Cellular HVAC Monitoring Device

Overview

Designed and deployed a cellular IoT monitoring device for commercial HVAC systems, owning hardware, firmware, cloud ingestion, analytics, and user-facing platforms end-to-end.

Problem

Commercial facilities lacked continuous, remote visibility into Direct Expansion (DX) HVAC performance. Diagnostics required on-site visits, manual measurements, and reactive maintenance, leading to inefficiency, downtime, and higher operational costs. Existing solutions were either too expensive, too complex to install, or insufficiently accurate for real-world HVAC diagnostics.

Constraints

• • Solo engineer responsible for the entire system
• • Large number of analog signals (15–16 per device)
• • Mixed-signal PCB design (analog + digital)
• • Field installation by technicians, not engineers
• • Cellular connectivity and power reliability
• • Production readiness and manufacturability
• • Tight timelines driven by enterprise customers

Solution

I designed a cellular HVAC monitoring device from scratch, covering the complete product lifecycle. This included an analog front-end supporting 4–20 mA pressure transducers, 10 kΩ thermistors, and 0–5 V CT/voltage sensors. I used an I²C-based ADC architecture with careful mixed-signal routing and designed the custom PCB in Eagle CAD.

The solution also involved purpose-built wire harnessing to simplify field installation and custom enclosure sourcing and modification. The device streams operational data to a cloud backend via a cellular data pipeline where it is processed, stored, and visualized in real time.

Architecture (High Level)

Sensors → Analog Front-End → MCU → Cellular Modem → AWS → TimescaleDB → Web Dashboard + Mobile App

My Responsibilities

• • Hardware architecture and schematic design
• • PCB layout (mixed-signal, multi-channel analog)
• • Enclosure design and mechanical integration
• • Firmware and device bring-up
• • Manufacturing coordination and field deployment support
• • AWS infrastructure design and operations
• • Backend APIs and data ingestion pipelines
• • Frontend dashboard architecture (with frontend engineer)
• • Mobile app architecture (Expo / React Native)

Impact

• • Thousands of devices deployed across enterprise customers
• • Enabled continuous HVAC performance monitoring and diagnostics
• • Reduced on-site service requirements
• • Contributed to ~$10M peak company valuation
• • Platform adopted by large commercial clients as a core monitoring tool

Confidentiality Note

Source code and schematics are not public due to IP and customer agreements.