk · about 50 minutes · Open the student lesson

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

Slides Download Present from the browser, or export to PowerPoint or PDF.
Worksheet Download Print the student copy; the Teacher edition has the answers.

Students will be able to

I can make a robot send a radio message when its sensor detects something.
I can use a true/false variable so a message is sent once, not every time round.
I can give one program two roles (robot and base) with a variable.

Timing

Predict and Run 10 min · Investigate 10 min · Modify 12 min · Make 15 min · Real robot 3 min (optional)

Before class

This is the assistance strand: lesson 5's line following plus lesson 7's radio, in the other direction. The robot works on its own and reports back. Two new ideas:

Send once. forever runs many times a second, so an alert inside it would be sent again every time round while the box is there (Noah's patrol). A true/false variable, alerted, remembers that the robot has already told; it goes back to false when the way is clear. Students met true/false variables in the Foundations challenge (no cheating in the reaction timer).
Roles. Because the simulator runs the same program on both micro:bits, a role variable decides what each one does: every micro:bit starts as a robot; A+B makes it the base, which stops and listens.

Messages are words (send string, on radio received receivedString). On real hardware the base can be a bare micro:bit (untested whether the robot start block errors without a robot; if so, give the base a copy without it).

Running the lesson

Predict: most expect one beep; some expect continuous beeping. Both are worth hearing before Noah's patrol.
Run: press A+B on the second micro:bit first. Then block the first robot with a box on the line.
Investigate: trace alerted on the board: false → true (send) → stays true (no send) → false when clear.
Modify: 'clear' is sent once for the same reason: only when alerted was true.
Make: the snake spotter turns round, so the box ends up behind it: it sends once without needing alerted. Ask why.
Real robot (optional): range and walls matter; discuss what a real inspection robot should do out of range.

The hard part (on purpose)

An alert in forever is sent every time round unless a flag remembers it. Ask what stops the robot sending again.

When students get stuck

What you will see	A question to ask	The fix
The base never reacts.	Did you press A+B on the base? Is the box on the other robot's line?	Make one micro:bit the base first, then block the other robot.
The base beeps again and again.	What stops the robot sending every time round?	Use alerted: send only if not alerted, then set alerted to true.
'clear' is sent all the time.	Is the send inside if alerted?	Send clear only when alerted is true, then set it to false.

Answers to the checks

Predict: Press A+B on the second micro:bit (the base). Then drag a box onto the line in front of the first robot. What does the base do?
It shows an X and beeps once. The robot sends 'blocked' and sets alerted to true, so it does not send again until the way is clear.
Tell once: What is the variable alerted for?
It remembers that the robot has already sent 'blocked', so it only sends once until the way is clear
alerted becomes true when the alert is sent. While the box stays, forever sees alerted is true and does not send again. When the way is clear, alerted goes back to false, ready for next time.
Noah's patrol: Noah's base beeps again and again, very fast, while the box is in front of his robot. Why?
His robot sends 'blocked' every time forever runs while the box is there, because nothing remembers it has already told
forever runs many times a second. While the box is close, Noah's if is true every time, so it sends every time. A variable like alerted lets it send once.

Solutions

One possible solution for each task. Other correct programs are fine.

Modify › All clear

Show as code

function followLine () {
    if (robot.detectLine(RobotLineDetector.Left) && robot.detectLine(RobotLineDetector.Right)) {
        robot.motorTank(40, 40)
    } else if (robot.detectLine(RobotLineDetector.Left)) {
        robot.motorTank(10, 40)
    } else if (robot.detectLine(RobotLineDetector.Right)) {
        robot.motorTank(40, 10)
    } else {
        robot.motorStop()
    }
}
input.onButtonPressed(Button.AB, function () {
    role = "base"
    robot.motorStop()
    basic.showString("B")
})
radio.onReceivedString(function (receivedString) {
    if (role == "base") {
        if (receivedString == "clear") {
            basic.showIcon(IconNames.Yes)
        } else {
            basic.showIcon(IconNames.No)
            music.play(music.tonePlayable(880, music.beat(BeatFraction.Whole)), music.PlaybackMode.InBackground)
        }
    }
})
let alerted = false
let role = ""
robot.elecfreaksCuteBot.start()
radio.setGroup(1)
role = "robot"
basic.forever(function () {
    if (role == "robot") {
        if (robot.obstacleDistance() < 15) {
            robot.motorStop()
            if (!(alerted)) {
                radio.sendString("blocked")
                alerted = true
            }
        } else {
            if (alerted) {
                radio.sendString("clear")
            }
            alerted = false
            followLine()
        }
    }
})

