Node-RED is an open-source graphical development (drag & drop) tool created by Nick O'Leary from IBM that helps you rapidly create application, especially event-driven application like Internet of Things (IOT) applications. It is already pre-installed in Raspbian Stretch for Raspberry Pi, or it can be installed by using Node.js.
The main reason we use Node-RED in this tutorial is because it does not require a very hardcore programming knowledge. It is simply drag and drop block of function, we call it node and then we put them all together.

Hardware Requirements for this project:

1. Raspberry Pi 3 Model B
2. 8GB MicroSD Card
3. MicroSD Card Reader (for installation)
4. 4 Channel Relay
5. Breadboard
6. Resistor 220 Ohm x4
7. LED x 4 (Any color)
8. Screwdriver
9. Male to Male Wire Jumper x16
10. Female to Male Wire Jumper x8
11. Bluetooth keyboard & mouse
12. Monitor with HDMI cable + Micro USB Power Adapter
13. Long nose plier (Optional)

Step 1: Download Raspbian & Install Raspbian OS into Micro SD

*if you already have raspbian before, just skip this step.

• Download zipped Raspbian & Etcher from official website.
• Unzip raspbian folder
• Insert Micro SD to your computer
• Install etcher to your computer
• Once installed, run etcher it will look like below:
• Click button “Select Image” and choose raspbianOS.image file
• Make sure your MicroSD is selected, otherwise click “Change” and choose your MicroSD path.
• Hit button Flash and wait until finish. Once finish, safely remove the micro sd

Step 2: Assemble the wiring

Follow with these schematic:

Raspberry Pi Pin	4 Channel Relay
Pin 4 (5v Pin)	VCC/ +Ve
Pin 6 (GND)	GND /-Ve
Pin 35 (GPIO 19)	IN 1
Pin 37 (GPIO 26)	IN 2
Pin 38 (GPIO 20)	IN 3
Pin 40 (GPIO 21)	IN 4

Step 3: Let's node-red it

• Insert MicroSD into SD slot at Raspberry Pi.
• Plug in HDMI cable to HDMI port Raspberry Pi.
• Plug in the micro usb power adapter and switch on Raspberry Pi.
• Ensure your raspberry pi has internet connection.
• Open terminal by click the terminal icon at top left or press keyboard “Ctrl+Alt+T”
• Type “node-red-start” and copy the IP address shown in terminal
  
• Open web browser and paste/type the IP address that shown in terminal.
  *Tips: it better bookmarked it at your web browser.
  
• Before we start the magic, we need to install new palette in node-red
  node-red-contrib-gpio
node-red-contrib-ui_j

  • Click the burger menu on top right corner, then click “Manage Palette”
    

  • Select Install Tab, then search and install each the
    node-red-contrib-gpio & node-red-contrib-ui_j
    
    

  • Once finish install, click Close.

• Drag the “Switch” Node from ui category & “rpi-gpio-out” node from rpio category into Flow Panel.Rename each Switch node with naming convention for example Switch_1. Add Name of Group “Relay” for grouping the node for Web Design once deploy it. Set the On Value to 1 and Off Value to 0. For rpi-gpio out set all the Raspberry Pi Pin(Pin 35,Pin 37,Pin 38, Pin 40) from Step 2 except for 5V and GND Pin. Rename rpi-gpio pin to naming convention for example Pin_37. Then click Done button.
  
  
• Once finish the configuration for each node it will look like this:
  
  Then connect each node for example Switch_1 connect to Pin_35 this:
  
• Then click Deploy Button. It’ll show Deploy Successful.
  And you have it.
• Open new tab in browser copy and paste the ip address of node red and add /ui at the end for example: http://127.0.0.1:1880/ui
• Your website UI will look like this:
  

Extra: Auto start Node Red at every boot

• Open terminal
• Type “sudo system enable nodered.service”. Remove the “ ”, and hit Enter.
  Your node-red will auto start every time Raspberry Pi boots up.