🌡️ Environment Sensor Node

A low-power environmental sensor node built on Arduino Mini Pro that measures ambient conditions and transmits readings over LoRa.

📋 Table of Contents

• Overview
• Hardware
• Pinout
• LoRa Configuration
• Message Protocol
• Power Management
• Building & Flashing
• Debug Mode
• Receiver
• Schematic
• License

Overview

This project implements an ultra-low power environmental monitoring node capable of:

• Measuring atmospheric pressure (BMP180)
• Measuring temperature and humidity (DHT22)
• Monitoring battery voltage
• Transmitting all readings via LoRa radio (868 MHz band)

The node is designed to run for months on two AA batteries thanks to aggressive power management strategies.

Hardware

Component	Purpose	Interface
Arduino Mini Pro (3.3V/8MHz)	Main microcontroller	ATmega328P
BMP180	Barometric pressure & temperature	I2C
DHT22 (AM2302)	Temperature & humidity	Digital
HopeRF RFM95W	LoRa wireless transmission	SPI
LED	Status/error indication	GPIO
Voltage divider	Battery monitoring	ADC

Pinout

Arduino Pin	Function	Notes
Pin 3	Battery voltage measurement	ADC with internal 1.1V reference
Pin 4	Power control	Enables voltage measurement circuit
Pin 5	DHT22 data	Sensor communication
Pin 6	DHT22 power	On-demand power switching
Pin 7	BMP180 power	On-demand power switching
Pin 8	Status LED	Error indication & activity
SDA/SCL	I2C bus	BMP180 communication
SPI pins	RFM95W communication	MOSI, MISO, SCK, SS

LoRa Configuration

Parameter	Value
Frequency	868.45 MHz
Bandwidth	500 kHz
Spreading Factor	128
Coding Rate	4/5
TX Power	+5 dBm
Preamble Length	8 symbols
Address (FROM)	0x0A
Address (TO)	0x0B

Message Protocol

Each transmission sends a 16-byte packet containing:

struct Message {
    int32_t pressure;    // Pascals (from BMP180)
    int32_t humidity;    // Percent × 10 (from DHT22)
    int32_t temperature; // Celsius × 10 (from DHT22)
    int32_t voltage;     // Millivolts (battery)
};

Packets include an incrementing packet_id for sequencing and use RadioHead's addressing scheme.

Power Management

• Sleep current: <10 μA
• Measurement interval: ~112 seconds (14 × 8-second sleep cycles)
• Strategies:
  • Sensors powered on-demand via GPIO
  • I2C pull-ups disabled when BMP180 is off
  • MCU uses LowPower.powerDown() during all wait periods
  • DHT22 library modified to use sleep instead of delays
  • Radio put to sleep immediately after transmission

Building & Flashing

Prerequisites

1. Arduino IDE (1.x or 2.x)
2. Required libraries:
   • LowPower (Rocket Scream)
   • Adafruit BMP085
   • RadioHead (RH_RF95)
3. ISP programmer (e.g., USBasp)

Steps

1. Open firmware/environment-sensor-node.ino in Arduino IDE
2. Select board: Arduino Pro or Pro Mini
   • Processor: ATmega328P (3.3V, 8 MHz)
3. Connect ISP programmer
4. Upload via Upload using Programmer

Debug Mode

Uncomment #define DEBUG 1 at the top of the sketch to enable serial output at 57600 baud.

⚠️ Keep debug disabled in production to minimize power consumption.

Receiver

Pair with the Raspberry Pi-based LoRa gateway: 👉 RFM95-MQTT-Gateway

Schematic

License

MIT License — see LICENSE for details.

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Built for long-term environmental monitoring with minimal maintenance.