A. The Z19C carbon dioxide gas sensor (hereinafter referred to as the "sensor") is a general - purpose smart small - sized sensor. It uses the non - dispersive infrared (NDIR) principle to detect the presence of carbon dioxide (CO₂) in the air. B. It has a built - in temperature compensation function, and is equipped with both serial output and PWM output, which is convenient for use. This sensor is made by closely combining the infrared absorption gas detection technology with optical path design and circuit design. C. Detected gas: Carbon dioxide D. Supply voltage: DC (5.0 ± 0.1) V E. Average current: Less than 40mA (@5V power supply) F. Current: 125 to (the original information here is incomplete) (@5V power supply) G. Interface level: 3.3V (compatible with 5V) H. Measurement range: 400 - 5000PPM I. Warm - up time: 1 minute J. Response time: T90 is less than 120 seconds K. Operating temperature: - 10 - 50°C L. Operating humidity: 0 - 95%RH (no condensation) M. Pin definitions: - Vin: Power supply + (input) - GND: Power supply - (ground) - PWM: PWM - Hd: HD (calibration, low - level for more than 7 seconds is valid) - Rx: UART (RXD) TTL level data input - Tx: UART (TXD) TTL level data output N. Type: Gas sensor O. Model: Z19C P. Color: Golden Q. Material: Plastic R. Dimensions: 33 x 20mm S. Package contents: 1 Z19C infrared CO₂ sensor module with cable T. Only the above - mentioned package contents are included, and other items are not included. U. Note: Light and different displays may cause the color of the item in the picture to be slightly different from the actual one. The measurement error is allowed to be ±1 - 3cm.