Building an I2C Environmental Sensor Module Tutorial

Overview

This tutorial covers designing a comprehensive environmental monitoring sensor module using tscircuit. You'll learn about I2C communication, multi-sensor integration, environmental sensing principles, and low-power design for battery-operated applications.

Project Specifications

Parameter	Value
Board Size	25mm × 35mm
Power Supply	3.3V regulated
Communication	I2C (SDA/SCL)
Sensors	BME280 + CCS811
Interface	Qwiic/Stemma QT compatible

Sensors Overview

BME280 (Bosch)

Measures temperature, humidity, and barometric pressure:

Parameter	Range	Accuracy
Temperature	-40°C to +85°C	±1°C
Humidity	0-100% RH	±3%
Pressure	300-1100 hPa	±1 hPa

CCS811 (AMS)

Measures carbon dioxide (CO2) and volatile organic compounds (VOCs):

Parameter	Range	Accuracy
eCO2	400-8192 ppm	±50 ppm
TVOC	0-1187 ppb	—

Components

Ref	Part	Description	Footprint
U1	BME280	Temp/Humidity/Pressure	`lga-8`
U2	CCS811	CO2/VOC Sensor	`mlga-10`
U3	AP2112-3.3	3.3V LDO regulator	`sot-23-5`
J1	Qwiic Connector	I2C + Power	`jst-ph-4pin`
J2	Optional Header	Breadboard pins	`pin_header_1x4`
C1	Input capacitor	10µF	`0805`
C2	Output capacitor	10µF	`0805`
R1	I2C pull-up	4.7kΩ	`0805`
R2	I2C pull-up	4.7kΩ	`0805`
LED1	Power LED	Blue	`0805`

Step 1: BME280 Sensor

The BME280 uses an I2C interface with selectable address (0x76 or 0x77):

<chip
  name="U1"
  footprint="lga-8"
  pcbX={0}
  pcbY={5}
/>

/* BME280 Pinout */
<trace from=".U1 .VDD" to="net.3V3" />
<trace from=".U1 .GND" to="net.GND" />
<trace from=".U1 .SDA" to="net.SDA" />
<trace from=".U1 .SCL" to="net.SCL" />
<trace from=".U1 .CSB" to="net.3V3" />  /* I2C mode */
<trace from=".U1 .SDO" to="net.GND" />  /* Address 0x76 */

BME280 Mounting Considerations

The BME280 should be mounted with the sensing element exposed to air:

Top side: Keep the port hole unobstructed
No conformal coating: Over the sensor
Isolation: Separate from heated components

Step 2: CCS811 Sensor

The CCS811 requires a burn-in period and periodic baseline resets:

<chip
  name="U2"
  footprint="mlga-10"
  pcbX={0}
  pcbY={-5}
/>

/* CCS811 Pinout */
<trace from=".U2 .VCC" to="net.3V3" />
<trace from=".U2 .GND" to="net.GND" />
<trace from=".U2 .SDA" to="net.SDA" />
<trace from=".U2 .SCL" to="net.SCL" />
<trace from=".U2 .WAK" to="net.GND" />  /* Wake pin low */
<trace from=".U2 .INT" to="net.INT" />
<trace from=".U2 .RST" to="net.3V3" />  /* Hardware reset */

CCS811 Environmental Considerations

The CCS811 is sensitive to:

Temperature changes: Allow 20 minutes warm-up
High humidity: Can affect readings temporarily
Airflow: Needs fresh air for accurate VOC measurements

Step 3: I2C Bus Design

Address Configuration

/* BME280: SDO grounded = 0x76 */
/* CCS811: Addr pin = low = 0x5A */

<resistor name="R1" footprint="0805" resistance="4k7" pcbX={15} pcbY={0} />
<resistor name="R2" footprint="0805" resistance="4k7" pcbX={15} pcbY={3} />

<trace from="net.3V3" to=".R1 .pos" />
<trace from="net.3V3" to=".R2 .pos" />
<trace from=".R1 .neg" to="net.SDA" />
<trace from=".R2 .neg" to="net.SCL" />

I2C Pull-Up Resistor Selection

Bus Speed	Min R (mA)	Max R (kΩ)
100kHz	1kΩ	10kΩ
400kHz	2kΩ	4kΩ
1MHz	1kΩ	2kΩ

We use 4.7kΩ for standard 100kHz operation with 2 sensors.

