IoT + Blockchain Integration: DHT22 Sensor Data on Cardano

A practical example of integrating IoT devices with blockchain technology. This project demonstrates how to read real-world sensor data from a DHT22 temperature/humidity sensor connected to Raspberry Pi 5, and store that data on-chain using the Cardano blockchain.

🎯 Project Overview

This repository provides a complete, working example of:

• IoT Data Collection: Reading temperature and humidity from DHT22 sensor via Raspberry Pi 5
• Real-time Monitoring: Continuous sensor data monitoring with auto-retry mechanism
• Blockchain Integration: Creating and submitting transactions to Cardano blockchain
• Data Immutability: Storing IoT sensor data permanently on-chain

Use Cases

• Environmental monitoring with tamper-proof data storage
• Supply chain temperature tracking
• Smart home automation with blockchain verification
• IoT device data provenance and audit trails

🔄 How It Works

      ┌─────────────────┐
      │   DHT22 Sensor  │ (Temperature & Humidity)
      │   GPIO 4, Pin 7 │
      └────────┬────────┘
               │
               ▼
┌─────────────────────────────────────┐
│    Raspberry Pi 5                   │
│  ┌───────────────────────────────┐  │
│  │  Python Script (read_dht22.py)│  │
│  │  • Read sensor via GPIO       │  │
│  │  • Return JSON data           │  │
│  └──────────┬────────────────────┘  │
│             │                       │
│             ▼                       │
│  ┌───────────────────────────────┐  │
│  │  Node.js (index.js)           │  │
│  │  • Collect sensor data        │  │
│  │  • Format for blockchain      │  │
│  │  • Auto retry on errors       │  │
│  └──────────┬────────────────────┘  │
└─────────────┼───────────────────────┘
              │
              ▼
┌─────────────────────────────────────┐
│    Cardano Blockchain               │
│  ┌───────────────────────────────┐  │
│  │  Transaction Submission       │  │
│  │  • Metadata: sensor readings  │  │
│  │  • Timestamp                  │  │
│  │  • Immutable storage          │  │
│  └───────────────────────────────┘  │
└─────────────────────────────────────┘

Data Flow

1. Sensor Reading: DHT22 sensor measures temperature and humidity
2. Data Collection: Raspberry Pi reads sensor data via GPIO pins
3. Data Processing: Node.js formats data into JSON structure
4. Transaction Creation: Data is embedded into Cardano transaction metadata
5. On-Chain Storage: Transaction is submitted to Cardano blockchain
6. Verification: Data is permanently stored and publicly verifiable

🚀 Quick Start

# 1. Install Python dependencies
sudo pip3 install rpi-lgpio adafruit-circuitpython-dht --break-system-packages

# 2. Install Node.js dependencies
npm install

# 3. Configure GPIO permissions (one-time setup)
sudo usermod -a -G gpio $USER
sudo reboot

# 4. Run IoT monitor
npm start

🔧 Hardware Setup

Components Required

• Raspberry Pi 5 (or any Raspberry Pi with GPIO)
• DHT22 Sensor (AM2302 - Temperature & Humidity sensor)
• Jumper Wires (3 wires: Power, Data, Ground)
• Optional: 10kΩ pull-up resistor for Data line

Wiring Diagram

DHT22 Sensor          Raspberry Pi 5
┌─────────┐           ┌──────────────┐
│    +    │ ────────► │ Pin 1 (3.3V) │
│         │           │              │
│  Data   │ ────────► │ Pin 7 (GPIO4)│
│         │           │              │
│    -    │ ────────► │ Pin 9 (GND)  │
└─────────┘           └──────────────┘

Connection Table

DHT22 Pin	Raspberry Pi Pin	GPIO	Description
+ (VCC)	Pin 1	3.3V	Power supply
Data	Pin 7	GPIO 4	Data signal
- (GND)	Pin 9	GND	Ground

⚠️ Important:

