ESP32 Sensor Data Acquisition Board

ESP32 Sensor Data Acquisition Board

A custom two-layer PCB and Arduino firmware project for collecting ambient-light, temperature, humidity, and pressure data with an ESP32-C3.

Project status: Rev A was hand-assembled, programmed, and hardware-validated on 2026-08-22. The ESP32-C3 streams serial CSV data, the BME280 is detected over I2C, and the MCP6002-buffered light channel responds from covered to bright-light conditions. Long-duration logging and calibrated light measurement have not been completed.

Overview

This project combines a custom KiCad carrier board with an ESP32-C3 DevKitM-1. A photoresistor signal is conditioned by an MCP6002 op-amp and sampled by the ESP32 ADC, while a BME280 breakout provides environmental data over I2C. Six labeled test points expose the primary power and signal nets for structured bring-up and debugging.

flowchart LR
    LDR["Photoresistor divider"] --> OP["MCP6002 buffer"]
    OP --> ADC["ESP32-C3 GPIO0 / ADC"]
    BME["BME280 temperature, humidity, pressure"] -->|"I2C: GPIO4 SDA, GPIO5 SCL"| ESP["ESP32-C3"]
    ADC --> ESP
    ESP --> LED["Status LED on GPIO7"]
    ESP --> USB["CSV data over USB serial"]

Finished hardware

The Rev A PCB was assembled by hand with the ESP32-C3 in removable socket headers and the BME280 connected through the labeled J1 I2C header.

Key features

• ESP32-C3 DevKitM-1 controller on removable 1x15 sockets
• BME280 interface with 4.7 kOhm I2C pull-up resistors
• Photoresistor voltage divider buffered by an MCP6002 op-amp
• 100 nF local decoupling capacitor for the analog section
• Status LED with a 330 Ohm current-limiting resistor
• Six labeled test points: 3V3, GND, raw light signal, buffered ADC signal, SDA, and SCL
• CSV serial output suitable for logging or plotting
• Through-hole construction for accessible hand assembly and rework

Pin map

Firmware

The Arduino firmware:

1. Initializes the ESP32 ADC and the BME280 at address 0x77, then tries 0x76 as a fallback.
2. Samples the buffered light-sensor signal once per second.
3. Reads temperature, humidity, and pressure when the BME280 is available.
4. Emits one CSV row per second at 115200 baud.

Measured Rev A serial output:

BME280 detected
time_ms,light_raw,light_percent,temperature_C,humidity_percent,pressure_hPa
628,2058,50.3,25.70,47.22,1009.73

Build environment

• Arduino IDE 2.3.10
• esp32 board package by Espressif Systems 3.3.11
• Board target: ESP32C3 Dev Module
• Adafruit BME280 Library 2.3.0 and its installed dependencies

Rev A hardware validation

These captured values demonstrate end-to-end operation; they are not calibration data.

light_percent is the 12-bit ADC reading normalized to full scale; it is not a calibrated lux measurement. The light tests validate the complete photoresistor-divider, MCP6002-buffer, ADC, firmware, and serial-output path, but do not independently characterize the op-amp transfer function.

See VALIDATION.md for the full validation record and TEST_PLAN.md for the staged bring-up procedure.

Repository structure

.
├── fabrication/  Final Gerber and drill archive used for PCB ordering
├── firmware/     Arduino sketch folder and firmware source
├── hardware/     KiCad schematic, PCB, and project files
├── images/       KiCad renders and finished Rev A build photos
└── docs/         BOM, validation record, test plan, and resume notes

Design and validation status

• KiCad schematic ERC: 0 errors and 0 warnings
• KiCad PCB Editor DRC: 0 errors; one expected footprint/library mismatch warning after the ESP32 socket-pad customization
• Unrouted connections: 0
• Gerber and drill archive generated; PCB fabrication and delivery complete
• Rev A assembly, soldering, post-assembly short check, firmware upload, and serial output: complete
• BME280 I2C sensing and end-to-end light-channel response: hardware-validated

Optional follow-on characterization

• Run and archive a one-hour serial logging test
• Measure TP3 (RAW) and TP4 (ADC) simultaneously to quantify buffer tracking
• Calibrate the light channel against a lux reference if absolute illumination is required