Signal routing (Mux, Demux, Switch) in Simulink - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Mux block in Simulink?

A Mux (Multiplexer) block combines multiple input signals into a single output signal, allowing you to route several signals together.

beginner

What does a Demux block do in Simulink?

A Demux (Demultiplexer) block splits a single input signal into multiple output signals, separating combined signals back into individual parts.

beginner

How does a Switch block work in Simulink?

A Switch block routes one of its input signals to the output based on a control signal or condition, like choosing which path to follow.

intermediate

Why use a Mux block instead of connecting signals directly?

Using a Mux block keeps your model organized by grouping signals together, making it easier to manage and visualize multiple signals as one.

intermediate

What is a practical example of using a Switch block?

A Switch block can select between two sensor readings based on a condition, like choosing the temperature sensor reading only if it is valid.

What does a Demux block do in Simulink?

A Combines multiple signals into one

B Selects one signal based on a condition

C Splits one signal into multiple signals

D Filters signals based on frequency

A Demux block splits a single input signal into multiple output signals.

Which block would you use to combine three signals into one?

A Mux

B Demux

C Switch

D Gain

A Mux block combines multiple input signals into a single output.

How does a Switch block decide which input to send to output?

A Based on signal amplitude

B Based on signal frequency

C Randomly

D Based on a control signal or condition

A Switch block routes signals based on a control input or condition.

What is the main benefit of using Mux and Demux blocks?

A To increase signal strength

B To organize and manage multiple signals

C To filter noise from signals

D To convert analog signals to digital

Mux and Demux blocks help organize and manage multiple signals in a model.

If you want to select between two sensor inputs based on a condition, which block should you use?

A Switch

B Demux

C Mux

D Sum

A Switch block selects one input based on a condition or control signal.

Explain how Mux, Demux, and Switch blocks help in signal routing within a Simulink model.

Think about how signals flow and are managed in a model.

Describe a real-life example where you might use a Switch block in a Simulink model.

Imagine deciding which data to use depending on a situation.

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