Signal routing (Mux, Demux, Switch) in Simulink - Mini Project: Build & Apply

Signal Routing with Mux, Demux, and Switch in Simulink

📖 Scenario: You are working on a simple signal routing system in Simulink. You want to combine multiple signals, select one signal based on a control input, and then split the combined signal back into individual signals.

🎯 Goal: Build a Simulink model that uses a Mux block to combine three input signals, a Switch block to select one signal based on a control input, and a Demux block to split the output signal back into separate signals.

📋 What You'll Learn

Create three constant input signals with values 1, 2, and 3.

Use a Mux block to combine the three signals into one vector signal.

Add a control signal to select which input passes through the Switch block.

Use a Demux block to split the output of the Switch block back into individual signals.

Display the final output signals using Display blocks.

💡 Why This Matters

🌍 Real World

Signal routing is essential in control systems, communication systems, and data processing to manage multiple data streams efficiently.

💼 Career

Understanding how to use Mux, Demux, and Switch blocks in Simulink is important for engineers working in embedded systems, automation, and signal processing.

1

Create three constant input signals

Create three Constant blocks named const1, const2, and const3 with values 1, 2, and 3 respectively.

Simulink

# Add three Constant blocks with values 1, 2, and 3
# Name them const1, const2, and const3

Hint

Use three Constant blocks and set their Value parameters to 1, 2, and 3.

2

Add a Mux block to combine signals

Add a Mux block named mux1 and connect the outputs of const1, const2, and const3 to its inputs.

Simulink

% Create three Constant blocks with specified values
% Add a Mux block named mux1 and connect const1, const2, const3 outputs to mux1 inputs
# Your code here

Hint

Use a Mux block with 3 inputs and connect each constant output to one input.

3

Add a Switch block with control input

Add a Switch block named switch1. Create a Constant block named control with value 2. Connect the output of mux1 to the first input of switch1 and the control block to the control input of switch1.

Simulink

% Create a Constant block named control with value 2
% Add a Switch block named switch1
% Connect mux1 output to switch1 first input
% Connect control output to switch1 control input
# Your code here

Hint

Use a Switch block and a control Constant block with value 2. Connect mux output to switch input and control to switch control input.

4

Add Demux block and display outputs

Add a Demux block named demux1 with 3 outputs. Connect the output of switch1 to demux1. Add three Display blocks named disp1, disp2, and disp3. Connect each output of demux1 to one Display block. Finally, run the simulation and print the output values of the displays.

Simulink

% Add Demux block named demux1 with 3 outputs
% Connect switch1 output to demux1 input
% Add three Display blocks named disp1, disp2, disp3
% Connect each demux1 output to one Display block
% Run simulation and print display outputs
# Your code here

Hint

Use a Demux block with 3 outputs, connect the switch output to it, then connect each output to a Display block. Run the simulation and print the display values.

Practice

1. What is the main purpose of a Mux block in Simulink signal routing?

easy

A. To select one signal from multiple inputs based on a condition

B. To split one signal into multiple signals

C. To combine multiple signals into one signal

D. To delay a signal by a fixed time

Solution

1. Step 1: Understand the function of Mux

   A Mux block takes several input signals and combines them into a single output signal vector.

2. Step 2: Compare with other blocks

   Demux splits signals, Switch selects signals, and Delay delays signals. Only Mux combines signals.

3. Final Answer:

   To combine multiple signals into one signal -> Option C

4. Quick Check:

   Mux combines signals = C [OK]

Hint: Mux combines signals; Demux splits; Switch selects [OK]

Common Mistakes:

• Confusing Mux with Demux
• Thinking Switch combines signals
• Assuming Mux delays signals

2. Which of the following is the correct way to connect a Demux block in Simulink?

easy

A. One input signal, multiple output signals

B. Multiple input signals, one output signal

C. Multiple input signals, multiple output signals

D. One input signal, one output signal

Solution

1. Step 1: Recall Demux block behavior

   Demux takes a single input vector signal and splits it into multiple output signals.

