This project shows how to send real-time Arduino WhatsApp notifications via WiFi without a GSM module or the complex official WhatsApp Business API. Instead, it leverages the CircuitDigest Cloud WhatsApp API to handle messaging so your board just sends simple HTTPS POST requests — perfect for IoT alerts like proximity warnings or other sensor triggers.

🎯 Overview

You’ll build a system where:

1. An ultrasonic sensor (HC-SR04) reads distance.

2. The Arduino UNO R4 WiFi connects to your WiFi network.

3. When a threshold is crossed (e.g., object within 20 cm), the board sends a JSON payload containing your recipient number, template ID, and sensor data to CircuitDigest Cloud.

4. The cloud service formats the message using a predefined WhatsApp template and delivers it to your registered WhatsApp number.

Key advantage: Your Arduino never talks to WhatsApp directly — CircuitDigest Cloud manages formatting, compliance, and delivery.

📦 What You Need

• Arduino UNO R4 WiFi

• HC-SR04 Ultrasonic Distance Sensor

• Breadboard + jumper wires

• USB cable to program the board

• Free API key from CircuitDigest Cloud

🔧 Wiring (HC-SR04 ↔ Arduino)

The sensor measures distance by sending a pulse (TRIG) and timing the echo return (ECHO).

☁️ Setup the CircuitDigest Cloud

1. Create an account at CircuitDigest Cloud and log in.

2. Go to API Key in your profile and generate a new key.

3. In the WhatsApp Notification API section, register up to 5 phone numbers to receive alerts. Each number must be verified via OTP.

4. Choose or note a WhatsApp template ID for your alert — templates contain placeholders like {#var#} that are filled with sensor data.

🧠 How It Works

• Arduino reads sensor data and checks if it crosses your defined threshold.

• If triggered and enough time has passed since the last alert, it builds a JSON payload with your phone number, template ID, and sensor values.

• This payload is sent through a secure connection to the CircuitDigest Cloud API.

• The service inserts your values into the chosen template and sends the WhatsApp message instantly.

🛠️ Arduino Logic (Simplified)

Core loop:

• Trigger ultrasonic pulse

• Read echo and calculate distance

• If distance < threshold and cooldown expired → send alert

Sending alerts:

• Connect to www.circuitdigest.cloud over HTTPS

• Build JSON with variables

• Post to /api/v1/whatsapp/send with your API key

• Log the server response for debugging.

💡 Example Payload

Here’s how a WhatsApp notification payload might look for a distance threshold alert:

{  "phone_number": "919876543210",  "template_id": "threshold_violation_alert",  "variables": {    "device_name": "Arduino R4 Distance Monitor",    "parameter": "Distance",    "measured_value": "15 cm",    "limit": "20 cm",    "location": "Parking Zone"  }
}

Customize values to fit your application.

📲 Flashing & Testing

1. Install the Arduino IDE and add support for the UNO R4 WiFi board.

2. Update SSID, WiFi password, API key, and recipient number in the sketch.

3. Upload the sketch and open Serial Monitor at 115200 baud.

4. Trigger the sensor to test alerts and watch WhatsApp messages arrive.

🧠 Tips for Hackaday Readers

• You can reuse this approach with other sensors (temperature, humidity, gas) — just replace the condition logic.

• The same API can send SMS or emails for broader notification options.

• Ensure you honor the API limit: max 100 messages per month and only verified numbers receive alerts.

🚀 What’s Next?

Extend this project by adding web dashboards, additional sensor nodes, or integrating other notification channels like SMS or email using the same cloud API backend — enabling robust monitoring without complex server infrastructure.

Discover 500+ Arduino projects with complete code, circuit diagrams, and step-by-step tutorials...