Signal routing (Mux, Demux, Switch) in Simulink - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Mux block that combines two signals.

Simulink

muxBlock = add_block('simulink/Signal Routing/Mux', 'model/Mux');
set_param(muxBlock, 'Inputs', '[1]');

Drag options to blanks, or click blank then click option'

A4

B1

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Setting 'Inputs' to 1 will not combine multiple signals.

Using a number larger than the actual inputs can cause errors.

The Mux block combines multiple input signals into a single output signal. Setting 'Inputs' to '2' means it will combine two signals.

2fill in blank

medium

Complete the code to create a Demux block that splits a signal into three outputs.

Simulink

demuxBlock = add_block('simulink/Signal Routing/Demux', 'model/Demux');
set_param(demuxBlock, 'Outputs', '[1]');

Drag options to blanks, or click blank then click option'

A3

B2

C4

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting 'Outputs' to 1 will not split the signal.

Using a number larger than the input signal width causes errors.

The Demux block splits a single input signal into multiple output signals. Setting 'Outputs' to '3' means it will split into three signals.

3fill in blank

hard

Fix the error in the code to set the Switch block criteria to select input 2 when control signal is greater than 5.

Simulink

switchBlock = add_block('simulink/Signal Routing/Switch', 'model/Switch');
set_param(switchBlock, 'Criteria', '[1]');

Drag options to blanks, or click blank then click option'

Au2 < 5

Bu2 > 5

Cu2 == 5

Du2 >= 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'u2 >= 5' selects input 2 when control signal is equal to 5, which is not required.

Using 'u2 < 5' or 'u2 == 5' does not match the condition.

The Switch block uses the 'Criteria' parameter to decide which input to pass. 'u2 > 5' means it selects input 2 when the control signal is greater than 5.

4fill in blank

hard

Fill both blanks to create a Mux block with four inputs and a Demux block with four outputs.

Simulink

muxBlock = add_block('simulink/Signal Routing/Mux', 'model/Mux');
set_param(muxBlock, 'Inputs', '[1]');
demuxBlock = add_block('simulink/Signal Routing/Demux', 'model/Demux');
set_param(demuxBlock, 'Outputs', '[2]');

Drag options to blanks, or click blank then click option'

A4

B3

C2

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between Mux inputs and Demux outputs causes errors.

Using numbers other than 4 will not handle four signals correctly.

Both the Mux and Demux blocks are set to handle four signals by setting 'Inputs' and 'Outputs' to '4'.

5fill in blank

hard

Fill all three blanks to create a Switch block that selects input 2 when control signal is greater than 10, and set the threshold accordingly.

Simulink

switchBlock = add_block('simulink/Signal Routing/Switch', 'model/Switch');
set_param(switchBlock, 'Criteria', '[1]');
set_param(switchBlock, 'Threshold', '[2]');
set_param(switchBlock, 'InputPort', '[3]');

Drag options to blanks, or click blank then click option'

Au2 >= 10

B10

C2

Du2 > 10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'u2 >= 10' includes equal to 10, which is not required.

Setting threshold or input port incorrectly causes wrong signal selection.

The Switch block criteria is set to 'u2 > 10' to select input 2 when control signal is greater than 10. The threshold is set to 10, and the input port to select is 2.

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