Add Smart Irrigation System project: Arduino sketch, IoT upgrade, docs, and circuit reference

[Copilot]

Bootstraps a complete Smart Irrigation System project from a stub README — structured code, hardware docs, and an optional ESP8266 Wi-Fi upgrade.

Core Arduino sketch (code/smart_irrigation.ino)

• Reads soil moisture via analog A0; maps raw ADC (0–1023) to moisture %
• Controls pump relay on D7 using configurable MOISTURE_THRESHOLD (default 600) and RELAY_ACTIVE_LOW flag
• Non-blocking timed reads via millis() — no delay() in main loop
• Serial Monitor output at 9600 baud with raw value, %, and pump state

if (rawValue > MOISTURE_THRESHOLD) {
  setPump(true);   // soil dry — water
} else {
  setPump(false);  // moisture adequate — stop
}

IoT upgrade (code/esp8266_iot_upgrade.ino)

• NodeMCU ESP8266 variant with Wi-Fi + MQTT (PubSubClient)
• Publishes irrigation/moisture (int %) and irrigation/pump (ON/OFF) every 10 s
• Subscribes to irrigation/command — accepts ON, OFF, AUTO for remote override
• Auto-reconnects to both Wi-Fi and broker on dropout

Documentation (docs/)

• circuit_diagram.md — pin tables for sensor/relay/pump/LCD, ASCII schematic, power budget, safety notes (flyback diode, AC relay warning)
• components.md — full BOM with specs, costs ($24–$64), capacitive vs. resistive sensor trade-offs, sourcing options
• simulation_guide.md — step-by-step Tinkercad (free) and Proteus walkthroughs; troubleshooting table for common sim issues

images/README.md

Placeholder listing expected assets (Fritzing diagram, breadboard photo, serial monitor screenshot) with creation instructions.

Original prompt

Build a Smart Irrigation System using Arduino. Include Arduino code to read soil moisture sensor values and control a water pump via a relay module based on a threshold. Add proper comments in code, circuit diagram explanation, and documentation.

Create a structured project with folders for code, documentation, and images. Include a detailed README with setup instructions, components list, working principle, and future enhancements. Optionally add simulation support (Proteus/Tinkercad) and suggest IoT upgrade using ESP8266 for remote monitoring.