MME2151: A Contactless Distance Measuring Sensor is a Useful Tool in Various Applications: Electro-Mechanical Systems Technology Assignment, SIT, Singapore

Background

A contactless distance measuring sensor is a useful tool in various applications including positioning, locating, dimensioning, selecting, leveling, controlling, and profiling. By performing additional mathematical calculations with the distance measurements, we can also estimate the speed and various other physical dimensions. Contactless measurement has widespread applications in the field of robotics.

An ultrasonic sound wave can be used for distance measurement without making any physical contact. This is especially useful in robotics where the distance to obstacles is needed in collision avoidance algorithms. The Ultrasonic sound technique mimics the behavior of bats where the ECHO from the obstacle is used to measure distance. In this project, we will design an ultrasonic distance measuring sensor using the HC-SR04 ultrasonic module with Arduino and a 16×2 LCD display.

Theory

The principle of detecting distance from echo is illustrated in Figure 1. The basic idea is to use a radiation source to transmit a radiation wave, this wave travels through the medium and gets reflected when it hits a target of interest. The reflected echo is then detected by a receiver tuned to the frequency of the transmitted wave. In practice, the different radiation sources can be used, these include (a) radio frequency wave (radar), (b) Electromagnetic wave (laser), and sonic wave (ultrasound). The time interval between transmission and reception of the radiation is also known as the time of flight (TOF). The distance measured is computed as follows using the TOF as follows:

Distance = (Time of Flight x Velocity of Radiation)/2

Assuming that the radiation source and the receiver are collocated, then, the distance travelled by the radiation wave is twice the distance from the source/receiver to the object; this is because the signal has to travel from source to target of interest and then back from the target of interest to the receiver.

Project Deliverables

Your project report must address the following requirements:

1. Answers to the following questions:

• If the source of radiation is a laser, what is the distance measured if the TOF is 2µs?
• What is the TOF if the distance measure is 2ms using an ultrasonic sensor?
• Work out the scale needed to convert the distance measured from m to cm.
• Name two possible applications for a contactless distance measuring sensor. You may use any of the three types of radiation sources, i.e. radar, laser, ultrasound.

2. Implement your circuit and design an experiment to validate the performance of the contactless distance measurement sensor. Explain clearly how you verify the accuracy of your measurements and show experiment data to substantiate your results. Determine the mean error and the 1σ error of your sensor. Explain what you think is the main cause of error in your design.

3. Discuss how you can modify your design to measure the relative velocity of a moving object in front of the sensor. Describe the principle behind your method. Modify the code to provide relative velocity measurements. Design an experiment to display both the distance and relative velocity on your LCD.

You may use pictures to describe your experimental setup and tables to illustrate data collected from experiments. Use charts and plots to explain how you derive the mean accuracy, the 1σ error as well as other performance parameters of your sensor.