• Ultrasonic Sensor

    Developed by Dr James E. Pickering

    This exercise shows how to configure an HC-SR04 ultrasonic sensor with an Arduino Uno, acquire distance measurements in Simulink, and apply Last Good Value logic to handle invalid or intermittent sensor readings.

    SensorHC-SR04 ultrasonic distance measurement
    Range0.02 m to 4.00 m operating range
    LogicLast Good Value filtering for invalid readings

    Contents

    1. Learning Outcomes 2. Requirements 3. Hardware Set-Up 4. Simulink Set-Up and Distance Measurement Testing 5. Last Good Value Logic Filter and Testing 6. Additional Exercises 7. Concluding Remarks

    1. Learning Outcomes

    After completing this exercise, learners should be able to acquire distance measurements using a digital ultrasonic sensor and implement simple logic to manage unreliable readings.

    Acquire distance measurements using a digital ultrasonic sensor

    Explain and demonstrate how an HC-SR04 ultrasonic sensor can be configured with Arduino and Simulink to measure object distance.

    Design and implement Last Good Value logic

    Build a Last Good Value logic filter to manage erroneous or intermittent readings from a digital sensor.

    2. Requirements

    Configure the HC-SR04 ultrasonic sensor and Arduino Uno to measure object distance within the specified operating range of 0.02 m to 4.00 m.

    Select, configure, and justify an appropriate sampling interval, such as 0.01 seconds, to support responsive measurement performance.

    Compare measured distances against at least three known reference distances and comment on accuracy and repeatability.

    Implement a Last Good Value filter using suitable Simulink logic blocks.

    Experimentally demonstrate that invalid readings hold the last valid measurement and that normal operation resumes once valid data returns.

    3. Hardware Set-Up

    This exercise involves connecting an HC-SR04 ultrasonic sensor to an Arduino Uno to measure distance. The ACE-Box Base + Sense can be used, but it is not required; the individual components are sufficient.

    Required hardware

    • Arduino Uno board supported by Simulink
    • USB cable Type A to B
    • Breadboard
    • Ultrasonic HC-SR04 sensor
    • 4 male-to-male wires

    HC-SR04 ultrasonic specifications

    • Distance measurement range: 0.02 to 4.00 metres
    • Accuracy: +/-0.003 metres

    Connect the ultrasonic sensor directly to the breadboard.

    Connect the Trig signal to Arduino pin 5 and the Echo signal to Arduino pin 4.

    Connect the VCC terminal of the sensor to the 5 V supply pin on the Arduino Uno.

    Connect the GND terminal of the sensor to a GND pin on the Arduino Uno.

    Arduino Uno connected to an HC-SR04 ultrasonic sensor
    Hardware wiring for the HC-SR04 ultrasonic sensor and Arduino Uno.

    5. Last Good Value Logic Filter and Testing

    A Last Good Value filter maintains a valid output when the sensor signal becomes unreliable or invalid. It remembers the last valid input value and continues to output this value until a new valid reading is received.

    Switch block

    The Switch block controls the flow of data based on the sensor output and the selected validity threshold.

    Memory block

    The Memory block stores the last valid reading so it can be reused when the current sensor output is invalid.

    Build the LGV signal flow

    Arrange the Ultrasonic Sensor, Switch, Memory, Mux, Display, and Scope blocks as shown in the Simulink diagram.

    Configure the Switch block

    Double-click the Switch block and set the threshold logic to pass values greater than 0.1.

    Add signal viewing blocks

    Add a Mux and Scope blocks so that the raw and filtered signals can be viewed in real time.

    Deploy and test

    Deploy the model and test the operation by moving the sensor within 0.1 metres and then beyond this threshold.

    Last Good Value logic filter Simulink diagram and scope output
    Last Good Value logic filter and example scope response.

    6. Additional Exercises

    Exercise 1: Sampling Time Investigation

    Test at least three different sampling intervals and comment on the performance of the measurements.

    Exercise 2: Static Accuracy Check

    Measure three known distances and compare the sensor readings against the reference values.

    Exercise 3: Improved Validity Logic

    Replace the 0.1 threshold with a full range check from 0.02 m to 4.00 m and compare the behaviour.

    Exercise 4: Moving Target Test

    Move an object towards and away from the sensor and observe signal smoothness and delay.

    7. Concluding Remarks

    The exercises have demonstrated practical distance measurement using an ultrasonic sensor integrated with Simulink and Arduino hardware. The exercise reinforces correct hardware configuration, real-time data acquisition, and validation of sensor signals.

    The implementation of the Last Good Value filter highlights the importance of basic signal conditioning to improve measurement reliability. These principles form the foundation for closed-loop control systems and autonomous sensing applications such as parking aids.

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