Step 4: Qwiic/Stemma QT Connector

<chip name="J1" footprint="jst-ph-4pin" pcbX={20} pcbY={0} />

/* Qwiic pinout: 1=GND, 2=3V3, 3=SDA, 4=SCL */
<trace from=".J1 .1" to="net.GND" />
<trace from=".J1 .2" to="net.3V3" />
<trace from=".J1 .3" to="net.SDA" />
<trace from=".J1 .4" to="net.SCL" />

Step 5: Power Supply

<chip name="U3" footprint="sot-23-5" pcbX={-15} pcbY={0} />

<capacitor name="C_IN" footprint="0805" capacitance="10µF" pcbX={-17} pcbY={2} />
<capacitor name="C_OUT" footprint="0805" capacitance="10µF" pcbX={-13} pcbY={2} />

<trace from=".U3 .VIN" to="net.VIN" />
<trace from=".U3 .GND" to="net.GND" />
<trace from=".U3 .VOUT" to="net.3V3" />

<trace from="net.VIN" to=".C_IN .pos" />
<trace from="net.GND" to=".C_IN .neg" />
<trace from="net.3V3" to=".C_OUT .pos" />
<trace from="net.GND" to=".C_OUT .neg" />

Step 6: Power LED

<led name="LED1" color="blue" footprint="0805" pcbX={-20} pcbY={8} />
<resistor name="R_LED" footprint="0805" resistance="4k7" pcbX={-22} pcbY={8} />

<trace from="net.3V3" to=".R_LED .pos" />
<trace from=".R_LED .neg" to=".LED1 .pos" />
<trace from=".LED1 .neg" to="net.GND" />

Complete Circuit

export default () => {
  return (
    <board width="35mm" height="25mm">
      {/* BME280 - Temp/Humidity/Pressure */}
      <chip name="U1" footprint="lga-8" pcbX={0} pcbY={5} />
      
      {/* CCS811 - CO2/VOC */}
      <chip name="U2" footprint="mlga-10" pcbX={0} pcbY={-5} />
      
      {/* 3.3V LDO */}
      <chip name="U3" footprint="sot-23-5" pcbX={-15} pcbY={0} />
      
      {/* Qwiic Connector */}
      <chip name="J1" footprint="jst-ph-4pin" pcbX={20} pcbY={0} />
      
      {/* Power LED */}
      <led name="LED1" color="blue" footprint="0805" pcbX={-20} pcbY={8} />
      <resistor name="R_LED" footprint="0805" resistance="4k7" pcbX={-22} pcbY={8} />
      
      {/* Bypass Capacitors */}
      <capacitor name="C_IN" footprint="0805" capacitance="10µF" pcbX={-17} pcbY={2} />
      <capacitor name="C_OUT" footprint="0805" capacitance="10µF" pcbX={-13} pcbY={2} />
    </board>
  )
}

Arduino Code Example

#include <Wire.h>
#include <Adafruit_BME280.h>
#include "CCS811.h"

Adafruit_BME280 bme;
CCS811 ccs811;

void setup() {
  Serial.begin(115200);
  Wire.begin();
  
  // Initialize BME280
  if (!bme.begin(0x76)) {
    Serial.println("BME280 not found!");
  }
  
  // Initialize CCS811
  ccs811.begin();
}

void loop() {
  // Read BME280
  float temp = bme.readTemperature();
  float hum = bme.readHumidity();
  float pres = bme.readPressure() / 100.0F;
  
