ABOUT:

• We will use 2 different sensors. One Carbon Monoxide Sensor and one Ozone sensor. Both of them have the same pinout and identical circuitry associated with them. The Ozone sensor has a 100% cross sensitivity with Nitrogen Dioxide (NO2) and with Chlorine. It is therefore also used as a NO2 sensor.
• Both sensors are designed to measure gases in ambient air.
• These are high precision sensors and are rather expensive. However, if you'd like to rebuild our project at a later point, you can easily replace this sensor with a cheaper one.
• Gas levels are measured in PPM (parts per million). Different gases have differnt "threshold" / "danger" levels. See our "compounds" section for more information.
• The circuitry needed to use this sensor has been provided for you. If you'd like to rebuild it at a later point on your own, check out the sensor datasheets:
  Carbon Monoxide pdf and Ozone/Nitrogen Dioxide (pdf).

HOW IT WORKS:

• We won't discuss how this sensor works internally, for our purposes this depths of knowledge is not necessary. All we need to know is how to use the output pins. and how to use that information
  
  
  • Sensing: connected to analog pin
  • Counter: not connected (used internally)
  • Auxilary: connected to analog pin
  • Reference: not connected (used internally)
  
  
• The sensing pin generates a signal in response to atmospheric gases. By reading this signal into an analog pin, we convert this analog signal to a digital value. The sensing pin is sensitive to certain atmospheric conditions such as humidity and temperature, so we cannot fully rely on the signal value generated.
• The Auxilary pin is also affected by certain atmospheric conditions, but doesn't react to the atmospheric gases specified for this sensor (CO or O3/NO2).
• Hence we can simply substract the auxilary value from the sensing value and will optain the correct PPM information.
  
  
• Please note that the sensor is shipped with 2 grounding springs attached between the 4 output pins. Those springs should be reattached after each usage.
  
  

  look at this diagram before connecting the sensor to the Arduino

CO Sensor Performance Characteristics

(see datasheet for more info)

Ozone Sensor Performance Characteristics

(see datasheet for more info)

CO/O3 Sensor Circuit

(this circuit has been provided for you, see datasheet for more info)