Hardware SMS API with SIM800L and Flask

Overview

This project is a hardware-based SMS API using the SIM800L GSM module for sending SMS and a Flask REST API for managing authentication, API keys, and logging. Key features include:

• SIM800L module for SMS transmission
• UART communication between SIM800L and a microcontroller/PC
• Flask API with authentication
• SQLite3 database for user and API key storage
• Logging system to track API requests
• Error handling for hardware troubleshooting
• Admin dashboard to manage API keys and apps

Hardware Setup

Components Used

• SIM800L GSM Module
• ESP32/Raspberry Pi for UART communication
• CP2102 USB-to-TTL adapter
• Power supply (3.7V Li-ion or 5V with a step-down to 4.2V)
• Antenna for better GSM signal reception

Wiring Diagram

Software Implementation

Flask API

The Flask-based backend provides endpoints for:

• /login - User authentication
• /dashboard - App management UI
• /api/sendsms - Sends SMS using an API key
• /apps/create - Generates new API keys for apps

SQLite3 Database

Stores:

• Users (with hashed passwords)
• Apps (each assigned a unique API key)
• API logs (to monitor requests and errors)

Web Interface

Login Page

Dashboard

• View a list of API apps
• Generate new API keys
• Access API documentation

API Documentation

Hardware Troubleshooting

The system logs SIM800L errors and provides details on possible causes:

• +CME ERROR: SIM not inserted - Ensure the SIM card is properly seated and not locked by a PIN.
• +CME ERROR: No network service - Check the antenna connection, signal strength, and network coverage.
• +CMS ERROR: Message failed - Verify the recipient’s phone number, available SMS credits, and proper UART configuration.

API Usage

The /api/sendsms endpoint requires an API key and a JSON request:

{
  "api_key": "your_api_key",
  "phone": "+1234567890",
  "message": "Hello, this is a test SMS!"
}

Response:

{
  "status": "success",
  "message": "SMS sent successfully"
}

Conclusion

This project offers a secure and scalable SMS solution by integrating Flask, SQLite3, and SIM800L with error logging and API key management. Future improvements may include Twilio integration, multi-user support, and better error diagnostics.

Author

HAMZAOUI —