  // Read CCS811
  ccs811.readData();
  int co2 = ccs811.geteCO2();
  int tvoc = ccs811.getTVOC();
  
  Serial.print("Temp: "); Serial.print(temp, 1); Serial.println(" C");
  Serial.print("Humidity: "); Serial.print(hum, 1); Serial.println(" %");
  Serial.print("Pressure: "); Serial.print(pres, 1); Serial.println(" hPa");
  Serial.print("CO2: "); Serial.print(co2); Serial.println(" ppm");
  Serial.print("TVOC: "); Serial.print(tvoc); Serial.println(" ppb");
  
  delay(1000);
}

Python (Raspberry Pi) Example

import smbus2
import bme280
import ccs811
import time

bus = smbus2.SMBus(1)

# Initialize BME280
calibration_params = bme280.load_calibration_params(bus, 0x76)

# Initialize CCS811
sensor = ccs811.CCS811(bus, 0x5a)
time.sleep(1)  # Wait for sensor to warm up

while True:
    # Read BME280
    data = bme280.read(bus, 0x76, calibration_params)
    print(f"Temp: {data.temperature:.1f} C")
    print(f"Humidity: {data.humidity:.1f} %")
    print(f"Pressure: {data.pressure:.1f} hPa")
    
    # Read CCS811
    if sensor.data_ready:
        print(f"CO2: {sensor.co2} ppm")
        print(f"TVOC: {sensor.tvoc} ppb")
    
    time.sleep(1)

Enclosure Design

Ventilation Requirements

Sensor area: Include ventilation holes near sensors
Size: Minimum 2mm diameter holes
Pattern: Staggered pattern to prevent dust ingress
Location: Bottom of enclosure for convection

Material Considerations

Avoid: ABS plastic can outgas VOCs
Preferred: Acrylic, aluminum, or ABS with outgassing period
Sealing: Use silicone gaskets for weatherproofing

PCB Layout Guidelines

Sensor Placement

Keep sensors away from heat sources: MCU, voltage regulator
Consider airflow: Position sensors in natural airflow path
Separation: Keep BME280 and CCS811 at least 5mm apart

Power Design

Low noise: CCS811 is sensitive to supply noise
Decoupling: Use ceramic capacitors near each sensor
Ground plane: Solid ground under sensor area

Cost Estimate

Component	Unit Cost	Qty	Total
BME280	$2.50	1	$2.50
CCS811	$3.00	1	$3.00
AP2112-3.3	$0.25	1	$0.25
Qwiic connector	$0.30	1	$0.30
Passives	$0.05	5	$0.25
PCB (2-layer)	$0.50	1	$0.50
Total			$6.80

Summary

You've designed a complete environmental sensor module covering:

I2C communication with multiple sensors
BME280 temperature, humidity, and pressure sensing
CCS811 CO2 and VOC detection
Qwiic/Stemma QT compatibility
Power supply design with filtering
Arduino and Python code examples
Enclosure design for sensor accuracy

This module is ready for integration into environmental monitoring projects, smart home systems, or air quality monitoring applications.

Overview​

Project Specifications​

Sensors Overview​

BME280 (Bosch)​

CCS811 (AMS)​

Components​

Step 1: BME280 Sensor​

BME280 Mounting Considerations​

Step 2: CCS811 Sensor​

CCS811 Environmental Considerations​

Step 3: I2C Bus Design​

Address Configuration​

I2C Pull-Up Resistor Selection​

Step 4: Qwiic/Stemma QT Connector​

Step 5: Power Supply​

Step 6: Power LED​

Complete Circuit​

Arduino Code Example​

Python (Raspberry Pi) Example​

Enclosure Design​

Ventilation Requirements​

Material Considerations​

PCB Layout Guidelines​

Sensor Placement​

Power Design​

Cost Estimate​

Summary​