⛓️ Blockchain in IoT — Demo

A real-time demo of a Raspberry Pi Pico W publishing LM35 temperature readings to a Hardhat local blockchain, with a live web dashboard showing every reading as it lands on-chain.

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Architecture

┌─────────────────────┐      HTTP POST       ┌─────────────────────────┐
│  Raspberry Pi Pico W│  ────────────────►  │   Relay Server          │
│  (LM35 + MicroPy)  │  /reading            │   relay/server.js       │
└─────────────────────┘                      │   localhost:3000        │
                                             └──────────┬──────────────┘
                                                        │  ethers.js
                                                        ▼
                                             ┌─────────────────────────┐
                                             │   Hardhat Local Node    │
                                             │   localhost:8545        │
                                             │   TemperatureLogger.sol │
                                             └──────────┬──────────────┘
                                                        │  SSE events
                                                        ▼
                                             ┌─────────────────────────┐
                                             │   Live Dashboard        │
                                             │   localhost:3000/       │
                                             └─────────────────────────┘

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🚀 Demo Setup (3 terminals)

Terminal 1 — Start Hardhat node

cd Blockchain
npx hardhat node

Keep this running. Copy any of the printed account private keys if needed.

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Terminal 2 — Deploy contract (once)

cd Blockchain
npm run deploy

This deploys TemperatureLogger.sol and writes deploy-info.json.

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Terminal 3 — Start relay server + dashboard

cd Blockchain
npm run relay

Open http://localhost:3000 in a browser to see the dashboard.

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🥧 Pico W Setup

1. Open IOT/pico_uploader.py and edit these lines:

   SSID     = "YOUR_WIFI_SSID"
   PASSWORD = "YOUR_WIFI_PASSWORD"
   RELAY_URL = "http://192.168.1.XXX:3000/reading"  # your PC's IP

   Find your PC's IP: run ipconfig in PowerShell, look for IPv4 Address

2. Flash pico_uploader.py to the Pico W using Thonny or mpremote:

   mpremote connect COM3 cp IOT/pico_uploader.py :main.py

3. The Pico W will:

   • Connect to WiFi (LED blinks slowly)
   • Read temp every 10 seconds
   • POST to relay → relay calls contract → dashboard updates live

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🎮 Demo without Physical Pico W

Click "▶ Simulate Pico W" on the dashboard to generate synthetic readings every 5 seconds — perfect for presenting without the hardware.

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📂 File Structure

Blockchain/
├── contracts/
│   └── TemperatureLogger.sol   ← Smart contract
├── ignition/modules/
│   └── deploy.js               ← Deployment + device auth script
├── relay/
│   ├── server.js               ← Relay server (Express + ethers.js)
│   └── public/
│       └── index.html          ← Live dashboard
├── hardhat.config.js
├── package.json
└── deploy-info.json            ← Generated after `npm run deploy`

IOT/
├── lm35_temperature.py         ← Standalone sensor test script
└── pico_uploader.py            ← Blockchain-connected uploader

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Smart Contract

TemperatureLogger.sol stores readings with:

• timestamp — block timestamp
• temperatureC — temperature × 100 (preserves 2 decimal places)
• deviceId — which device sent it

Only authorized devices can write. The deploy script pre-authorizes pico-w-001.

Key functions:

Function	Description
recordTemperature(int256, string)	Write a reading on-chain
getAllReadings()	Fetch all readings
getLatestReading()	Fetch the most recent
authorizeDevice(string)	Owner: add a device

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Dashboard Features

Feature	Description
🌡️ Live thermometer	Visual gauge that fills based on temperature
📈 Chart	Rolling 30-point temperature history
⛓️ Chain visualizer	Each reading shown as a block in the chain
📡 TX feed	Live transaction log with block numbers
🔔 Toast notifications	Pop-up on every new on-chain reading
🎮 Simulator	Generates readings without physical hardware