• Always use 3.3V, NOT 5V - Using 5V may damage your Raspberry Pi
• Power off Raspberry Pi before connecting/disconnecting sensors

📦 Installation

Prerequisites

• Hardware: Raspberry Pi 5 (or any model with GPIO)
• OS: Raspberry Pi OS (Debian-based)
• Node.js: v16.x or higher
• Python: 3.7 or higher
• Network: Internet connection for blockchain transactions

Step 1: Clone Repository

git clone <your-repo-url>
cd iot1

Step 2: Install System Dependencies

sudo apt-get update
sudo apt-get install -y python3 python3-pip build-essential python3-dev nodejs npm

Step 3: Install Python Libraries

# Install DHT22 sensor libraries
sudo pip3 install rpi-lgpio adafruit-circuitpython-dht --break-system-packages

Step 4: Install Node.js Dependencies

npm install

Step 5: Configure GPIO Permissions

To run without sudo, add your user to the gpio group:

sudo usermod -a -G gpio $USER
sudo reboot  # Required for group changes to take effect

Step 6: Configure Cardano Wallet (Optional)

If you want to submit transactions to Cardano blockchain, create a .env file:

# Copy example environment file
cp .env.example .env

# Edit .env with your credentials
nano .env

Add your Blockfrost API key and wallet mnemonic:

BLOCKFROST_API_KEY=your_blockfrost_api_key
MNEMONIC="your mnemonic phrase goes here"

How to get credentials:

• Blockfrost API Key: Sign up at blockfrost.io and create a project
• Mnemonic: Your 12/15/24-word wallet recovery phrase

⚠️ Security Warning: Never commit .env file to version control!

Step 7: Verify Installation

# Test sensor reading
python3 dht22.py
# Expected output: {"temperature": 23.9, "humidity": 78.6}

# Test with npm
npm test

# Verify GPIO permissions
groups | grep gpio

# Test Node.js environment
node --version
npm --version

💻 Usage Guide

This project provides 3 main operating modes:

1️⃣ Basic Mode: Sensor Data Monitoring

Purpose: Continuously read and display temperature/humidity data from DHT22 sensor.

How to run:

# Run continuous monitoring (reads every 0.5 seconds)
npm start

# Or run with auto-reload (for development)
npm run dev

Expected Output:

========================================
DHT22 Real-Time Sensor Monitor
========================================
Connection Details:
  Positive -> 3.3V (Pin 1)
  Out      -> GPIO 4 (Pin 7)
  Negative -> GND (Pin 9)
========================================
Read Interval: 3 seconds
Press Ctrl+C to stop
========================================

[8:15:48 PM] ✓ Reading #1 | Temp: 23.9°C | Humidity: 78.6%
[8:15:54 PM] ✓ Reading #2 | Temp: 23.9°C | Humidity: 78.1%
[8:15:58 PM] ✓ Reading #3 | Temp: 24.0°C | Humidity: 78.1%
[8:16:01 PM] ✓ Reading #4 | Temp: 23.9°C | Humidity: 78.1%

Stop the program: Press Ctrl+C

========================================
📊 Session Statistics
========================================
Total readings: 262
Successful: 260
Failed: 2
Success rate: 99.2%
========================================
DHT22 Monitor stopped
========================================

Symbol Explanations:

• ✓ : Successful reading
• ⟳ : Retrying due to temporary error
• ✗ : Failed after all retry attempts

---

2️⃣ One-time Read Mode

Purpose: Quick check of current sensor data.

# Using Python (direct)
python3 dht22.py
# Output: {"temperature": 23.9, "humidity": 78.6}

# Using Node.js wrapper
npm run ms
# Output: { temperature: 23.9, humidity: 78.7 }

# Or use npm test
npm test

When to use:

• Test if sensor is working
• Debug hardware connections
• Get quick values without continuous monitoring

---

3️⃣ Advanced Mode: Write Data to Blockchain

Purpose: Read sensor and write data to Cardano blockchain (automatically every 2 minutes).

