PCB Final

🔥 Fire Alarm — Temperature Sensor Alarm System

CMPE2700 — PCB Design Project STM32G0B1RETx · DS18B20 · DFRobot Gravity 7-Segment Displays · USB-C Powered

Overview

A temperature monitoring and alarm system built on a custom PCB. The DS18B20 sensor continuously reads ambient temperature and displays it on a 4-digit 7-segment display. When the temperature exceeds a configurable threshold, an alarm LED activates. The alarm must be manually acknowledged by pressing the onboard button.

A second 7-segment display shows the current alarm threshold for reference at all times.

Hardware

How It Works

1. The DS18B20 reads temperature every second over the 1-Wire bus
2. The current temperature is shown on Display 1 (I2C1)
3. The alarm threshold is shown on Display 2 (I2C2)
4. If the temperature exceeds the threshold, the alarm LED turns on
5. Press the onboard button to acknowledge and clear the alarm

PCB

📷 PCB photo — upload a JPG/PNG version of the image to add it here

Known Hardware Issue — J1 / J2 Header Pin Swap

⚠️ Workaround required — jumper wires needed

The I2C headers J1 and J2 were routed with the following pinout:

PCB Header (J1/J2):   5V · GND · SDA · SCL

However, the mating female connectors on the DFRobot Gravity displays use:

Display Connector:    5V · GND · SCL · SDA

The SDA and SCL lines are swapped between the PCB header and the display connector. As a result, the displays cannot be plugged in directly — they will not communicate.

Fix: Use jumper wires to cross SDA and SCL between the header and the display connector before plugging in.

This will be corrected in the next PCB revision by swapping the SDA/SCL positions on J1 and J2 in the schematic.

Firmware

The firmware is written in C using the STM32 HAL library and structured across three STM32CubeIDE projects:

Firmware Repository Structure

Firmware/
├── Temperature sensor/         # DS18B20 test project
├── SevenSeg/                   # 7-segment display test project
└── Temperature alert system/   # Final alarm application
Hardware/
├── PCB_Final.kicad_pcb         # PCB layout
├── PCB_Final.kicad_sch         # Schematic
└── PCB_Final.kicad_pro         # KiCad project file

Programming the STM32

1. Connect an ST-Link programmer to the SWD header on the PCB
2. Power the board via USB-C
3. Open the project in STM32CubeIDE
4. Build and flash using Run → Debug or Run → Run

Pin Assignments

Author

Aldrich Dias — CMPE2750, 2026