Introduction: Ultrasonic Distance Sensor

By Tinkercad Circuits
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Let's measure distances with an ultrasonic rangefinder (distance sensor) and Arduino's digital input. We'll connect up a circuit using a breadboard and use some simple Arduino code to control a single LED.

You may have already learned to read a pushbutton and PIR motion sensor with Arduino's digital input, and we'll build on those skills in this lesson.

Ultrasonic rangefinders use sound waves to bounce off objects in front of them, much like bats using echolocation to sense their environment. The proximity sensor sends out a signal and measures how long it takes to return. The Arduino program receives this information and calculates the distance between the sensor and object.

  1. Explore the sample circuit here in the workplane by starting the simulation and clicking on the proximity sensor. This will activate a highlighted area in front of the sensor with a circle "object" inside. You may need to resize the view if the circle is off screen.
  2. Click and drag the "object" circle closer and further away, noticing the changing distance values on screen.
  3. In this lesson, you'll build this simulated circuit yourself along side the sample. To optionally build the physical circuit, gather up your Arduino Uno board, USB cable, solderless breadboard, three LEDs, resistors (any value from 100-1K), ultrasonic rangefinder, and breadboard wires.
  4. Continue to the next step.

Ultrasonic Distance Sensor LED Bar Graph (Blocks)

Step 1: Build the LED Circuit

Just as you’ve learned from the introductory lessons, start by wiring up your Arduino and breadboard with power and ground next to the example circuit, then add the the three red LEDs to the breadboard, as shown. These will be the "bar graph" lights for visually indicating the sensor's distance measurement.

  1. Drag an Arduino Uno and breadboard from the components panel to the workplane, next to the existing circuit.
  2. Connect the 5 volt and ground pins on the Arduino to the power (+) and ground (-) rails on the breadboard with wires. You can change the wire colors if you want to! Either use the inspector dropdown or the number keys on your keyboard.
  3. Drag three LEDs on the breadboard in row E, spaced 2 breadboard sockets apart. You can change the LED color using the inspector that pops up when you click on each one.
  4. Use a 220 Ohm resistor to connect each LED's cathode (left leg) to the ground rail (black) of the breadboard. You can change a resistor's value by highlighting it and using the dropdown menu.
  5. Connect the LED anodes (right legs) to digital pins 4, 3, and 2 on the Arduino. Stuck?
  6. HINT:
  7. The LED anode (+) is the terminal that current flows into. This will connect to the digital output pins on the Arduino. The cathode (-) is the terminal that current flows from. This will connect to the ground rail.
  8. Continue to the next step.

Step 2: Add Proximity Sensor

Proximity sensors come in multiple flavors. Here in Tinkercad Circuits, you can choose between a three-pin sensor or a four-pin sensor. In general, ultrasonic rangefinders have one pin that connects to ground, another that connects to 5 volts, a third for sending a signal, and a fourth for receiving a signal. The 'send' and 'receive' pins are combined into one pin on the three-pin flavor.

  1. In the circuits editor, find the ultrasonic rangefinder in the components drawer. To find the four-pin sensor, view "All" in the components panel (using the dropdown menu).
  2. Place the sensor on the breadboard to the left of the LEDs in row E, as shown in the figure.
  3. Wire up the sensor so the 5V pin connects to the 5V voltage rail, the GND pin connects to the ground rail, the SIG or TRIG pin to Arduino pin 7, and, if using the four-pin flavor, the ECHO pin connects to Arduino pin 6.
  4. Continue to the next step.

Step 3: Code With Blocks

Let's use the code blocks editor to listen to the state of the sensor, then make decisions about which LEDs to light up based on the sensor's value.

  1. Click the "Code" button to open the code editor. The grey Notation blocks are comments for making note of what you intend for your code to do, but this text isn't required or executed as part of the program.
  2. Click on the Variables category in the code editor. Create a new variable called distanceThreshold and use a "set" block to set it to 350 (centimeters).
  3. To store the sensor value, create a variable named "cm".
  4. Drag out a "set" block and adjust the dropdown to our new variable cm.
  5. In the Input category, drag out a "read ultrasonic distance sensor on" block, and place it inside the set block.
  6. Adjust the dropdown menus inside the input block to set the trigger pin to 7, the echo pin to "same as trigger" and units to cm.
  7. Optionally create a new variable for converting centimeters to inches with a set block and an arithmetic block to read "set inches to (cm / 2.54)".
  8. Add some serial monitoring blocks to print out the sensor distance in centimeters and inches.
  9. Click the Control category and drag out an if then block, then navigate to Math and drag a comparator block onto the if block.
  10. In the Variables category, grab the cm variable and the distanceThreshold variable and drag them into the comparator block, adjusting the dropdown so it reads "if cm > distanceThreshold then".
  11. Add three digital output blocks inside the if statement to set pins 2, 3, and 4 LOW.
  12. Duplicate this if statement four times and add arithmetic blocks and and/or blocks to create five total state detection if statements. The first state is "the distance is farther than our threshold" so no LEDs light up. When the distance is closer than or equal to the distanceThreshold and greater than distanceThreshold-100, light up only pin 2's LED. When the temperature is between distanceThreshold-100 and distanceThreshold-250, light up two LEDs. And so on to account for all the desired states.
  13. Continue to the next step.

