Signal routing (Mux, Demux, Switch) in Simulink - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the role of a Mux block in Simulink

What is the primary function of a Mux block in Simulink when routing signals?

A It combines multiple input signals into a single output signal vector.

B It splits a single input signal vector into multiple output signals.

C It switches between multiple input signals based on a control signal.

D It amplifies the input signal before routing it to outputs.

💡 Hint

Think about how multiple signals can be grouped together in one line.

A Mux block takes several input signals and combines them into one vector signal. This is useful for grouping signals for processing or routing.

🧠 Conceptual

intermediate

Function of a Demux block in signal routing

What does a Demux block do in a Simulink model?

A It splits a vector signal into multiple scalar signals.

B It merges multiple signals into one vector signal.

C It selects one input signal to pass through based on a control input.

D It delays the input signal by a fixed time.

💡 Hint

Consider the opposite of combining signals.

A Demux block takes a vector input and splits it into separate scalar outputs, allowing individual signals to be processed separately.

❓ Predict Output

advanced

Output of a Switch block with given inputs

Given a Switch block in Simulink with inputs: Data input 1 = 5, Data input 2 = 10, and Control input = 0, what is the output of the Switch block?

Simulink

Data input 1 = 5
Data input 2 = 10
Control input = 0
Switch block outputs Data input 1 if Control input >= Threshold (default 0), else Data input 2.

A Error due to invalid control input

B 5

C 10

D 0

💡 Hint

Check the default threshold and compare the control input value.

The Switch block outputs Data input 1 when the control input is greater than or equal to the threshold (default 0). Since control input is 0, output is 5.

❓ data_output

advanced

Number of output signals from a Demux block

If a Demux block receives a vector input signal of size 6, how many output signals will it produce?

A Depends on the control input

B 1

C 3

D 6

💡 Hint

Each element of the input vector becomes one output.

A Demux block outputs one signal for each element in the input vector. So, a vector of size 6 produces 6 outputs.

🚀 Application

expert

Choosing the correct block for dynamic signal selection

You want to build a Simulink model that dynamically selects one of three input signals based on a control signal that can be 1, 2, or 3. Which block should you use to achieve this behavior?

A Mux block

B Switch block

C Multiport Switch block

D Demux block

💡 Hint

Consider a block that can select among multiple inputs based on an index.

The Multiport Switch block allows selection among multiple inputs based on a control index signal, perfect for choosing one of three signals dynamically.

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