RETIRED - SparkFun Inventor's Kit Experiment Guide - v4.0

Contributors: Joel_E_B

Circuit 3B: Distance Sensor

Distance sensors are amazing tools with all kinds of uses. They can sense the presence of an object, they can be used in experiments to calculate speed and acceleration, and they can be used in robotics to avoid obstacles. This circuit will walk you through the basics of using an ultrasonic distance sensor, which measures distance using sound waves!

Parts Needed

Grab the following quantities of each part listed to build this circuit:

New Components

Ultrasonic Distance Sensor

Distance sensors work by sending pulses of light or sound out from a transmitter, then timing how long it takes for the signals to bounce off an object and return to a receiver (just like sonar). Some sensors use infrared light, some use lasers, and some, like the HC-SR04 included in your kit, use ultrasonic sound (sound so high-pitched that you can’t hear it).

New Concepts

Datasheets

When working with electronics, datasheets are your best friend. Datasheets contain all the relevant information needed to get you up and running with a part. In this circuit, we are calculating distance based on the time it takes sound waves to be transmitted, bounce off an object and then be received. But, how can we tell distance from that information? The answer lies in the datasheet for the distance sensor. In it, you can find the equation the program needs to interpret distance from the time it takes the sound wave to travel.

Else If Statement

In the night-light circuit, you used an if/else statement to run one set of code when a logic statement was true, and a different set of code when it was false. What if you wanted to have more than two options? Else if statements let you run as many logical tests as you want in one if statement. For example, in the code for this circuit, there is an if statement that flows like this:

1. If the distance is less than 10, make the RGB LED red.
2. Else if the distance is more than 10 but less than 20, make the RGB LED yellow.
3. Else make the RGB LED green.

If you wanted to have four or five colors for different distances, you could add more else if statements.

Else if statements are different from nested if statements in that only one of the statements above can be true, whereas you could have multiple nested if statements that could true.

Hardware Hookup

The distance sensor is polarized. Take note of the pin labels when connecting your circuit.

The following table describes the function of each pin on the distance sensor:

Ready to start hooking everything up? Check out the Fritzing diagram below to see how everything is connected.

Circuit Diagram

Hookup Table

Open the Sketch

To open the code, go to: File > Examples > SIK_Guide_Code-V_4 > SIK_Circuit_3B-DistanceSensor

You can also copy and paste the following code into the Arduino IDE. Hit upload, and see what happens!

language:cpp
/*
SparkFun Inventor’s Kit
Circuit 3B-Distance Sensor

Control the color of an RGB LED using an ultrasonic distance sensor.

This sketch was written by SparkFun Electronics, with lots of help from the Arduino community.
This code is completely free for any use.

View circuit diagram and instructions at: https://learn.sparkfun.com/tutorials/sparkfun-inventors-kit-experiment-guide---v40
Download drawings and code at: https://github.com/sparkfun/SIK-Guide-Code
*/

const int trigPin = 11;           //connects to the echo pin on the distance sensor       
const int echoPin = 12;           //connects to the trigger pin on the distance sensor      

const int redPin = 3;             //pin to control the red LED inside the RGB LED
const int greenPin = 5;           //pin to control the green LED inside the RGB LED
const int bluePin = 6;            //pin to control the blue LED inside the RGB LED

float distance = 0;               //stores the distance measured by the distance sensor

void setup()
{
  Serial.begin (9600);        //set up a serial connection with the computer

  pinMode(trigPin, OUTPUT);   //the trigger pin will output pulses of electricity 
  pinMode(echoPin, INPUT);    //the echo pin will measure the duration of pulses coming back from the distance sensor

  //set the RGB LED pins to output
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
}

void loop() {
  distance = getDistance();   //variable to store the distance measured by the sensor

  Serial.print(distance);     //print the distance that was measured
  Serial.println(" in");      //print units after the distance

  if(distance <= 10){                         //if the object is close

    //make the RGB LED red
    analogWrite(redPin, 255);
    analogWrite(greenPin, 0);
    analogWrite(bluePin, 0);

  } else if(10 < distance && distance < 20){  //if the object is a medium distance

    //make the RGB LED yellow
    analogWrite(redPin, 255);
    analogWrite(greenPin, 50);
    analogWrite(bluePin, 0);

  } else{                                     //if the object is far away

    //make the RGB LED green
    analogWrite(redPin, 0);
    analogWrite(greenPin, 255);
    analogWrite(bluePin, 0);    
  }

  delay(50);      //delay 50ms between each reading
}

//------------------FUNCTIONS-------------------------------

//RETURNS THE DISTANCE MEASURED BY THE HC-SR04 DISTANCE SENSOR
float getDistance()
{
  float echoTime;                   //variable to store the time it takes for a ping to bounce off an object
  float calcualtedDistance;         //variable to store the distance calculated from the echo time

  //send out an ultrasonic pulse that's 10ms long
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10); 
  digitalWrite(trigPin, LOW);

  echoTime = pulseIn(echoPin, HIGH);      //use the pulsein command to see how long it takes for the
                                          //pulse to bounce back to the sensor

  calcualtedDistance = echoTime / 148.0;  //calculate the distance of the object that reflected the pulse (half the bounce time multiplied by the speed of sound)

  return calcualtedDistance;              //send back the distance that was calculated
}

What You Should See

Move your hand or a large, flat object closer and farther away from the distance sensor. As the object approaches, the light will change from green to yellow to red.

Open the Serial Monitor, and you should see the distance printed to the window.

Program Overview

1. Check what distance the sensor is reading. a. If the distance is less than 10 inches, make the RGB LED red. b. If the distance is between 10 and 20 inches, make the RGB LED yellow. c. If the distance value is not equal to the fist two conditions, make the RGB LED green.

Code to Note

Coding Challenges

Troubleshooting