The sensor can be purchased in 3 ranges: a range of 2000 ppm, 5000 ppm and 10000 ppm. This sensor is available in many Chinese online websites. MH-Z14A price varies, but you can get it for approximately $18 in most Websites.
My personal favrate for this product is Aliexpress Low Price + Wolrdwide Delivery
MH-Z14A is an Infrared Carbon Dioxide Sensor for accurate NDIR (nondispersive infrared) Co2 measurement using Arduino, STM32, Raspberry Pi. This NDIR Co2 sensor is a small size, common type sensor, NDIR principle to sense the presence of CO2 gas in the air. This NDIR Co2 sensor provides good selectivity, long life and non-oxygen dependent.
This MH-Z14A NDIR Co2 sensor module comes with built-in temperature compensation. MH-Z14A is a most advanced CO2 sensor that transmits a calibrated output valuein following format,
Digital output, [Serial Port (UART, TTL level)]
Analog Voltage output, (0.4 – 2V)
This Infrared Carbon Dioxide Sensor makes it easy to measure atmospheric Co2 percentage measurement posible using Arduino code. MH-Z14A is an infrared gas sensor is developed by the deep integration of infrared absorbing gas sensing technology with the precision optical circuit.
Due to the limited resolution of the analog ports (only 1023 values between 0 and 5 volts), the analog output of the sensor (0 to 2.4 V) is not very usable.
The digital output communicates via PWM or UART. The signal (off and for UART also on) runs at 3.3 volts. This means that you have to change your reference signal on your Arduino to 3.3 volts – or you have to increase the signal to 5 volts by hardware.