Introduction
In this guide, you’ll learn how to connect an ESP32-WROOM-32 (38 Pin) development board to AWS IoT Core using the MQTT protocol. You’ll also control a 2-Channel Relay Module with optocoupler to switch devices remotely via the cloud. This is a perfect starting point for building smart home systems, industrial IoT projects, or remote device management solutions.
By the end of this tutorial, you will:
- Set up AWS IoT Core for secure device communication.
- Program the ESP32 to communicate via MQTT.
- Control relays connected to the ESP32 from AWS.
Prerequisites
Before you get started with AWS IoT Core and ESP32, make sure you have the following:
Creating and Configuring a Thing in AWS IoT Core:
- Basic Knowledge of MQTT Protocol
Understanding of MQTT topics, publish/subscribe model, and message handling. - ESP32-WROOM-32 (38 Pin) Development Board
A compatible ESP32 board for connecting to AWS IoT Core. - 2-Channel Relay Module with Optocoupler
To control external devices or appliances via the ESP32. - Active AWS Account
Necessary for creating IoT Things, certificates, and policies on AWS IoT Core. - Latest Arduino IDE Installed
Required for writing, compiling, and uploading code to the ESP32 board.
Start by logging into your AWS Management Console with the root user credentials. This guide assumes that your AWS account has already been created.
✅ If you’re a new user and need help setting up an AWS account from scratch, we’ll cover that in a detailed article soon.
🎥 Meanwhile, follow this video to quickly create your AWS account step by step!
Search for IoT Core:
Select AWS IoT Core and Click on Things:
Click on create things:
Click on create single thing:
Understanding AWS IoT Shadows: No Shadow, Named Shadow, and Unnamed (Classic) Shadow
When you create a Thing in AWS IoT Core, you can choose how its state (shadow) will be managed. Device Shadows allow AWS IoT Core to store the device’s last reported and desired states, even when the device is offline. Here’s a quick overview of the available options:
1. No Shadow
If you select this option, AWS IoT Core will not maintain any shadow document for the device. The device must handle state management entirely through direct communication (such as MQTT messages). This is suitable for devices that do not require state persistence.
2. Unnamed (Classic) Shadow
Also known as the default shadow, the unnamed or classic shadow provides a single JSON document that represents the entire device state. This is ideal for simpler devices where one shadow is enough to reflect the device’s status, commands, and configuration.
3. Named Shadow
Named shadows allow you to create multiple shadow documents for the same Thing. This is useful for complex devices with multiple components — for example, a smart home device that manages both a thermostat and a light system can have separate named shadows for each component.
For This Tutorial: Selecting ‘No Shadow’ for Simplicity
In this guide, we will choose the ‘No Shadow’ option to keep the setup simple. This means AWS IoT Core will not maintain a Device Shadow for our Thing, and all device state management will rely on direct communication (such as MQTT messages). This approach is suitable for basic use cases or when shadow functionality is not required.
Assigning a Thing Name and Keeping Default Settings
For this example, set the Thing Name as “ESP32” to represent your IoT device. Leave all other settings at their default values to simplify the configuration process. This ensures a quick and hassle-free setup, especially suitable for beginners or testing purposes.
Generate Certificates with Default Settings
In the next step, choose the option to automatically generate a new certificate and keep all other settings at their default values. AWS IoT Core will create a certificate and private key pair for your Thing, which is essential for secure device authentication and communication.
After the certificates are generated, be sure to download them for future use, as they won’t be accessible later.
Skip Policy Attachment for Now and Create the Thing
For this tutorial, we will not attach any policy at this stage. Policies define permissions for your device, but we will create and attach a policy separately in a later step.
Simply click on “Create Thing” to complete the process. Your AWS IoT Thing (named ESP32) will now be created with default settings and a generated certificate.
Download All Certificates for Future Use
Once the Thing is created, make sure to download all the generated certificates and the private key file. These files are essential for establishing a secure connection between your ESP32 device and AWS IoT Core. Without these certificates, the ESP32 will not be able to authenticate and communicate with AWS IoT services.
Creating an AWS IoT Policy for ESP32
When creating the policy, use the following JSON policy document. This policy grants the required permissions to your ESP32 device for connecting, publishing, subscribing, and receiving messages in AWS IoT Core:
In left side panel go to Security->Policies->Create Policy and select JSON
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"iot:Connect",
"iot:Publish",
"iot:Subscribe",
"iot:Receive"
],
"Resource": "*"
}
]
}
⚠️ Important:
This policy provides full access to AWS IoT Core resources ("Resource": "*"). For production environments, it’s recommended to restrict this to specific IoT Things or topics to ensure better security.
Attach the Policy to the Thing’s Certificate
Now that the IoT Policy has been created, the next step is to attach it to the certificate associated with your ESP32 Thing. This allows your device to securely communicate with AWS IoT Core using the permissions defined in the policy.
Steps to Attach the Policy:
- Go to the AWS IoT Core Console.
- In the left sidebar, navigate to Security → Certificates.
- Find the certificate you created earlier (associated with the ESP32 Thing).
- Click on the certificate ID to open its details.
- Under “Actions”, click “Attach policy”.
- From the list, select the policy you just created (e.g.,
ESP32_Policy) and click “Attach”.
✅ Now your ESP32 certificate is authorized to connect and interact with AWS IoT Core.
Note Down the Device Endpoint
Carefully note down the AWS IoT Device Endpoint URL, as this will be required later when configuring your ESP32 to securely connect to AWS IoT Core.
You can find this endpoint in the AWS IoT Core Console under AWS Console → Connect -> Domain Configurations
🔌 Connecting 5V Relay Module to ESP32 (Using GPIO13)
| ESP32 Pin | Relay Module Pin | Function |
|---|---|---|
| V5 (5V) | VCC | Power supply for the relay module |
| GPIO13 (G13) | IN1 | Relay control input |
| GND | GND | Common ground connection |
Steps to Connect ESP32 to AWS IoT Core
- const char WIFI_SSID[] = “Change This”;
- const char WIFI_PASSWORD[] = “Change This”;
- const char AWS_IOT_ENDPOINT[] = “Use this from previous step”; //change this
- // Amazon Root CA 1
static const char AWS_CERT_CA[] PROGMEM = R"EOF(
-----BEGIN CERTIFICATE-----
Replace with AWS CA1
-----END CERTIFICATE-----
)EOF";- // Device Certificate //change this
static const char AWS_CERT_CRT[] PROGMEM = R"KEY(
-----BEGIN CERTIFICATE-----
Replace with device certificate
-----END CERTIFICATE-----
)KEY";- // Device Private Key //change this
static const char AWS_CERT_PRIVATE[] PROGMEM = R"KEY(
-----BEGIN RSA PRIVATE KEY-----
Replace with device private key
-----END RSA PRIVATE KEY-----
)KEY";Upload the ESP32 Sketch After Updating Required Details
Use the following ESP32 Arduino sketch to connect your device to AWS IoT Core. Before uploading, make sure to update the placeholders with your specific AWS IoT credentials:
- Wi-Fi SSID and Password
- AWS IoT Endpoint URL
- Root CA Certificate
- Device Certificate
- Private Key
⚠️ Important: Replace the placeholder values with the actual credentials and endpoint you obtained from AWS IoT Core.
#include <Arduino.h>
#include "WiFi.h"
#include <WiFiClientSecure.h>
#include <PubSubClient.h>
#include <pgmspace.h>
const char WIFI_SSID[] = "--------"; //change this
const char WIFI_PASSWORD[] = "-------"; //change this
const char AWS_IOT_ENDPOINT[] = "--------"; //change this
// Amazon Root CA 1
static const char AWS_CERT_CA[] PROGMEM = R"EOF(
-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----
)EOF";
// Device Certificate //change this
static const char AWS_CERT_CRT[] PROGMEM = R"KEY(
-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----
)KEY";
// Device Private Key //change this
static const char AWS_CERT_PRIVATE[] PROGMEM = R"KEY(
-----BEGIN RSA PRIVATE KEY-----
-----END RSA PRIVATE KEY-----
)KEY";
#define THING_NAME "ESP32"
#define MQTT_PACKET_SIZE 1024
WiFiClientSecure net = WiFiClientSecure();
PubSubClient client(net);
#define LIGHT 13
const char publishShadowUpdate[] = "$aws/things/" THING_NAME "/shadow/update";
char publishPayload[MQTT_PACKET_SIZE];
void updateThing() {
strcpy(publishPayload, "{\"state\": {\"reported\": {\"powerState\":\"ON\"}}}");
publishMessage(publishShadowUpdate, publishPayload);
}
char *subscribeTopic[1] = {
"$aws/things/" THING_NAME "/command/light"
};
void connectAWS() {
int time_connect = millis();
WiFi.mode(WIFI_STA);
WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
Serial.println("Connecting to Wi-Fi");
while (WiFi.status() != WL_CONNECTED && millis() - time_connect < 60000) {
Serial.print("#");
}
if (WiFi.status() != WL_CONNECTED && millis() - time_connect > 60000) {
WiFi.disconnect();
Serial.print("Disconnected WiFi ..");
return;
}
configTime(19800, 0, "pool.ntp.org"); // For India time zone (GMT+5:30)
while (time(nullptr) < 100000) {
delay(100);
Serial.print(".");
}
Serial.println("\nTime synchronized!");
// Configure WiFiClientSecure to use the AWS IoT device credentials
net.setCACert(AWS_CERT_CA);
net.setCertificate(AWS_CERT_CRT);
net.setPrivateKey(AWS_CERT_PRIVATE);
// Connect to the MQTT broker on the AWS endpoint we defined earlier
client.setServer(AWS_IOT_ENDPOINT, 8883);
// Create a message handler
client.setCallback(messageHandler);
Serial.println("Connecting to AWS IOT");
if (WiFi.status() == WL_CONNECTED)
Serial.print("WiFi Connected!");
while ((WiFi.status() == WL_CONNECTED) && (!client.connect(THING_NAME))) {
Serial.print("*");
}
if (!client.connected()) {
Serial.println("AWS IoT Timeout!");
return;
}
// Subscribe to a topic
for (int i = 0; i < 1; i++) {
client.subscribe(subscribeTopic[i]);
Serial.println(subscribeTopic[i]);
}
Serial.println("AWS IoT Connected!");
}
void publishMessage(const char *topic, char *payload) {
client.publish(topic, payload);
Serial.print("Published [ ");
Serial.print(" ");
Serial.print(topic);
Serial.print("] ");
Serial.println(payload);
}
void handle_mqtt_msg(char *topic, byte *payload, unsigned int length) {
char resp[60] = { 0 };
if (strstr(topic, "$aws/things/" THING_NAME "/command/light")) {
if (strstr((const char *)payload, "light-on") != NULL) {
digitalWrite(LIGHT, LOW);
Serial.println("relay_update(LIGHT,LOW)");
} else if (strstr((const char *)payload, "light-off") != NULL) {
digitalWrite(LIGHT, HIGH);
Serial.println("relay_update(LIGHT,HIGH)");
} else {
Serial.println("relay_update(LIGHT,INVALID)");
}
} else {
Serial.println("Invalid: command");
}
}
void messageHandler(char *topic, byte *payload, unsigned int length) {
Serial.print("Message arrived [");
Serial.print(topic);
Serial.print("] ");
for (int i = 0; i < length; i++) {
Serial.print((char)payload[i]);
}
handle_mqtt_msg(topic, payload, length);
Serial.println();
}
void wifi_setup() {
connectAWS();
}
void setup() {
pinMode(LIGHT, OUTPUT);
digitalWrite(LIGHT, HIGH);
delay(1000);
Serial.begin(115200);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}
delay(3000);
wifi_setup();
}
void mqtt_task_update() {
static uint32_t now, last_sent;
if (!client.connected()) {
connectAWS();
}
now = millis();
if (now - last_sent > 1000 * 60) {
char msg[60] = { 0 };
sprintf(msg, "{ \"message\": \"Hello from ESP 32\" }");
publishMessage("MessageFromESP32", msg);
last_sent = now;
}
client.loop();
}
void loop() {
mqtt_task_update();
}
AWS IoT Topic and Message Structure for Relay Control
| MQTT Topic | Message Payload | Action Performed |
|---|---|---|
$aws/things/ESP32/command/light | light-on | Turns the relay (light) ON |
$aws/things/ESP32/command/light | light-off | Turns the relay (light) OFF |
To turn on the relay, send below command and message
To turn off the relay send below command and message
