Institution: Dedan Kimathi Center for Energy Studies
Hardware Revision: Rev 001 (Production Release)
The Heat Pump Monitoring System is a custom-designed, industrial-grade IoT hardware architecture built to capture, process, and transmit high-precision thermodynamic data. The primary objective of this system is to continuously calculate the real-time efficiency (Coefficient of Performance - COP) of a hydronic heat pump.
By offloading complex floating-point mathematics and high-speed hardware interrupts to a dedicated Cortex-M4 microcontroller, and bridging it with an ESP32 Network Co-Processor for Wi-Fi telemetry, this project ensures research-grade data integrity and robust operational stability.
The system employs a dual-microcontroller topology to separate strict real-time data acquisition from high-latency network tasks.
- The Core Engine (Data Acquisition): An STM32F411CEU6 handles all hardware-level sensor polling, microsecond-precise 1-Wire communication, and interrupt-driven frequency counting.
- The Network Co-Processor (Telemetry): An ESP32-WROOM-32E is bridged to the STM32 via a high-speed UART interface. The STM32 streams formatted data payloads to the ESP32, which securely publishes the metrics to a cloud dashboard via MQTT over Wi-Fi.
- STM32F411CEU6 (100 MHz ARM Cortex-M4): Selected for its integrated Floating-Point Unit (FPU), which is critical for calculating fluid flow rates and thermodynamic formulas without processor latency.
- Air Quality (SHT31): Dual high-precision digital I2C sensors monitor the Air-In and Air-Out temperatures (±0.2°C) and humidity. Utilizing distinct hardware addresses (
0x44and0x45), both sensors efficiently share a single I2C bus (MCU_SCL/MCU_SDA). - Fluid Temperature (DS18B20): Waterproof stainless-steel probes track the H2O-In and H2O-Out lines. Leveraging their unique 64-bit laser-etched ROM IDs, multiple probes are parallel-wired onto a single 1-Wire data pin (
PB12), simplifying the PCB routing. - Hydronic Flow Rate (YF-S201): An inline 5V Hall Effect flow meter generates digital square waves based on fluid velocity. The STM32 reads these pulses via an External Interrupt (
PA1) to calculate real-time Liters per Minute (L/min). - Local Display: A 5V 16x2/20x4 I2C LCD Backpack provides real-time, on-site diagnostics.
The physical Printed Circuit Board (PCB) was designed with strict Design for Manufacturing (DFM) principles and robust electrical protection.
- Mixed-Voltage Signal Translation: To safely interface the 3.3V STM32 with the 5V LCD Display, a PCA9306 dedicated bidirectional logic level translator IC is utilized to ensure high-speed I2C data integrity.
- Overvoltage Clamping: The 5V square wave from the YF-S201 flow sensor is safely clamped before reaching the STM32 using a 4.7kΩ pull-up resistor and a BAT54W Schottky diode, safely shunting overvoltage spikes to the 3.3V rail.
- ESD & Power Protection: The USB-C input utilizes a USBLC6-2SC6 transient voltage suppression array for ESD protection on the data lines. Mandatory 5.1kΩ pull-down resistors on CC1/CC2 ensure correct 5V power negotiation from smart USB-C hosts.
- DFM & Factory Assembly: The PCB layout features four optical fiducial markers for automated SMT Pick-and-Place alignment, alongside standard mechanical mounting holes for enclosure installation.
This project successfully delivered a custom, production-ready IoT hardware architecture capable of capturing robust, research-grade thermodynamic data for real-time heat pump analysis. By combining advanced logic-level translation, intelligent communication bus merging, and distinct separation of networking and real-time processing duties, the board serves as a highly scalable platform for energy efficiency studies.
