DIY CO2 meter and grapher for home and office use

Features

• display current CO2 level, temperature and humidity
• display historical graph of CO2 level for last 30 minutes
• switch to large display of CO2 level
• alarm when CO2 exceeds limit of 1000 ppm
• self calibration with countdown display

Components

• Arduino nano
• 0.96" OLED display
• MQ135 sensor
• DHT11 sensor
• 6x6x4.3mm button
• 3D printed case
• Screws

Schematics

Common VCC - arduino 5v pin, common GND - arduino GND pin.

Display connection: SDA to A4 pin, SCK to A5 pin, VDD to 3v3 pin, GND to common GND.

MQ135 connection: A0 to A0 pin, VCC to common VCC pin, GND to common GND pin.

DHT11 connection: OUT to D2 pin, "+" to common VCC pin, "-" to common GND pin.

Button: connection: to D2 pin and GND pin.

Assembly

See instructions at my website in Russian or translated to English.