LinkNode R4: Arduino-compatible WiFi relay controller

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Product Overview

LinkNode R4 is a WiFi relay controller and it is powered by ESP-12f ESP8266 WiFi module which is comptiable with Arduino programming. There are 4 relay channels and each channel allows you to control high-power devices (up to 10 A) via the on-board relay. LinkNode R4 can be used to remotely turn lights, fans and other devices on/off. The WiFi interface will allow you to associate the board with your existing WiFi network and send the commands over the network.

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  • ESP-12f ESP8266 WiFi module
  • 4 Channel relays,supporting:
    • 277V AC, 10A
    • 125V AC, 12A
  • 5V DC power
  • Two work modes:
    • Program via UART
    • Boot from flash
  • 4 indiator LEDs

LinkNode R4 Diagram


Control logic


How to use Android APP to control LinkNode R4

LinkNode R4 is an open source 4-Channel relay controller which is powered by the ESP8266 WiFi SoC.

Linker Nord R4.jpg

The following will introduce how to use Android APP to control the LinkNode R4.


1. Install Android and iOS APP

  • Download the APK file from the github and install it.
  • if your equipment is iphone/ipad,you can get the app form appstore and name is "LinkNode Relay".

2.Login LinkSpriteIO

  • If you never register an account on LinkSpriteIO, please enter Email and your password, then click the SIGN IN button
  • If you have an account on LinkSpriteIO, please enter Email and your password, then click the REGISTER button

LinkNode R4 1.png

3. Go to Relay device list

  • Click the plus icon on the upper right quarter to add a new LinkNode R4.

LinkNode R4 2.png

4.Scan the QRcode

  • Get the device information and register it to your account.

LinkNode R4 3.png

LinkNode R4 4.png

5.Configure to accece WiFi AP

  • Supply the power for LinkNodeR4, the LinkNode R4 will create a AP called LinkNodeAP
  • Use your mobile phone to connect this AP
  • Open a browser and enter the ip address and you will see the following website:

LinkNode R4 5.png

  • Click the button configure WiFi
  • Select your WiFi AP which you want to connect and enter your wifi password.
  • If connecting failed, you can go to the same website to configure it again.
  • After that, LinkNode R4 will connect to Linksprite IO via the internet.

6.Control your 4-channel relay

  • control the button on the right side to turn on or off the relays, and you can click the relay's name to change it.

LinkNode R4 6.png


1. Get started in Arduino programming

a. Requirements


** Hardware**
  • 5V/1A DC power is recommanded.
  • USB TTL UART cable

b. Install Arduino core for ESP8266


  • Open Boards Manager from Tools --> Board menu --> Boards Manager.


  • Search and install esp8266 platform (and don't forget to select your ESP8266 board from Tools --> Board menu after installation).


c. Check the configuration of Board

Because the LinkNode R4 has not been added into the offcial ESP8266 Arduino core repository yet, so you can't find this board on the boards list, but you can use the Generic ESP8266 Module, and select Flash Mode as QIO.


d. Create a Arduino Project

  • Enter the following source code and compile
 /*Turn on and off the S3 relay in every second */
 void setup()
 void loop()
   Serial.println("Relay ON\n");
   Serial.println("Relay OFF\n");

e. Test


  • Jump out the S5 on LinkNode R4 and select program via UART
  • Connect DC power to LinkNode R4
  • Connect USB TTL UART cable to UART port of LinkNode R4
  • Connnect the other side to PC
  • Check your serial port which your PC recognize
  • Click the **Upload* on Arduino IDE
  • After finished, jump out the S5 on LinkNode R4 and select boot from flash

2. Remotely control LinkNode R4 with LinkSprite.IO platform

LinkSprite IO is an IoT platform which supports RESTful API and WebSocket. These make the mobile APP, website application or device connect it very easily. The following I will introduce is about how to use LinkNode R4 to communicate with LinkSprite IO platform.

a. Create a new account and device on

Go to and sign up Enter your Email and password to create a new account Go to My Account to get your own API Key. The API Key is fatal because only add the Key in your codes, can the data sync to your IoTgo account.


  • Click My Device, and choose Create DIY Device.


  • Click the created device icon and get the DeviceID.


b. Query the source code using your own apikey and device ID

Device API which the LinkSprite IO support is JSON-based, which means all request and response data is enclosed in JSON format. Currently it supports 3 kind of request.

