Comp 1811 Computer Systems for the Professional

Ultrasonic Range Sensor

Color Coding for this Worksheet
Information
Instructed Learning
Autonomous Learning

Activities

1 / The Ultrasonic Range Sensor works rather like ultrasonic radar in submarines. The Arduino sends a pulse to the sensor which then sends out a burst of ultrasonic sound. It then waits for the echo to come back from an obstacle, and the sensor provides an output pulse when it arrives. Since the Arduino sends the first pulse and receives the second, it can use the time difference between these two pulses to calculate the distance of the obstacle.
Here’s the pulses and acoustic bursts:

(a) First carefully connect the sensor to the Arduino like this

(b) Download the Arduino Sketches for today from the zipped file ArduinoSketches and open up the template sketch HC_SR04 and in the loop() functions, add the following lines of code. Keep an eye on the diagram of pulses and acoustic bursts above, since your code will create these!
(i) Send the TxPin (digi10) low, and keep it low for 5 microseconds. This corresponds to the short low part of the “Trigger” signal; use delayMicroseconds(…); to do this.
(ii) Now make the TxPin high for 10 microseconds and then send it low. This corresponds to the remaining part of the “Trigger” signal.
(iii) Now write the following line of code which is an Arduino function to wait for a pulse to arrive on the RxPin (digi11).
travelTime = pulseIn(RxPin,HIGH);
(iv) Now write the following line of code to convert the travel time into a distance in cms. How does this work? Well since speed = distance/time, distance = speed x time. The speed of sound is 330 m/s and the factor 20000.0 is to scale the travelTime (in microseconds) and the distance to cms.
dist = (float)travelTime*330.0/20000.0;
(v) Add a line of code to send dist to the serial monitor and after that a line of code to delay for 500ms.
(vi) Fire up the serial monitor and hold your hand in front of the sensor and check that you get a sensible reading.
2 / Now let’s perform some investigations with the sensor. It’s probably best to point the sensor upwards to the ceiling to avoid spurious reflections.
(a) First consult the sensor datasheet. Find out two important parameters (i) the ranging distance, both min and max, (ii) the half-beamwidth angle, i.e., half the total beamwidth.
(b) Check the range accuracy of the sensor. Hold an obstacle above the sensor, e.g. 20cms, 100cms and check the distance reading. What is the closest and the furthest the sensor is useful?
(c) Measure the height of the lab above the floor.
(c) Measure the angle from the vertical at which the sensor just detects an obstacle. Look at the diagram below. Move the obstacle in from the side making sure that the obstacle remains 100cm above the sensor. Note the distance x in cm where the object is detected. Then calculate the angle θ by entering the following formula into Excel =180*ATAN(20/100)/PI() Note here my value of x was 20.The mathematical formula is
180πatanx100