L4 — Flowcharts & Obstacle Detection

Lesson 4 of 6

Flowcharts & Obstacle Detection

Designing algorithms visually, then implementing them with IR sensors

Year 9 · Robotics with Edisons

Learning Objectives

1Identify and correctly use the four standard flowchart symbols (terminal, process, decision, I/O)

2Draw a flowchart for an obstacle avoidance algorithm with correct branching

3Implement the algorithm in EdPy using Ed.ReadObstacleDetection() and if/elif/else

Prior Knowledge: Lessons 1–3 — Edison hardware, EdPy movement commands, for loops. Students should be comfortable with the download process.

Prep: Print or display a flowchart symbol reference. Have rulers and pencils ready for drawing flowcharts. Ensure there are small obstacles (books, pencil cases) for testing.

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Key Vocabulary

Flowchart and conditional terminology

🗺️

Flowchart

A visual diagram that shows the steps of an algorithm using standard symbols connected by arrows. Flowcharts are language-independent — they describe WHAT the program does, not HOW it's written in code.

◇

Decision (Selection)

A diamond-shaped flowchart symbol that represents a YES/NO question. It always has two exit paths. In code, this becomes an if statement.

🔴

IR Obstacle Sensor

Edison's front-facing infrared sensors emit light and detect reflections. If an object is within range (~10cm), the sensor reports an obstacle. Read with Ed.ReadObstacleDetection().

🔁

While Loop

A loop that continues as long as a condition is true. while True: runs forever — perfect for a robot that should keep responding until switched off.

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Flowchart Symbols

The four symbols every CS student must know

⬭

Terminal

Start or End of the algorithm. Always oval/rounded rectangle.

▭

Process

An action or instruction. e.g. "Drive Forward", "Turn Left 90°"

◇

Decision

A YES/NO question. Always two exits: Yes path and No path.

▱

Input / Output

Data entering or leaving. e.g. "Read obstacle sensor", "Beep"

Rules students often forget: (1) Decision diamonds ALWAYS have exactly two exits labelled YES and NO. (2) All paths must eventually reach an END terminal — or loop back. (3) Arrows show direction of flow.

Connection to code:
Terminal → start/end of program
Process → a command line (e.g. Ed.Drive)
Decision → if/elif/else
I/O → Ed.ReadObstacleDetection() / Ed.PlayBeep()

Common exam question: Students are given code and asked to draw the corresponding flowchart — or vice versa. Both directions matter.

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Obstacle Detection Code

Mapping the flowchart directly to EdPy

Sensor Values

Value	Meaning
`Ed.OBSTACLE_AHEAD`	Object directly in front
`Ed.OBSTACLE_LEFT`	Object on left side
`Ed.OBSTACLE_RIGHT`	Object on right side
`Ed.OBSTACLE_NONE`	No obstacle detected

Show this live: Hold Edison up and wave your hand in front of it. Open the EdPy serial console to see the sensor value change in real time.

Full Program

import Ed
Ed.EdisonVersion = Ed.V3
Ed.DistanceUnits = Ed.CM
Ed.Tempo = Ed.TEMPO_MEDIUM

reverse_dist = 5
turn_angle = 90
speed = Ed.SPEED_3

while True:
    obstacle = Ed.ReadObstacleDetection()

    if obstacle == Ed.OBSTACLE_AHEAD:
        Ed.Drive(Ed.BACKWARD, Ed.SPEED_5, reverse_dist)
        Ed.TurnLeft(Ed.SPEED_5, turn_angle)
    elif obstacle == Ed.OBSTACLE_LEFT:
        Ed.TurnRight(Ed.SPEED_3, 45)
    elif obstacle == Ed.OBSTACLE_RIGHT:
        Ed.TurnLeft(Ed.SPEED_3, 45)
    else:
        Ed.Drive(Ed.FORWARD, speed, Ed.DISTANCE_UNLIMITED)

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Student Task

Draw the flowchart first — then code it

Direct students to: student.html → L4 Flowcharts & Obstacle Detection. Steps 1–3. Step 3 requires TWO uploads: flowchart photo + code screenshot.

1Step 1: Draw a flowchart for a simple obstacle avoidance algorithm (forward → check → reverse + turn if obstacle → loop). Upload photo.

2Step 2: Study the obstacle detection values. Type and test the full program from Slide 4. Screenshot the code.

3Step 3: Draw an improved flowchart matching the full code (inc. left/right cases). Enhance the code (beep on detection + random turn). Two uploads required.

🥉 Bronze

Correct flowchart symbols for a 2-path algorithm. Working obstacle avoidance code that reverses and turns.

🥈 Silver

+ Flowchart includes all 4 cases (ahead, left, right, none). Code includes beep on detection. Comments in code.

🥇 Gold

+ Random turn direction using Ed.GetRandomNumber(1,2) — flowchart updated to show random branch.

Physical setup: Place a few books or pencil cases on desks as obstacles. Students test their Edison navigating around them. Clear a 60×60cm area per pair minimum.

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Plenary

Consolidate and preview Lesson 5

Exit Ticket — Peer Discussion (2 min)

"The else branch in our obstacle code runs Ed.Drive with Ed.DISTANCE_UNLIMITED. If we removed the while True loop, would the robot still avoid obstacles indefinitely? Why or why not?"

✅ Today we covered

Four standard flowchart symbols
Decision diamonds — always two exits
Ed.ReadObstacleDetection() values
while True: for continuous behaviour
if / elif / else conditional logic

⏭ Next Lesson

Lesson 5: Light, Sound & the Robot Claw

Edison responds to line tracking sensors and clap detection — then we attach the EdBuild robot claw to combine movement and gripper control.

Exit ticket answer: Without while True, the if/elif/else only checks the sensor once. The robot would make one decision then stop — not continuous avoidance.