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Tutorials

Building an I2C Environmental Sensor Module

Overview​

This tutorial builds a compact BME280 environmental sensor module. The board exposes power, ground, SDA, and SCL on a header, includes pull-up resistors for the I2C bus, and adds an optional connector for a small I2C OLED display.

Requirements​

  • BME280 sensor for temperature, humidity, and pressure.
  • 4-pin host header with GND, VCC, SDA, and SCL.
  • 4.7 kΩ pull-up resistors on SDA and SCL.
  • 100 nF decoupling capacitor near the sensor.
  • Optional OLED header on the same I2C bus.

I2C pull-up explanation​

I2C devices pull the bus low but do not actively drive it high. Pull-up resistors return SDA and SCL to VCC when the bus is idle. For a short 3.3 V sensor module, 4.7 kΩ is a practical default.

Step 1: Add the sensor​

export default () => (
  <board width="35mm" height="25mm">
    <chip name="U1" footprint="qfn8" manufacturerPartNumber="BME280" pcbX={0} pcbY={0} />
  </board>
)

Step 2: Add the host header and pull-ups​

<chip name="J1" footprint="pinrow4" manufacturerPartNumber="I2C host header" pcbX={-12} pcbY={0} />
<resistor name="R1" resistance="4.7k" footprint="0402" pcbX={8} pcbY={5} />
<resistor name="R2" resistance="4.7k" footprint="0402" pcbX={8} pcbY={-5} />

Step 3: Add optional OLED expansion​

<chip name="J2" footprint="pinrow4" manufacturerPartNumber="Optional I2C OLED header" pcbX={12} pcbY={0} />

Complete example​

export default () => (
  <board width="35mm" height="25mm">
    <chip name="U1" footprint="qfn8" manufacturerPartNumber="BME280" pcbX={0} pcbY={0} />
    <chip name="J1" footprint="pinrow4" manufacturerPartNumber="I2C host header" pcbX={-12} pcbY={0} />
    <chip name="J2" footprint="pinrow4" manufacturerPartNumber="Optional I2C OLED header" pcbX={12} pcbY={0} />
    <resistor name="R1" resistance="4.7k" footprint="0402" pcbX={8} pcbY={5} />
    <resistor name="R2" resistance="4.7k" footprint="0402" pcbX={8} pcbY={-5} />
    <capacitor name="C1" capacitance="100nF" footprint="0402" pcbX={0} pcbY={7} />
    <trace from=".J1 > .pin2" to=".U1 > .pin8" />
    <trace from=".J1 > .pin1" to=".U1 > .pin1" />
    <trace from=".J1 > .pin3" to=".U1 > .pin3" />
    <trace from=".J1 > .pin4" to=".U1 > .pin4" />
  </board>
)

Layout and bring-up checklist​

  • Place the BME280 away from regulators and other heat sources.
  • Keep the decoupling capacitor close to the sensor power pins.
  • Label GND, VCC, SDA, and SCL on both headers.
  • Scan the I2C bus after assembly and confirm the expected BME280 address.
  • Compare sensor readings against a known reference during first test.