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Concept visual
Start at both ends
In the previous chapters we have learned how to use WebSocket, and how to use GPIO to turn LEDs on and off. In this we will use chapter we use a RGB LED, with PWM (Pulse-width modulation) to display different colors based on user input via WebSocket. An RGB LED is a LED with 3 different colors. It has a RED, GREEN and BLUE LED (RGB LED). And using PWM, we can set the individual strength of the 3 LEDs. This will allow us to mix them, to set a color.
In this chapter we will create an example where we control an RGB LED with a web page via WebSocket.
A Raspberry Pi with Raspian, internet, SSH, with Node.js installed The pigpio module for Node.js The socket.io module for Node.js 1 x
3 x 220
1 x
(common anode or common cathode) 4 x
Click the links in the list above for descriptions of the different components.
The resistor you need can be different from what we use depending on the type of LED you use. Most small LEDs only need a small resistor, around 200-500 ohms. It is generally not critical what exact value you use, but the smaller the value of the resistor, the brighter the LED will shine.
Earlier, we have used the "onoff" module, which works great for just turning on and off. Now we want to set the set the strength of the LEDs, so we need a GPIO Module with a bit more functionality. We will use the "pigpio" Node.js module, as this allows for PWM. With PWM we can set the strength of a LED from 0 to 255. The "pigpio" Node.js module is based on the pigpio C library. If you are using the "Lite" version of Raspbian, this is most likely not included and must be manually installed.
Formula
pi@w3demopi:~ $ sudo apt - get updateFormula
pi@w3demopi:~ $ sudo apt - get install pigpioNow we can install the "pigpio" Node.js module using npm: pi@w3demopi:~ $ npm install pigpio Now the "pigpio" module should be installed and we can use it to interact with the GPIO of the Raspberry Pi.
Since the "pigpio" module uses the pigpio C library, it requires root/sudo privileges to access hardware peripherals (like the GPIO).
Now it is time to build the circuit on our Breadboard. If you are new to electronics, we recommend you turn off the power for the Raspberry Pi. And use an anti-static mat or a grounding strap to avoid damaging it. Shut down the Raspberry Pi properly with the command:
Formula
pi@w3demopi:~ $ sudo shutdown - h nowAfter the LEDs stop blinking on the Raspberry Pi, then pull out the power plug from the Raspberry Pi (or turn of the power strip it is connected to). Just pulling the plug without shutting down properly may cause corruption of the memory card. In building this Circuit it is important to know if you have a common anode, or common cathode, RGB LED: You can check with your provider, or test it yourself: Connect cables to GND and 3.3V pin. Connect GND to the longest leg of the RGB LED and the 3.3 V to any other leg. If the it lights up, your RGB LED has a common cathode. If not, it has a common anode.
Formula
Building the Circuit - Common CathodeLook at the above illustration of the circuit. On the Breadboard, connect the RGB LED to the right ground bus column, and make sure that each leg connects to a different row. The longest leg is the common cathode leg. In this example we have connected the LED to rows
Formula
1 - 4, with the common cathode leg connected to row 2 column I. The REDleg is connected to row 1 column J, the GREEN leg is connected to row 3 column J, and the BLUE leg is connected to row 4 column J On the Raspberry Pi, connect the female leg of the first jumper wire to Ground. You can use any
pin. In this example we used Physical Pin 9 ( GND, row 5, left column) On the Breadboard, connect the male leg of the first jumper wire to the same row of the right ground bus column that you connected the common cathode to. In this example we connected it to row 2 column F On the Raspberry Pi, connect the female leg of the second jumper cable to a GPIO pin. We will use this for the RED leg, In this example we used Physical Pin 7 ( GPIO 4, row 4, left column) On the Breadboard, connect the male leg of the second jumper wire to the left ground bus, same row as the RED leg of the LED is connected. In this example we connected it to row 1, column A On the Breadboard, connect a resistor between the left and right ground bus columns for the row with the RED leg of the LED. In this example we have attached it to row 1, column E and F On the Raspberry Pi, connect the female leg of the third jumper cable to a GPIO pin. We will use this for the GREEN leg, In this example we used Physical Pin 11 ( GPIO 17, row 6, left column) On the Breadboard, connect the male leg of the third jumper wire to the left ground bus, same row as the GREEN leg of the LED is connected. In this example we connected it to row 3, column A On the Breadboard, connect a resistor between the left and right ground bus columns for the row with the GREEN leg of the LED. In this example we have attached it to row 3, column E and F On the Raspberry Pi, connect the female leg of the forth jumper cable to a GPIO pin. We will use this for the BLUE leg, In this example we used Physical Pin 13 ( GPIO 27, row 7, left column) On the Breadboard, connect the male leg of the forth jumper wire to the left ground bus, same row as the BLUE leg of the LED is connected. In this example we connected it to row 4, column A On the Breadboard, connect a resistor between the left and right ground bus columns for the row with the BLUE leg of the LED. In this example we have attached it to row 4, column E and F Your circuit should now be complete, and your connections should look pretty similar to the illustration above. Now it is time to boot up the Raspberry Pi, and write the Node.js script to interact with it.
