The MH-Z19C carbon dioxide gas sensor (hereinafter referred to as the sensor) is a general-purpose intelligent small sensor that uses the principle of non-dispersive infrared (NDIR) to detect the presence of C02 in the air. Built-in temperature compensation: simultaneously has serial output, PWM output, easy to use. The sensor is a high-performance sensor made by closely combining mature infrared absorption gas detection technology with sophisticated optical circuit design and sophisticated circuit design. Detection gas:carbon dioxide Power supply voltage:DC (5.0±0.1) V Average current:Less than 40mA (@5V power supply) current:125 to (@5V power supply) Interface level:3.3v(compatible with 5v) Measuring range:400-5000PPM optional Output signal:serial UART(TL level 3.3V) Warm-up time:1min Response time:T90 Less than 120s Working temperature:-10-50℃ Working humidity:0-95%RH(no condensation) Pin description: Vin:Power +(in) GND:power supply-(GND) PWM:PWM Hd:HD (zero calibration, low level is effective for more than 7 seconds) Rx:UART (RXD) TTL level data input Tx:UART (TXD) TTL level data output Output method: PWM output Assume the measurement range is 400-2000ppm CO2:Concentration output range: 400-2000ppm Period:1004ms±5% High level output at the beginning of the cycle: 2ms (theoretical value) Central period:1000ms±5% Low level output at the end of the period: 2ms (theoretical value) Calculation formula for obtaining current CO2 concentration value by PWM: Cppm=2000X (TH-2ms)/(TH+TL-4ms) Cppm: CO2 concentration value calculated by the unit of ppm TH: the time when the output is high level in one output cycle TL: the time when the output is low in one output cycle Due to different product batches, the appear