Step 1: Check configuration

# Check if .env file has all required information
cat .env

The .env file must contain:

BLOCKFROST_API_KEY=preprod...your_key_here
MNEMONIC="word1 word2 word3 ... word12"

Step 2: Run blockchain write script

npm start -- --write

Expected Output:

╔══════════════════════════════════════════════════════════╗
║       📤 BLOCKCHAIN TRANSACTION - WRITE DATA           ║
╚══════════════════════════════════════════════════════════╝
⏰ Time: 11/4/2025, 8:15:48 PM

📡 Step 1/5: Reading sensor data...
   ✓ Temperature: 23.9°C
   ✓ Humidity: 78.6%

🔨 Step 2/5: Building transaction...
   • Sensor Name: dht22_01
   • Temperature (on-chain): 23900 (23.9°C × 1000)
   • Humidity (on-chain): 78600 (78.6% × 1000)

   ✓ Transaction built successfully

✍️  Step 3/5: Signing transaction...
   ✓ Transaction signed

📤 Step 4/5: Submitting to Cardano Preprod network...
   ✓ Transaction submitted!

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
🔗 Transaction Hash:
   a1b2c3d4e5f6789abcdef...

🌐 View on Explorer:
   https://preprod.cexplorer.io/tx/a1b2c3d4e5f6789abcdef...
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

⏳ Step 5/5: Waiting for blockchain confirmation...
   ✓ Transaction confirmed on blockchain!

✅ SUCCESS: Data written to Cardano blockchain
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

⏰ Next submission in 2 minutes...

Data stored on blockchain:

// Data format in smart contract
{
  sensorName: 'dht22_01',
  temperature: 23900,  // = 23.9°C × 1000
  humidity: 78600      // = 78.6% × 1000
}

View transaction on blockchain:

• Testnet (Preprod): https://preprod.cexplorer.io/tx/YOUR_TX_HASH
• Mainnet: https://cexplorer.io/tx/YOUR_TX_HASH

Important Notes:

• Script runs continuously every 2 minutes
• Each transaction costs ~0.2 ADA gas fee
• Ensure wallet has sufficient ADA balance (minimum 2-3 ADA)
• Data is stored permanently on blockchain and cannot be deleted

---

4️⃣ Read Data from Blockchain

Purpose: View historical sensor data stored on blockchain.

# Monitor blockchain data (updates every 30 seconds)
npm run monitor

Expected Output:

╔══════════════════════════════════════════════════════════╗
║       � BLOCKCHAIN QUERY - READ DATA                  ║
╚══════════════════════════════════════════════════════════╝

�🔍 Querying Cardano blockchain...
   • Sensor: dht22_01
   • Policy ID: d5e6f7a8b9c0d1e2f3...

� Fetching transactions...
   ✓ Found 145 transactions

⚙️  Processing transaction data...
   • Processed 10/145 transactions...
   • Processed 20/145 transactions...
   ...
   • Processed 140/145 transactions...
   ✓ Successfully processed 145 records

✅ Query completed successfully
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

📊 Showing 5 most recent records:

📝 Record #141
   Time: 11/4/2025, 8:00:00 PM
   Temperature: 23.8°C
   Humidity: 78.5%
   Transaction: https://preprod.cexplorer.io/tx/abc123...

📝 Record #142
   Time: 11/4/2025, 8:02:00 PM
   Temperature: 23.9°C
   Humidity: 78.6%
   Transaction: https://preprod.cexplorer.io/tx/def456...

[... 3 more records ...]

⏰ Refreshing in 30 seconds...