Formula
Building the Circuit - Common AnodeLook at the above illustration of the circuit. On the Breadboard, connect the RGB LED to the right ground bus column, and make sure that each leg connects to a different row. The longest leg is the common anode leg. In this example we have connected the LED to rows
Formula
1 - 4, with the common cathode leg connected to row 2 column I. The REDleg is connected to row 1 column J, the GREEN leg is connected to row 3 column J, and the BLUE leg is connected to row 4 column J On the Raspberry Pi, connect the female leg of the first jumper cable to a GPIO pin. We will use this for the RED leg, In this example we used Physical Pin 7 ( GPIO 4, row 4, left column) On the Breadboard, connect the male leg of the first jumper wire to the left ground bus, same row as the RED leg of the LED is connected. In this example we connected it to row 1, column A On the Breadboard, connect a resistor between the left and right ground bus columns for the row with the RED leg of the LED. In this example we have attached it to row 1, column E and F On the Raspberry Pi, connect the female leg of the second jumper cable to a GPIO pin. We will use this for the GREEN leg, In this example we used Physical Pin 11 ( GPIO 17, row 6, left column) On the Breadboard, connect the male leg of the second jumper wire to the left ground bus, same row as the GREEN leg of the LED is connected. In this example we connected it to row 3, column A On the Breadboard, connect a resistor between the left and right ground bus columns for the row with the GREEN leg of the LED. In this example we have attached it to row 3, column E and F On the Raspberry Pi, connect the female leg of the third jumper cable to a GPIO pin. We will use this for the BLUE leg, In this example we used Physical Pin 13 ( GPIO 27, row 7, left column) On the Breadboard, connect the male leg of the third jumper wire to the left ground bus, same row as the BLUE leg of the LED is connected. In this example we connected it to row 4, column A On the Breadboard, connect a resistor between the left and right ground bus columns for the row with the BLUE leg of the LED. In this example we have attached it to row 4, column E and F On the Raspberry Pi, connect the female leg of the forth jumper wire to 3.3V. In this example we used Physical Pin 1 ( 3.3V, row 1, left column) On the Breadboard, connect the male leg of the forth jumper wire to the same row of the right ground bus column that you connected the common anode to. In this example we connected it to row 2 column F Your circuit should now be complete, and your connections should look pretty similar to the illustration above. Now it is time to boot up the Raspberry Pi, and write the Node.js script to interact with it. Raspberry Pi and Node.js RGB LED and WebSocket Script Go to the "nodetest" directory, and create a new file called " rgbws.js ": pi@w3demopi:~ $ nano rgbws.js The file is now open and can be edited with the built in Nano Editor.