2. Step 2: Match with options

   Only One input signal, multiple output signals describes one input and multiple outputs, which fits Demux.

3. Final Answer:

   One input signal, multiple output signals -> Option A

4. Quick Check:

   Demux splits one input to many outputs = A [OK]

Hint: Demux splits one input into many outputs [OK]

Common Mistakes:

• Reversing input and output roles
• Confusing Demux with Mux
• Assuming Demux has multiple inputs

3. Given the following Simulink model snippet:

Input1 = 3;
Input2 = 7;
Input3 = 5;
mux_out = Mux([Input1, Input2, Input3]);
demux_out = Demux(mux_out);

What will be the value of demux_out[1] (the second output of Demux)?

medium

A. 3

B. Error: Index out of range

C. 5

D. 7

Solution

1. Step 1: Understand Mux output

   Mux combines inputs [3, 7, 5] into a vector: mux_out = [3, 7, 5].

2. Step 2: Understand Demux output

   Demux splits mux_out back into separate outputs: demux_out[0]=3, demux_out[1]=7, demux_out[2]=5.

3. Final Answer:

   7 -> Option D

4. Quick Check:

   Second Demux output = 7 [OK]

Hint: Mux packs inputs; Demux unpacks in same order [OK]

Common Mistakes:

• Mixing up output indices (0-based vs 1-based)
• Assuming Demux changes order
• Expecting error due to indexing

4. You have a Switch block with inputs: Input1=10, Input2=20, and a control signal Control=0.
If the Switch block is configured to output Input1 when Control is 0, but the output is always 20, what is the likely error?

medium

A. Control signal logic is inverted or misconfigured

B. Input1 and Input2 are swapped in the block

C. Switch block cannot handle numeric inputs

D. Control signal is not connected

Solution

1. Step 1: Analyze expected Switch behavior

   With Control=0, output should be Input1=10, but output is 20 (Input2).

2. Step 2: Identify cause of wrong output

   This suggests the control logic is inverted or misconfigured, causing the block to select Input2 when Control=0.

3. Final Answer:

   Control signal logic is inverted or misconfigured -> Option A

4. Quick Check:

   Wrong output means control logic error = D [OK]

Hint: Check control logic polarity if Switch output is unexpected [OK]

Common Mistakes:

• Assuming inputs are swapped without checking control
• Thinking Switch can't handle numbers
• Ignoring control signal connection

5. You want to build a Simulink model that takes three sensor signals and selects one to output based on a control signal (0, 1, or 2). Which combination of blocks correctly achieves this?

hard

A. Use a Demux to split sensors, then multiple Switch blocks to select output

B. Use a Mux to combine sensors, then a Multiport Switch block with control signal to select output

C. Use a Mux to combine sensors, then a Switch block with control signal to select output

D. Use three Switch blocks each connected to one sensor, controlled by the same control signal

Solution

1. Step 1: Understand the requirement

   We need to select one of three sensor signals based on a control signal with values 0, 1, or 2.

2. Step 2: Evaluate block combinations

   A Multiport Switch block can select one input from many based on control. Combining sensors with Mux then using Multiport Switch fits this need.

3. Step 3: Why other options fail

   Use a Mux to combine sensors, then a Switch block with control signal to select output uses a simple Switch which only selects between two inputs, not three. Use a Demux to split sensors, then multiple Switch blocks to select output uses Demux incorrectly. Use three Switch blocks each connected to one sensor, controlled by the same control signal uses multiple Switches but control signal can't select one cleanly.

4. Final Answer:

   Use a Mux to combine sensors, then a Multiport Switch block with control signal to select output -> Option B

5. Quick Check:

   Multiport Switch selects among many inputs = A [OK]

Hint: Use Multiport Switch for multiple input selection [OK]

Common Mistakes:

• Using simple Switch for more than two inputs
• Misusing Demux for selection
• Trying multiple Switches with one control signal