Raspberry Pi 2 Model B GPIO 40 Pin Block Pinout

Raspberry Pi 2, Node.js, Ultrasonic Sensor

Note: This Post is based on http://thejackalofjavascript.com/rpi-an-ultrasonic-sensor-measure-distances/ The post here in this link is based on Old Raspberry Pi. which does not work well with Raspberry Pi 2.

Here is the solution:

Components needed

1. 1 – Raspberry pi B+
2. 1 – Breadboard
3. 1 – 1K Ohm resistor
4. 1 – HC-SR04 Ultrasonic sensor
5. 4 – Jumper wires

Understanding HC-SR04 Ultrasonic Sensor

HC-SR04 sensor works with a power of 5v. It has a range of approximately 2cm to 4m. It outputs a frequency of 40khz, twice the human ear can hear. (more info on the sensor here)

As you can see from the above diagram, the HC-SR04 sensor has 4 pins.

1. VCC  : +5v power supply
2. Trigger : A high input to this pin for a duration of 10 micro seconds, activates the sensor
3. Echo : This pin returns the time taken for the transmitted signal to come back after hitting an object.
4. Ground : Connected to the ground

Setup HC-SR04 Ultrasonic Sensor

As you can see from the above diagram, we will connect the VCC pin of the sensor to +5v and GND to GND. We will connect the Trigger pin to GPIO pin 17 and finally we will connect a 1K Ohm resistor between the Echo pin and GPIO pin 18.

The Echo pin outputs a 5V output, which will damage the GPIO pin, if interfaced directly. This is why we connect a 1K Ohm resistor between the Echo and GPIO pin 18.

Node.js Program

Login to your pi via ssh – terminal/putty. As soon as you ssh into pi, you will be landing inside the /home/pi folder. We will create a new folder here named node_programs. And inside this folder, we will be maintaining all our programs. Run

mkdir node_programs

To step inside that folder, run

cd node_programs

For this post, we will create a new folder named ultraSonicSensor and will step inside this folder. Run

mkdir ultraSonicSensor && cd ultraSonicSensor

Note : You can run multiple commands separated by a &&.
First we will initialize a new node project here. Run

npm init

Fill it up as applicable.
Now we will install a node module named 'r-pi-usonic' to interact with the Ultrasonic sensor. Run

npm install r-pi-usonic --save

Now we will install a node module named 'readline'. Run

npm install readline --save

Now we will install a node module named 'math-statistics' to interact with the Ultrasonic sensor. Run

npm install math-statistics --save

Next, we will create a new file named sense.js. And we will open the same in the nano editor. Run

nano sense.js

Paste the below code into the nano editor (Filename: /home/pi/node_programs/ultraSonicSensor/sense.js)

'use strict';

var readline   = require('readline');
var statistics = require('math-statistics');
var usonic     = require('./node_modules/r-pi-usonic/lib/usonic.js');

var print = function (distances) {
    var distance = statistics.median(distances);

    process.stdout.clearLine();
    process.stdout.cursorTo(0);

    if (distance < 0) {
        process.stdout.write('Error: Measurement timeout.\n');
    } else {
        process.stdout.write('Distance: ' + distance.toFixed(2) + ' cm');
    }
};

var initSensor = function (config) {
    var sensor = usonic.createSensor(config.echoPin, config.triggerPin, config.timeout);

    console.log('Config: ' + JSON.stringify(config));

    var distances;

    (function measure() {
        if (!distances || distances.length === config.rate) {
            if (distances) {
                print(distances);
            }

            distances = [];
        }

        setTimeout(function () {
            distances.push(sensor());

            measure();
        }, config.delay);
    }());
};
Run this program now:

sudo node surveyor.js