---

5️⃣ Auto Retry Feature

The system automatically retries when sensor read errors occur:

Successful retry example:

[8:20:10 PM] ⟳ Retry 1/5 - Sensor timeout
[8:20:12 PM] ⟳ Retry 2/5 - Timed out waiting for PulseIn on START
[8:20:14 PM] ✓ Reading #5 | Temp: 23.9°C | Humidity: 78.6%
   └─ Success after 2 retries

Failed retry example:

[8:20:20 PM] ⟳ Retry 1/5 - Sensor timeout
[8:20:22 PM] ⟳ Retry 2/5 - No response
[8:20:24 PM] ⟳ Retry 3/5 - Timeout
[8:20:26 PM] ⟳ Retry 4/5 - RuntimeError
[8:20:28 PM] ⟳ Retry 5/5 - Sensor timeout
[8:20:30 PM] ✗ Failed after 5 attempts: Sensor communication error

Retry configuration:

• Maximum retry attempts: 5 times
• Delay between retries: 2 seconds
• Maximum total timeout: ~12 seconds

---

📋 Command Summary

Command	Purpose	Runs Forever?
npm run write	Write to blockchain	✅ Yes (every 2 min)
npm run monitor	Read from blockchain	✅ Yes (every 30s)
npm run sensor	Test sensor directly	❌ No

---

Blockchain Submission Interval

Edit write.ts to change how often data is submitted to blockchain:

const intervalMs = 2 * 60 * 1000; // Current: 2 minutes
// const intervalMs = 5 * 60 * 1000;  // 5 minutes
// const intervalMs = 10 * 60 * 1000; // 10 minutes

GPIO Pin Configuration

Edit dht22.py to use a different GPIO pin:

board_pin = board.D4  # Current: GPIO 4 (Pin 7)
# board_pin = board.D17  # GPIO 17 (Pin 11)
# board_pin = board.D27  # GPIO 27 (Pin 13)

Blockchain Configuration

Configure blockchain settings in .env file:

# Blockfrost API (Get from https://blockfrost.io)
BLOCKFROST_API_KEY=your_blockfrost_api_key

# Wallet Mnemonic (24 words)
MNEMONIC="your mnemonic phrase goes here"

Blockfrost vs Local Node:

• Blockfrost (Recommended): Easy API access, no node setup required
• Local Node: More decentralized, requires running cardano-node

🐛 Troubleshooting

Sensor Issues

Problem: ModuleNotFoundError: No module named 'adafruit_dht'

sudo pip3 install rpi-lgpio adafruit-circuitpython-dht --break-system-packages

Problem: Permission denied (GPIO access)

sudo usermod -a -G gpio $USER
sudo reboot

# Verify group membership
groups | grep gpio

Problem: Failed to read sensor after 5 attempts

Check the following:

• ✓ Verify wiring connections (especially Data pin to GPIO 4)
• ✓ Confirm using 3.3V, NOT 5V
• ✓ Increase READ_INTERVAL to 5000ms or higher
• ✓ Try different GPIO pin (GPIO 17, 27)
• ✓ Restart Raspberry Pi
• ✓ Test with: python3 dht22.py or npm test

Problem: RuntimeError: Timed out

This is normal for DHT22 sensors. The script will auto-retry. If persistent:

# Check power supply (undervoltage can cause issues)
vcgencmd get_throttled

# Check CPU temperature (overheating can affect GPIO)
vcgencmd measure_temp

# Test sensor directly
python3 dht22.py

# Try reading multiple times
for i in {1..5}; do python3 dht22.py; sleep 3; done

Blockchain Issues

Problem: Transaction submission failed

Check:

• ✓ .env file exists with valid BLOCKFROST_API_KEY and MNEMONIC
• ✓ Blockfrost API key is for correct network (testnet/mainnet)
• ✓ Wallet has sufficient ADA balance (min 2 ADA for testnet)
• ✓ Mnemonic phrase is correct (12/15/24 words)
• ✓ Network connectivity to Blockfrost API

Problem: Invalid metadata format

Ensure sensor data is valid JSON:

