Air Pollution Detector




This device is intended to provide the user with a cost-efficient means of determining air quality. Our sensor focuses on the five components of the Environmental Protection Agency’s Air Quality Index: ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrous oxide. This device detects all of these pollutants except sulfur dioxide. The device also includes a town gas sensor to alert the user to gas leaks or the presence of flammable gases. Furthermore, a temperature and humidity sensor is included as these conditions can impact the performance of the gas sensors.

We have yet to fully calibrate our device, but we have extracted data from sensor data sheets to make some preliminary estimations. The sensors used are relatively inexpensive and vary greatly from component to component so they need to be calibrated with known concentrations of the target gasses. We have not yet had the opportunity do so.

Air Pollution Detector

Step 1: Materials

Control and Power

  • Arduino Uno
  • 5V power supply
  • RGB 16×2 LCD shield

Sensors

  • Shinyei PPD42 Particulate Matter Detector
  • MQ-2 Gas Sensor
  • MQ-9 Gas Sensor
  • MiCS-2714 Gas Sensor (NO2)
  • MiSC-2614 Gas Sensor (Ozone)
  • Keyes DHT11 Temperature and Humidity Sensor

Box and Assembly

  • Access to 3D printer
  • Solder Board
  • 5V fan
  • 10 to 15 wires of gauge 24

Step 2: Overall Circuit Diagram

The circuit diagram above is the entirety of this pollution detector works. A detailed circuit diagram for the solder board follows later. Note that you can change most of the digital ports and analog ports that sensors enter should you need to do so (for any reason); this will only require that you edit the code we have provided to account for these changes.

Step 3: Particulate Matter Sensor

We use two Shinyei PPD42 Dust Sensors to collect data about particulate matter.

Each Shinyei Detector has two signal outputs: one for small particulate matter (left yellow wire in the picture above) and one for larger particulate matter. These output signals are connected the digital inputs of the Ardiuno. The detector needs to be powered by supplying +5V and ground to the ports on the detector. See the overall circuit diagram for details.

Each detector uses an infrared LED and a photodetector to measure scattering off of small airborne particulates. Internal circuitry turns the photodetector output into digital output signals. Generally the sensor outputs a +5V signal, when it detects particles is sends out a low-voltage pulse. The fraction of the time that the output signal is low or the “low-pulse occupancy percentage” is proportional to the concentration of particulate matter in the air.

A detailed reverse engineering analysis of the Shinyei PPD42 by Tracy Allen can be found at http://takingspace.org/wp-content/uploads/ShinyeiP…

Step 4: Gas Sensor Circuit Board

Above is the circuit diagram for the circuit board hosting the gas sensors and temperature/humidity sensor. Details about mounting each of the separate devices are in the following steps. Note that your circuit board can look different from ours physically. In fact, we recommend you print a circuit board for the surface mount devices instead of using a solder board. It should work just as well as long as you follow the circuit diagram.

Step 5: Ozone and NO2 sensors

We use surface-mount sensors MiCS-2614 and MiCS-2714 to detect Ozone and Nitrogen Dioxide respectively.

Both of these devises use an internal resistor as their sensing element. The sensing resistor is connected between the pins (G) and (K) in the diagram above. Use an ohmmeter to check that you have found the right pins. The resistance should be on the order of 10-20 kΩ.

Both devices also have a heating element between pins (A) and (H). This heating element keeps the sensing element at the appropriate temperature. The resistance of the heating element is 50-60Ω.

Ideally these devices should be surface mounted onto a circuit board. However, in the absence of a circuit board printer it is still possible to carefully solder to the back of these devices using very low temperature solder and much care.

As shown in the solder board circuit diagram, we place the 82Ω resistor and the 131Ω resistor in series with the heating elements of the MiCS-2614 and MiCS-2714 units respectively. This ensure that the heating elements receive the proper level of power. If you don’t have access to a 131Ω resistor (it is not a standard value) use a 120Ω resistor and a 12Ω resistor in series.

We place the sensing resistors in both devises in series with 22kΩ resistors to create a voltage divider. From the voltage at the output of the voltage divider we can calculate the sensing resistance.

Rsenor = 22kΩ * (5V / Vout – 1)

Air Pollution Detector SchematicAir Pollution De

Step 6: MQ Toxic Gas Sensors

We used MQ-2 and MQ-9 gas sensors to measure toxic gasses including Propane, Butane, LPG and Carbon Monoxide.

The MQ-2 and MQ-9 are very similar to the MiCS detectors. They use a gas-sensitive resistor (SnO2) to detect concentrations of toxic gases and have an internal heating element to keep the sensor at the right temperature. The circuits we use for these devises are practically the same as the circuits for the MiCS sensors, except that we use a transistor rather than a resistor to regulate heater power in the MQ-9.

Refer to the solder board circuit diagram for mounting details. For the MQ-2 sensor, connect the pins marked A to the 5V power, connect the pin marked G to ground, and connect the pin marked S is connected to ground in series with a 47 kΩ resistor. For the MQ-9 gas sensor, connect the pin marked A to the transistor, the pin marked B to the 5 V power, the pin marked G to ground, and the pin marked S to ground in series with a 10 kΩ resistor.

For more detail: Air Pollution Detector




Current Project / Post can also be found using:

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