Stateflow chart creation in Simulink - Mini Project: Build & Apply

Stateflow Chart Creation

📖 Scenario: You are designing a simple traffic light controller using a Stateflow chart in Simulink. The traffic light has three states: Red, Green, and Yellow. The controller will switch states in a fixed sequence to manage traffic flow safely.

🎯 Goal: Create a Stateflow chart with the three states Red, Green, and Yellow. Configure the transitions so the traffic light cycles through these states in order: Red → Green → Yellow → Red.

📋 What You'll Learn

Create a Stateflow chart named TrafficLight inside a Simulink model.

Add three states named Red, Green, and Yellow.

Set the initial state to Red.

Add transitions from Red to Green, Green to Yellow, and Yellow to Red.

Use a simple condition or event to trigger each transition.

💡 Why This Matters

🌍 Real World

Traffic light controllers are common examples of state machines used in real-world traffic management systems to ensure safe and efficient vehicle flow.

💼 Career

Understanding Stateflow charts is important for engineers working in embedded systems, automotive software, and control system design.

1

Create a Simulink model and add a Stateflow chart

Open Simulink and create a new model. Add a Stateflow chart block to the model and name it TrafficLight.

Simulink

% Open Simulink and create a new model
% Add a Stateflow chart block named TrafficLight
% Your code here

Hint

Use new_system to create a model and add_block to add a Stateflow chart block.

2

Add three states named Red, Green, and Yellow

Inside the TrafficLight Stateflow chart, add three states named Red, Green, and Yellow. Set the initial state to Red.

Simulink

% Add three states named Red, Green, and Yellow inside the TrafficLight chart
% Set the initial state to Red
% Your code here

Hint

Use sfroot to get the chart and addState to add states. Use set('InitialState', ...) to set the starting state.

3

Add transitions between the states

Add transitions from Red to Green, from Green to Yellow, and from Yellow to Red. Use a simple condition true to trigger each transition.

Simulink

% Add transitions from Red to Green, Green to Yellow, and Yellow to Red
% Use condition 'true' for each transition
% Your code here

Hint

Use addTransition to connect states and set the Condition property to 'true' to trigger transitions immediately.

4

Display the Stateflow chart and verify transitions

Print the names of the states and their outgoing transitions with conditions to verify the Stateflow chart setup.

Simulink

% Print the states and their outgoing transitions with conditions
% Your code here

Hint

Use fprintf to print the state names and their outgoing transitions with conditions.

Practice

1. What is the main purpose of creating a Stateflow chart in Simulink?

easy

A. To design graphical user interfaces

B. To model systems with different states and transitions

C. To perform numerical calculations on data arrays

D. To create 3D animations

Solution

1. Step 1: Understand the role of Stateflow charts

   Stateflow charts are used to represent systems that have multiple states and rules for moving between those states.

2. Step 2: Compare with other options

   Options A, B, and D describe tasks unrelated to Stateflow charts, which focus on state-based system modeling.

3. Final Answer:

   To model systems with different states and transitions -> Option B

4. Quick Check:

   Stateflow charts = state and transition modeling [OK]

Hint: Stateflow = states + transitions modeling [OK]

Common Mistakes:

• Confusing Stateflow with data processing blocks
• Thinking Stateflow creates GUIs
• Assuming Stateflow is for animations

2. Which of the following is the correct way to create a new state in a Stateflow chart?

easy

A. Drag a 'State' block from the Simulink library browser

B. Double-click the Simulink block to add a state

C. Use the MATLAB command addstate() in the command window

D. Right-click inside the chart and select 'Add State'

Solution

1. Step 1: Identify how to add states in Stateflow

   In Stateflow, you add states by right-clicking inside the chart and choosing 'Add State' from the menu.

2. Step 2: Evaluate other options

   Double-clicking a Simulink block or dragging blocks from Simulink library does not add states in Stateflow. The addstate() command does not exist.

3. Final Answer:

   Right-click inside the chart and select 'Add State' -> Option D

4. Quick Check:

   Add state = right-click menu [OK]

Hint: Right-click inside chart to add states [OK]

Common Mistakes:

• Trying to add states from Simulink library
• Using nonexistent MATLAB commands
• Double-clicking blocks expecting to add states

3. Consider a Stateflow chart with two states: Idle and Active. The transition from Idle to Active occurs when start == 1. If start is 0 initially and then changes to 1, what will be the active state after simulation?

medium

A. Active

B. Idle

C. Both Idle and Active

D. No active state

Solution

1. Step 1: Understand the transition condition

   The chart starts in Idle. When start == 1, it transitions to Active.

2. Step 2: Analyze the simulation behavior

   Initially, start is 0, so the chart stays in Idle. When start changes to 1, the transition triggers, moving the chart to Active.

3. Final Answer:

   Active -> Option A

4. Quick Check:

   start=1 triggers transition to Active [OK]

Hint: Transition triggers when condition true [OK]

Common Mistakes:

• Assuming state changes before condition is true
• Thinking both states can be active simultaneously
• Ignoring transition conditions

4. You created a Stateflow chart but the simulation does not switch states as expected. Which of the following is a likely cause?

medium

A. The chart has too many states

B. The Simulink model is not saved

C. Transition condition is missing or incorrect

D. The MATLAB version is outdated

Solution

1. Step 1: Identify common reasons for no state switching

   If transitions do not have correct conditions, the chart will not move between states.

2. Step 2: Evaluate other options

   Having many states does not prevent switching. Not saving the model or MATLAB version usually does not cause this specific issue.

3. Final Answer:

   Transition condition is missing or incorrect -> Option C

4. Quick Check:

   Missing transition condition blocks state change [OK]

Hint: Check transition conditions first [OK]

Common Mistakes:

• Blaming number of states for no transitions
• Ignoring transition conditions
• Assuming saving fixes simulation logic

5. You want to create a Stateflow chart that models a traffic light with states Red, Green, and Yellow. The light should cycle through these states every 5 seconds. Which approach correctly implements this behavior?

hard

A. Create states for Red, Green, Yellow with transitions triggered by a timer event every 5 seconds

B. Create one state with a variable counting seconds and use if-else inside it

C. Use Simulink blocks only without Stateflow to model timing

D. Create states but transitions happen manually by user input

Solution

1. Step 1: Understand traffic light cycle requirements

   The traffic light cycles through states automatically every 5 seconds, so timed transitions are needed.

2. Step 2: Evaluate implementation options

   Create states for Red, Green, Yellow with transitions triggered by a timer event every 5 seconds uses states and timer-triggered transitions, which fits the requirement. Create one state with a variable counting seconds and use if-else inside it uses one state and if-else, which is less clear and harder to manage. Use Simulink blocks only without Stateflow to model timing ignores Stateflow, losing state logic. Create states but transitions happen manually by user input requires manual input, not automatic cycling.

3. Final Answer:

   Create states for Red, Green, Yellow with transitions triggered by a timer event every 5 seconds -> Option A

4. Quick Check:

   Timed transitions cycle states automatically [OK]

Hint: Use timer events for automatic state cycling [OK]

Common Mistakes:

• Using manual input instead of timer events
• Trying to do all logic in one state
• Ignoring Stateflow for state-based timing