# Test sensor output
python3 dht22.py | jq .

# Expected output:
# {
#   "temperature": 23.9,
#   "humidity": 78.6
# }

📁 Project Structure

iot1/
├── index.ts              # Main sensor monitoring application
├── write.ts              # Blockchain data submission script
├── read.ts               # Read blockchain data
├── read-sensor.ts        # Simple sensor reading script
├── dht22.py              # Python script for DHT22 sensor (GPIO)
├── sensor.ts             # TypeScript sensor interface
├── package.json          # Node.js dependencies
├── tsconfig.json         # TypeScript configuration
├── plutus.json           # Cardano smart contract config
├── .env                  # Environment variables (Blockfrost, mnemonic)
├── .env.example          # Environment template
├── action/               # Blockchain transaction handlers
│   ├── claim.ts          # Claim transaction logic
│   ├── read.ts           # Read on-chain data
│   └── write.ts          # Write data to blockchain
├── scripts/              # Smart contract utilities
│   ├── index.ts          # Contract exports
│   └── mesh.ts           # Cardano Mesh SDK integration
└── README.md             # This documentation

Key Files

• index.ts: Main monitoring app - reads sensor every 3 seconds with retry mechanism
• write.ts: Submits sensor data to Cardano blockchain every 2 minutes
• dht22.py: Python script that interfaces with DHT22 via GPIO 4
• sensor.ts: TypeScript wrapper for Python sensor communication
• read-sensor.ts: Simple one-time sensor reading script
• action/write.ts: Creates and submits Cardano transactions with sensor data
• action/read.ts: Queries blockchain for historical sensor data
• scripts/mesh.ts: Smart contract wrapper using Mesh SDK
• plutus.json: Smart contract configuration for on-chain validation
• .env: Stores Blockfrost API key and wallet mnemonic (never commit!)

🔍 How Blockchain Integration Works

Transaction Creation Process

1. Read Sensor Data: Node.js calls Python script to read DHT22
2. Format Metadata: Sensor data is formatted as Cardano transaction metadata
3. Build Transaction: Use Cardano SDK to construct transaction with metadata
4. Sign Transaction: Sign with wallet private key
5. Submit to Network: Broadcast to Cardano blockchain
6. Confirmation: Wait for transaction confirmation

Querying On-Chain Data

// Example: Read historical sensor data from blockchain
import { readSensorData } from './action/read';

const txHash = "abc123...";
const sensorData = await readSensorData(txHash);
console.log(sensorData);

System Diagnostics

# Check GPIO status
gpio readall

# Monitor CPU temperature
watch vcgencmd measure_temp

# Check power supply status
vcgencmd get_throttled

# View system logs
journalctl -f

🎓 Learning Resources

IoT & Raspberry Pi

• Raspberry Pi GPIO Documentation
• DHT22 Sensor Datasheet
• Adafruit DHT Library Guide

Cardano Blockchain

• Cardano Documentation
• Cardano Developer Portal
• Mesh SDK Documentation
• Transaction Metadata Standard

Example Use Cases

• Supply chain temperature monitoring
• Environmental data marketplaces
• Decentralized sensor networks
• IoT device authentication

🤝 Contributing

Contributions are welcome! Please feel free to submit pull requests or open issues.

📄 License

ISC

🔐 Security Notes

• Never commit .env file to version control - Add to .gitignore
• Never share your mnemonic phrase with anyone
• Use Blockfrost API keys with appropriate permissions
• Store mnemonic securely (consider hardware wallets for mainnet)
• Test on Cardano testnet before mainnet deployment
• Regularly update dependencies for security patches
• Monitor transaction costs and wallet balance on mainnet
• Use separate wallets for testing and production

⚡ Performance Tips

• Batch multiple readings into single blockchain transaction to save fees
• Use local Cardano node for faster transaction submission
• Implement data validation before submitting to blockchain
• Consider using IPFS for large data payloads (store hash on-chain)

📞 Support

For questions or issues:

• Open an issue on GitHub
• Check Troubleshooting section
• Review Cardano Stack Exchange

---

Built with ❤️ using Raspberry Pi 5 and Cardano Blockchain