Networking: Two ESP32C3 Boards Communicating Over Wi-Fi
For this week, I wanted to make two Seeed XIAO ESP32C3 boards communicate over Wi-Fi. The goal was to have one board (the server) read a switch state and send that information to the other board (the client), which would turn a green or red LED on based on the switch status.
Initially, I tried using my phone as a hotspot, but I ran into connectivity issues—some phone hotspots prevent devices from seeing each other on the same network. Instead, I used my laptop’s hotspot (PACO_LAPTOP) with a simpler IP configuration that allowed the boards to communicate freely. The sketches below show how each board is set up.
Client (Receiver) Code
This code connects to the hotspot and periodically makes an HTTP GET request to the server’s IP to fetch the switch status (ON or OFF). Depending on the response, it turns either the green or red LED on.
#include <WiFi.h>
// Replace with your Wi-Fi credentials
const char* ssid = "PACO_LAPTOP";
const char* password = "12345678";
// IMPORTANT: Set this to the IP address shown by Board #1’s Serial Monitor
const char* serverIP = "192.168.137.81";
const uint16_t serverPort = 80; // Same port we used in Board #1
// Pins for the LEDs
const int greenLedPin = D1; // Adjust if your board has different pin mappings
const int redLedPin = D4;
void setup() {
Serial.begin(115200);
pinMode(greenLedPin, OUTPUT);
pinMode(redLedPin, OUTPUT);
digitalWrite(greenLedPin, LOW);
digitalWrite(redLedPin, LOW);
// Connect to the Wi-Fi network
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
// Wait until connected
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println();
Serial.println("WiFi connected!");
Serial.print("Client IP address: ");
Serial.println(WiFi.localIP());
}
void loop() {
// Periodically get the switch status from Board #1
String switchStatus = getSwitchStatus();
// Check result and set LEDs accordingly
if (switchStatus == "ON") {
digitalWrite(greenLedPin, HIGH);
digitalWrite(redLedPin, LOW);
Serial.println("Switch is ON, showing GREEN.");
} else {
digitalWrite(greenLedPin, LOW);
digitalWrite(redLedPin, HIGH);
Serial.println("Switch is OFF, showing RED.");
}
delay(2000); // Wait 2 seconds between checks
}
String getSwitchStatus() {
WiFiClient client;
if (!client.connect(serverIP, serverPort)) {
Serial.println("Connection to server failed!");
return "";
}
// Send an HTTP GET request
client.print(String("GET / HTTP/1.1\r\n") +
"Host: " + serverIP + "\r\n" +
"Connection: close\r\n\r\n");
// Wait for the server to respond
unsigned long timeout = millis();
while (client.available() == 0) {
if (millis() - timeout > 2000) {
Serial.println(">>> Client Timeout !");
client.stop();
return "";
}
}
// Read the response
String response;
while (client.available()) {
response += client.readStringUntil('\\r');
}
client.stop();
// Check if "ON" or "OFF" is in the response
if (response.indexOf("ON") >= 0) {
return "ON";
} else if (response.indexOf("OFF") >= 0) {
return "OFF";
}
return "";
}
Server (Transmitter) Code
This code also connects to the hotspot, but instead of requesting data, it listens for an incoming HTTP request on port 80. It reads the switch state (using an internal pull-up on D1) and returns ON or OFF as text to the client.
#include <WiFi.h>
// Replace these with your Wi-Fi credentials
const char* ssid = "PACO_LAPTOP";
const char* password = "12345678";
// Start an HTTP server on port 80
WiFiServer server(80);
// Use the pin number for the switch
const int switchPin = D1;
// We'll track the last-known state of the switch
int lastSwitchState;
void setup() {
Serial.begin(115200);
pinMode(switchPin, INPUT_PULLUP); // Switch, with internal pull-up
// Initialize lastSwitchState
lastSwitchState = digitalRead(switchPin);
// Connect to Wi-Fi
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
// Wait until connected
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println();
Serial.println("WiFi connected!");
// Start the server
server.begin();
// Print the IP address
Serial.print("Server IP address: ");
Serial.println(WiFi.localIP());
}
void loop() {
// Detect switch changes and print to Serial
int currentSwitchState = digitalRead(switchPin);
if (currentSwitchState != lastSwitchState) {
lastSwitchState = currentSwitchState;
if (currentSwitchState == LOW) {
Serial.println("Switch changed to ON");
} else {
Serial.println("Switch changed to OFF");
}
}
// Handle any incoming client requests
WiFiClient client = server.available();
if (!client) {
return; // No client? nothing to do
}
// Wait until the client sends some data
while(!client.available()){
delay(1);
}
// Read the request
String request = client.readStringUntil('\\r');
client.flush();
// Determine switch state
String switchStatus = (currentSwitchState == LOW) ? "ON" : "OFF";
// Send an HTTP response
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/plain");
client.println("Connection: close");
client.println();
client.println(switchStatus);
// Close the connection
client.stop();
}
Once both boards are connected to the same hotspot, the client will regularly send an HTTP request to the server’s IP address on port 80. The server responds with “ON” or “OFF,” depending on the switch state. The client then lights up the appropriate LED and logs the status to the Serial Monitor.
Below is a short video demonstration of the boards in action: