Project Overview

This DIY IoT project shows you how to turn an Arduino Uno R4 + DHT11 sensor into a smart environmental monitor that automatically sends email alerts when the temperature exceeds a threshold. It leverages built-in Wi-Fi and the CircuitDigest Cloud Email API to deliver timely notifications straight to your inbox.

What You’ll Build

A wireless temperature alert system that:

  • Reads temperature & humidity with a DHT11 sensor.

  • Connects to the internet over Wi-Fi.

  • Sends structured alert emails when thresholds are crossed.

  • Avoids repeated alerts for the same event.Required Hardware

ComponentQty
Arduino Uno R41
DHT11 Temp & Humidity Sensor1
Breadboard1
Jumper WiresAs needed

The DHT sensor’s data pin goes to digital pin 2 with the internal pull-up resistor enabled, and 5V/GND power connects to the Arduino.

How It Works

  1. Startup & Sensor Setup: The sketch initialises the DHT11 and connects the Arduino to your Wi-Fi network.

  2. Continuous Monitoring: The Arduino reads temp/humidity at regular intervals.

  3. Threshold Check: If the temperature goes above your defined limit, the code formats a JSON payload and sends it via HTTPS POST to the CircuitDigest Cloud email endpoint.

  4. Email Alert: The cloud API takes care of delivering a formatted alert email to your address.

  5. Event Control: To prevent spamming, the system blocks repeated emails until conditions return to normal.

Key Code Concepts (Simplified)

Libraries & Sensor Setup

#include <WiFiS3.h>
#include <DHT.h>

#define DHTPIN 2
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);

  • Sets up Wi-Fi and DHT11 sensor support.

Network Credentials

const char* ssid = "yourSSID";
const char* password = "yourPassword";
const char* host = "www.circuitdigest.cloud";
const int port = 443;

  • Define your Wi-Fi and cloud API server details.

Temperature Logic

const float TEMP_THRESHOLD = 30.0;  // trigger point
...
if (temperature > TEMP_THRESHOLD) {  sendEmail(temperature, humidity);
}

  • When temp exceeds the threshold, trigger the email function.

Sending JSON Over HTTPS The sendEmail() function builds a JSON body with current sensor values and sends it securely to the cloud API, which then handles final email delivery.

Troubleshooting Tips

  • Wi-Fi Fails: Check SSID/password and serial monitor status.

  • Sensor Returns NaN: Ensure correct wiring and stable connections.

  • No Email Received: Validate API key, template ID, and email destination. Check spam/junk folders.

  • Too Many Alerts: Ensure flags and timing logic prevent frequent repeats.

Where You Can Use It

  • Server room safety alerts

  • Home environment monitoring

  • Greenhouse climate control

  • Cold storage oversight

  • IoT learning platforms

This Arduino Send Email Notifications shows how simple sensor data can be elevated into a connected alert system using cloud services — perfect for real-world IoT applications and community showcases. 

Explore 500+ Arduino Projects with code, circuits & step-by-step tutorials at CircuitDigest to spark your next DIY electronics idea.