Problem & Motivation

Long-term ecological sensing and sensor-driven art installations are often constrained by power, communications reliability, and timestamp integrity in outdoor deployments. Opuntia was built to demonstrate that a compact, solar-powered station can reliably collect, backfill, and serve environmental telemetry (temperature, humidity, pressure, soil moisture, UV) to a web dashboard for weeks without human intervention. This project was developed during an IoT course as a practical research prototype. :contentReference[oaicite:3]3

Approach & System Overview

Opuntia emphasizes robustness and autonomy rather than experimental novelty: hardware and software are designed around a strict power budget, reliable timekeeping, and outage recovery.

• Hardware: ESP32-C3 microcontroller, BME280 (temp/humidity/pressure), soil-moisture probe, UV sensor, solar charging circuit with Li-ion battery and BMS.
• Power strategy: Duty-cycle the MCU and radio (wake, read, transmit, sleep) to minimize energy use; use the RTC to preserve timestamps across deep sleep.
• Connectivity & backend: Wi-Fi to a local router; Node.js/Express API writing to MongoDB for time-series logging and an interactive React + D3 dashboard.

Key Technical Decisions

• Reliable timestamps are essential: the firmware compares RTC time vs. expected wake intervals and marks/backfills missing samples on reconnect to preserve continuity.
• Duty cycling and conservative sensor polling (hourly by default) balanced data fidelity and battery life; the power system was sized to survive multi-day cloudy periods.
• Backend uses a document store (MongoDB) to allow flexible, schema-light time-series logging and easy prototyping of front-end visualizations.

Evaluation & Results

• Field test (30 days): The station recorded hourly readings with no downtime; battery remained in safe operating range through cloudy intervals.
• Sensor accuracy: Compared to a lab reference, the BME280 readings were within acceptable error bounds (within about 5% for humidity/temperature in the test period).
• Web access: Dashboard successfully retrieved hourly updates and supported historical queries and visualization.

(High-level results summarized from project notes and course write-up.) :contentReference[oaicite:4]4

My Contribution

• Designed the power system and duty-cycling strategy for reliable off-grid operation.
• Wrote ESP32 firmware (Arduino/C++) to handle sensor reads, RTC-based wake/sleep, and robust transmission with reconnect/backfill logic.
• Built the backend API and the React/D3 dashboard for live and historical visualization.
• Led the field deployment and validation tests.

Outcomes & Next Steps

• Opuntia demonstrates practical autonomy for sensor-driven installations and ecological art. Next steps include adding OTA updates, encrypted telemetry, and optional cellular failover for remote deployments.