  • Update: Update device status to LinkSprite IO
  • Query: Get device status from LinkSprite IO

This demo will send http POST request to query the param--light on, if the light is on, then turn one relay on, if off, then turn off the relay.

c. Install WiFi Manager library

To make it more convinent, we add WiFi manager library in this demo.

The ESP8266 WiFi Connection manager with web captive portal, this Arduino library can make configure AP's SSID and password via web page when you want LinkNode R4 to connect to AP.

  • Open Arduino IDE and go to Sketch --> Include Library --> Manage Libraries
  • Search the wifimanager and install it


d. Develope source code

  • Enter the following source code
  • Configure your apikey and deviceID in the source code
   #include <ESP8266WiFi.h>
   #include <WString.h>
   //the library are needed for autoconfig WiFi
   #include <DNSServer.h>
   #include <ESP8266WebServer.h>
   #include <WiFiManager.h>       
   // replace with your own API key and device ID,
   String apikey = "xxxxxxxxxxxxxxxxxxxxxxxxxxxx";
   const char* deviceID="xxxxxxxxxxxxx";
  const char* server = "";
 WiFiClient client;
 void setup() {                
   pinMode(12, OUTPUT);
   WiFiManager wifiManager;
   wifiManager.setAPStaticIPConfig(IPAddress(10,0,1,1), IPAddress(10,0,1,1), IPAddress(255,255,255,0));
   Serial.print("WiFi Connected ...\n");
   Serial.println("WiFi connected");
 void loop() {
   if (client.connect(server,80)) {  
   String  postStr ="{";
           postStr +="\"action\":\"query\",";
           postStr +="\"apikey\":\"";
           postStr += apikey;
           postStr +="\",";
           postStr +="\"deviceid\":\"";
           postStr += deviceID;
           postStr +="\",";
           postStr += "\"params\":";
           postStr += "[";
           postStr += "\"light\"";
           postStr +="]";
           postStr +="}";
      client.print("POST /api/http HTTP/1.1\n");
      client.print("Host: ");
      client.print("\nContent-Type: application/json\n");
      client.print("Content-Length: ");
   Serial.println("Store response...");
   String request = "";
   while (client.available()) {
     char c =;
     request +=c;
 if (request!= NULL)
   int index1 = request.indexOf(":{");
   int index2 = request.indexOf("},");
   String param = request.substring(index1, index2 + 1);
   Serial.print("The param is ");
       digitalWrite(12, LOW);    
   } else if(param.indexOf("on")>0){
       digitalWrite(12, HIGH);    

e. Configure to accece WiFi AP

  • Take the step above to upload the program, the LinkNode R4 will create a AP called LinkNodeAP
  • Use your mobile phone to connect this AP
  • Open a browser and enter the ip address and you will see the following website:


  • Click the button configure WiFi
  • Select your WiFi AP which you want to connect and enter your wifi password.
  • If connecting failed, you can go to the same website to configure it again.
  • Also, you can use Serial Monitor in Arduino IDE to check the status.
  • After that, LinkNode R4 will connect to Linksprite IO via the internet.

f. Test

  • Open the serial monitor to check the status


  • Open your light device which is create on
  • Click the button ON and OFF
  • Check the status of relay on LinkNode R4, is it following your control?


LinkNode R4 Schematic


How to use Android APP to control Linknode R4

How to use IOS APP to control Linknode R4


(3 reviews) Write a Review

3 Reviews Hide Reviews Show Reviews

  • 1
    package never delivered

    Posted by gianluca terrana on 11th Nov 2017

    package never delivered - I can't test rate the product but only the service

  • 4
    Great for many projects!

    Posted by Unknown on 13th Sep 2017

    In the past month I've bought a few of these and used 2 to do some pretty fun projects, from a garage door opener to a winch controller. Very handy things. The only issue I have with them is a very technical issue with how they connect to wireless. If you have multiple SSID's on Cisco AP's, they won't connect unless they are either connecting to a broadcasting SSID, or, if NONE of the SSID's are broadcasting. It's pretty technical, but that's the only thing. My workaround was to just not broadcast any.

  • 5
    LinkNode R4 Tinkering Fun

    Posted by Unknown on 31st Jan 2017

    This little 4 relay WiFi device is great for all kinds of home automation projects. Fully supported by Arduino IDE. Hence easy to program, but even out of the box it is fully functional. Mind to get the latest app for your phone. Unfortunately the iPhone app seems to require a 64-bit iPhone; my 5c does not cut it. But there are many alternatives once the device is reprogrammed, e.g. to use a MQTT broker.