Step 4: Ultrasonic Rangefinder Arduino Code Explained

When the code editor is open, you can click the dropdown menu on the left and select "Blocks + Text" to reveal the Arduino code generated by the code blocks. Follow along as we explore the code in more detail.

  1. int distanceThreshold = 0;int cm = 0;int inches = 0;

    Before the setup(), we create variables to store the target distance threshold, as well as the sensor value in centimeters (cm) and inches. They're called int because they are integers, or any whole number.

  2. long readUltrasonicDistance(int triggerPin, int echoPin){  pinMode(triggerPin, OUTPUT);  // Clear the trigger  digitalWrite(triggerPin, LOW);  delayMicroseconds(2);  // Sets the trigger pin to HIGH state for 10 microseconds  digitalWrite(triggerPin, HIGH);  delayMicroseconds(10);  digitalWrite(triggerPin, LOW);  pinMode(echoPin, INPUT);  // Reads the echo pin, and returns the sound wave travel time in microseconds  return pulseIn(echoPin, HIGH);}

    The next section is a special bit of code for reading the ultrasonic distance sensor. It's called a function. So far you are familiar with setup() and loop(), but in this sketch, the function readUltrasonicDistance() is used to describe the sensor code and keep it separate from the main body of the program. The function definition starts with what type of data the function will return, or send back to the main program. In this case the function returns a long, which is a decimal point number with many digits. Next is the name of the function, which is up to you. Then in parentheses are the arguments the function takes. int triggerPin, int echoPin are the variable declarations for your sensor's connection pins. The pin numbers will be specified when you call the function in the main program loop(). Inside the function, these local variables are used to reference the information you passed to it from the main loop (or from another function). The function itself sends a signal through the triggerPin and reports back the time it takes to get the signal back over echoPin.

  3. void setup(){  Serial.begin(9600);  pinMode(2, OUTPUT);  pinMode(3, OUTPUT);  pinMode(4, OUTPUT);}

    Inside the setup, pins are configured using the pinMode() function. The serial monitor connection is established with Serial.begin. Pins 2, 3, and 4 are configured as outputs to control the LEDs.

  4. void loop(){  // set threshold distance to activate LEDs  distanceThreshold = 350;  // measure the ping time in cm  cm = 0.01723 * readUltrasonicDistance(7, 6);

    In the main loop, distanceThreshold is set to its target 350cm.

  5. // convert to inches by dividing by 2.54  inches = (cm / 2.54);  Serial.print(cm);  Serial.print("cm, ");  Serial.print(inches);  Serial.println("in");

    To convert centimeters to inches, divide by 2.54. Printing to the serial monitor helps you observe the distance change more granularly than the LED states show alone.

  6. if (cm > distanceThreshold) {    digitalWrite(2, LOW);    digitalWrite(3, LOW);    digitalWrite(4, LOW);  }  if (cm <= distanceThreshold && cm > distanceThreshold - 100) {    digitalWrite(2, HIGH);    digitalWrite(3, LOW);    digitalWrite(4, LOW);  }  if (cm <= distanceThreshold - 100 && cm > distanceThreshold - 250) {    digitalWrite(2, HIGH);    digitalWrite(3, HIGH);    digitalWrite(4, LOW);  }  if (cm <= distanceThreshold - 250 && cm > distanceThreshold - 350) {    digitalWrite(2, HIGH);    digitalWrite(3, HIGH);    digitalWrite(4, HIGH);  }  if (cm <= distanceThreshold - 350) {    digitalWrite(2, HIGH);    digitalWrite(3, HIGH);    digitalWrite(4, HIGH);  }  delay(100); // Wait for 100 millisecond(s)}

    The loop's six if statements evaluate for different ranges of distance between 0 and 350cm, lighting up more LEDs the closer the object.

  7. If you want to see a more obvious change in bar graph lights, you can change the distanceThreshold variable and/or the range that you are looking at by changing the arguments in the if() statements. This is called calibration.
  8. Continue to the next step.

Step 5: Build a Physical Circuit (Optional)

If you build a physical version of this circuit, you can try it out with the Arduino software's serial monitor (magnifying glass button in the upper right of the sketch window), activating the sensor with your hand, body, notebook, etc.

  1. If using a physical board, put something in front of the sensor and observe the distance reading using the serial monitor, and set distanceThreshold to that value.
  2. Adjust your different distance threshold "buckets" to a range suitable to your initial value, for instance if your hand was 60cm away, your ranges might be 60-40, 40-20, and 20-0.
  3. Upload your code again, and try moving in front of the sensor. As the distance shortens, you should see the LEDs turn on one by one.
  4. Continue to the next step.

Step 6: Next, Try...

Congratulations! You have learned to detect distance using an ultrasonic sensor. You also learned about standalone functions in this lesson, and used and the serial monitor to track changes inside your Arduino. Here are a few ways to expand this project:

  1. Make a proximity alarm by adding a piezo buzzer that turns on when all three LEDs are lit up (closest distance).
  2. Add motors to create a robot with obstacle detection!