Modify › Count the alerts

Show as code

function followLine () {
    if (robot.detectLine(RobotLineDetector.Left) && robot.detectLine(RobotLineDetector.Right)) {
        robot.motorTank(40, 40)
    } else if (robot.detectLine(RobotLineDetector.Left)) {
        robot.motorTank(10, 40)
    } else if (robot.detectLine(RobotLineDetector.Right)) {
        robot.motorTank(40, 10)
    } else {
        robot.motorStop()
    }
}
input.onButtonPressed(Button.AB, function () {
    role = "base"
    robot.motorStop()
    basic.showString("B")
})
radio.onReceivedString(function (receivedString) {
    if (role == "base") {
        if (receivedString == "clear") {
            basic.showIcon(IconNames.Yes)
        } else {
            alerts += 1
            basic.showNumber(alerts)
            music.play(music.tonePlayable(880, music.beat(BeatFraction.Whole)), music.PlaybackMode.InBackground)
        }
    }
})
let alerts = 0
let alerted = false
let role = ""
robot.elecfreaksCuteBot.start()
radio.setGroup(1)
role = "robot"
basic.forever(function () {
    if (role == "robot") {
        if (robot.obstacleDistance() < 15) {
            robot.motorStop()
            if (!(alerted)) {
                radio.sendString("blocked")
                alerted = true
            }
        } else {
            if (alerted) {
                radio.sendString("clear")
            }
            alerted = false
            followLine()
        }
    }
})

Make

Show as code

function followLine () {
    if (robot.detectLine(RobotLineDetector.Left) && robot.detectLine(RobotLineDetector.Right)) {
        robot.motorTank(40, 40)
    } else if (robot.detectLine(RobotLineDetector.Left)) {
        robot.motorTank(10, 40)
    } else if (robot.detectLine(RobotLineDetector.Right)) {
        robot.motorTank(40, 10)
    } else {
        robot.motorStop()
    }
}
input.onButtonPressed(Button.AB, function () {
    role = "base"
    robot.motorStop()
    basic.showString("B")
})
radio.onReceivedString(function (receivedString) {
    if (role == "base" && receivedString == "snake") {
        basic.showIcon(IconNames.Snake)
        music.play(music.stringPlayable("C5 A C5 A C5 A - - ", 240), music.PlaybackMode.InBackground)
    }
})
let role = ""
robot.elecfreaksCuteBot.start()
radio.setGroup(1)
role = "robot"
basic.forever(function () {
    if (role == "robot") {
        if (robot.obstacleDistance() < 15) {
            robot.motorStop()
            robot.setColor(0xff0000)
            radio.sendString("snake")
            basic.pause(2000)
            robot.motorTank(50, -50, 1200)
            robot.setColor(0x000000)
        } else {
            followLine()
        }
    }
})

Stretch and support

Stretch: Two-way: the base sends 'go' with A, and a robot that has stopped waits for 'go' before it carries on (a mode variable from lesson 6).

Support: Give the base side complete; students add the robot's alert with the alerted variable.

Exit ticket

Why does the robot need the alerted variable?

forever checks many times a second. Without alerted it would send the alert every time while the box is there; alerted remembers it has already sent, so it sends once.

What each step is for

Investigate: forever keeps checking, so an alert in forever would be sent again every time round. A true/false variable remembers that the robot has already told, so it tells once.
Modify: The robot and the base agree on a few message words; each new word needs a sender and a meaning.

Where it leads

Next: the challenge unit. Showcase (performance) and Patrol and alert (assistance) put the course together. Real-world links: pipeline and warehouse inspection robots, wildlife cameras that send an alert, smoke alarms that report to a phone.