1. The Z19C carbon dioxide gas sensor (hereinafter referred to as the "sensor") is a type of 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. 2. It has a built - in temperature compensation function, and is equipped with both serial output and PWM output, which makes it convenient to use. This sensor is made by combining the mature infrared absorption gas detection technology with precise optical path design and circuit design. 3. Detected gas: Carbon dioxide 4. Supply voltage: DC (5.0 ± 0.1) V 5. Average current: Less than 40mA (@5V power supply) 6. Current: 125 to (the original information here is incomplete) (@5V power supply) 7. Interface level: 3.3V (compatible with 5V) 8. Measurement range: 400 - 5000PPM 9. Warm - up time: 1 minute 10. Response time: T90 is less than 120 seconds 11. Operating temperature: - 10 - 50°C 12. Operating humidity: 0 - 95%RH (no condensation) 13. 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 14. Type: Gas sensor 15. Model: Z19C 16. Color: Golden 17. Material: Plastic 18. Dimensions: 33 x 20mm 19. Package contents: 1 Z19C infrared CO₂ sensor module with cable 20. Only the above - mentioned package contents are included, and other items are not included. 21. Note: Light and different displays may cause the color of the item in the picture to be slightly different from the actual one. A measurement error of ±1 - 3cm is allowed.