Write, or paste the following:
rgbws.js let http = require('http').createServer(handler); //require http server, and create server with function handler()
let fs = require('fs'); //require filesystem module let io = require('socket.io')(http) //require socket.io module and pass the http object (server)
let Gpio = require('pigpio').Gpio,//include pigpio to interact with the GPIO
ledRed = new Gpio(4, {mode:
Gpio.OUTPUT}), //use GPIO pin 4 as output for REDFormula
ledGreen = new Gpio(17,{mode: Gpio.OUTPUT}), //use GPIO pin 17 as output for GREENFormula
ledBlue = newGpio(27, {mode: Gpio.OUTPUT}), //use GPIO pin 27 as output for BLUE redRGB = 0, //set starting value of RED variable to off (0 for common cathode)
Formula
greenRGB = 0, //set starting value of GREEN variable to off (0 for common cathode)blueRGB = 0; //set starting value of BLUE variable to off (0 for common cathode)//RESET RGB LED
ledRed.digitalWrite(0); // Turn RED
LED off ledGreen.digitalWrite(0); // Turn GREEN LED off ledBlue.digitalWrite(0); // Turn BLUE LED off http.listen(8080);
//listen to port 8080 function handler (req, res) { //what to do on requests to port 8080 fs.readFile(__dirname + '/public/rgb.html', function(err, data) { //read file rgb.html in public folder if (err) {
res.writeHead(404,
{'Content-Type': 'text/html'}); //display 404 on error return res.end("404 Not Found");
}
res.writeHead(200, {'Content-Type': 'text/html'}); //write HTML
res.write(data); //write data from rgb.html return res.end();
});
}
io.sockets.on('connection', function
(socket) {// Web Socket Connection socket.on('rgbLed', function(data) { //get light switch status from client console.log(data); //output data from WebSocket connection to console
//for common cathode RGB LED 0 is fully off, and 255 is fully on redRGB=parseInt(data.red);
greenRGB=parseInt(data.green);
blueRGB=parseInt(data.blue);
ledRed.pwmWrite(redRGB); //set RED LED to specified value ledGreen.pwmWrite(greenRGB); //set GREEN LED to specified value ledBlue.pwmWrite(blueRGB); //set BLUE});
});
process.on('SIGINT', function () { //on ctrl+c ledRed.digitalWrite(0); // Turn RED LED
off ledGreen.digitalWrite(0); // Turn GREEN LED off ledBlue.digitalWrite(0); // Turn BLUE LED off process.exit(); //exit completely
});
Press "" to save the code. Confirm with " y ", and confirm the name with "
".
Write, or paste the following:
rgbws.js let http = require('http').createServer(handler); //require http server, and create server with function handler()
let fs = require('fs'); //require filesystem module let io = require('socket.io')(http) //require socket.io module and pass the http object (server)
let Gpio = require('pigpio').Gpio,//include pigpio to interact with the GPIO
ledRed = new Gpio(4, {mode:
Gpio.OUTPUT}), //use GPIO pin 4 as output for REDFormula
ledGreen = new Gpio(17,{mode: Gpio.OUTPUT}), //use GPIO pin 17 as output for GREENFormula
ledBlue = newGpio(27, {mode: Gpio.OUTPUT}), //use GPIO pin 27 as output for BLUE redRGB = 255, //set starting value of RED variable to off (255 for common anode)
Formula
greenRGB = 255, //set starting value of GREEN variable to off (255 for common anode)blueRGB = 255; //set starting value of BLUE variable to off (255 for common anode)//RESET RGB LED
ledRed.digitalWrite(1); // Turn RED
LED off ledGreen.digitalWrite(1); // Turn GREEN LED off ledBlue.digitalWrite(1); // Turn BLUE LED off http.listen(8080);
//listen to port 8080 function handler (req, res) { //what to do on requests to port 8080 fs.readFile(__dirname + '/public/rgb.html', function(err, data) { //read file rgb.html in public folder if (err) {
res.writeHead(404,
{'Content-Type': 'text/html'}); //display 404 on error return res.end("404 Not Found");
}
res.writeHead(200, {'Content-Type': 'text/html'}); //write HTML
res.write(data); //write data from rgb.html return res.end();
});
}
io.sockets.on('connection', function
(socket) {// Web Socket Connection socket.on('rgbLed', function(data) { //get light switch status from client console.log(data); //output data from WebSocket connection to console
//for common anode RGB LED 255 is fully off, and 0 is fully on, so we have to change the value from the client redRGB=255-parseInt(data.red);
greenRGB=255-parseInt(data.green);
blueRGB=255-parseInt(data.blue);
console.log("rbg: "
+ redRGB + ", " + greenRGB + ", " + blueRGB); //output converted to console ledRed.pwmWrite(redRGB); //set RED LED to specified value ledGreen.pwmWrite(greenRGB); //set GREEN LED to specified value ledBlue.pwmWrite(blueRGB); //set BLUE});
});
process.on('SIGINT', function () { //on ctrl+c ledRed.digitalWrite(1); // Turn RED LED
off ledGreen.digitalWrite(1); // Turn GREEN LED off ledBlue.digitalWrite(1); // Turn BLUE LED off process.exit(); //exit completely
});
Press "" to save the code. Confirm with " y ", and confirm the name with "
". Raspberry Pi and Node.js WebSocket UI Now it is time add the HTML that allows for user input via WebSocket.
3 color sliders, one for each color (RGB)