2. Methods

2. Methods
2.1 Equipments

  • 2X Rotary fans
  • 4X Wire mesh
  • 10X Totobobo Filters
  • 1X HEPA filter
  • 1X Air pump
  • 1X Air pump connector (for air tubes)
  • 1X long strip of air tubes
  • 1X Aromatics
  • 1X Arduino set [black]
  • 1X Small box (Water-based filter)
  • 1X Short metal box (to level the air pump)
  • 1X Roll of Cling Wrap
  • 1X Disposable container for MQ7 carbon monoxide sensor
  • 1X Packet of bluetack
  • 1X Room for experiment
  • 1X Small non-flammable box
  • 1X Large transparent container (for the air purifier system itself)
  • 1X Screws (one packet)
  • 1X Nuts (one packet)
  • 4X Screw driver
  • 4X Penknives
  • 1X Hot glue gun
  • 1X packet of glue sticks
  • 36X pieces of paper
  • 1X roll of duct tape
  • 1X wire stripper
  • 2X 3-pin plug head
  • 1X long strip of insulated wire
  • 2X wire connectors
  • 1X large wooden box

2.2 Diagram

Screen Shot 2014-08-26 at 9.48.44 PM.png

2.3 Procedures

2.31 - Connection of rotary fan wires

  1. Cut a suitable length of the insulated wire (Long enough to connect from the air purifier system to the 3-pin plug)
  2. Strip both ends of the insulation
  3. Follow the instructions on the paper on top of the plug to connect the individual wires to the pins
  4. Connect the other end of the insulated wires (already stripped) to a wire connector using a screw driver
  5. Strip suitable lengths of wires of the rotary fan
  6. Connect the wires of the rotary fan to the wire connector using a screw driver
  7. For the two rotary fans, we need to connect each of them to a 3 pin plug so that we can supply electricity to them through the socket. To do this, we will get cable wires and trim off a decent length of the insulation rubber on each end. Then we will strip the wires inside the cable wire and connect them to the 3 pin plug according to the arrangement shown below.

  1. After one end of the wire is connected to the 3 pin plug, we will connect the other end to one opening of the wire connecter. The other opening of the wire connecter is where we will connect the wires of the rotary fans. We will repeat all of this twice since we have two rotary fans.

2.32 - Building the air purifier

  1. Acquire all the necessary equipments (refer to equipment list)
  2. Attach 2 wire meshes to both sides of the rotary fan using bolts and screws
  3. Cut 1 hole at the side of one large transparent container with considerations to the size of the wire meshes and rotary fans.
  4. Create 4 holes for the screws and bolts to screw the rotary fan into place (The size of the holes should be slightly smaller than the size of the screws)
  5. Attach the rotary fan to the large transparent box using screws and bolts
  6. Cut other holes which are necessary (For tubes to go through to the air pump, the hole for the wire of the air pump to reach the socket)
  7. Cut a hole in the piece of cardboard to fit the HEPA filter and ensure that this piece fits the large transparent container. These cardboards are reused from old card boxes which ensures the materials used are more environmentally friendly.
  8. Attach the HEPA filter to the cardboard before attaching the cardboard to the center of the large transparent container. Make sure that it is secure and use hot glue guns to secure the HEPA filter into place. Ensure that there are no leakage of air by using the hot glue guns to cover all holes.
  9. Place a small metal box in the next section. We will use a metal box as it is sturdy, so it can support the weight of the air pump, and it has been reused.
  10. Place the air pump in the next section of the system on top of the metal box.
  11. Connect the wire (leading to the socket) to the socket and ensure that no air escapes that hole by using cardboard to cover the huge hole and hot glue gun and blue tack to secure the cardboards in place and also to ensure no leakage.
  12. Place the 6 tubes from the air pump through the 6 holes created earlier and place them into the green box. Ensure that there are no leakages by making sure that the tubes fit into the holes tightly. (Tight but not till no air can flow through)
  13. Cut 6 holes in the lid of the green box at the side (water based filter) for the six air tubes to go through into the water.
  14. Cut another 4 holes in the green box in considerations to the size of the screws which are going to screw the second rotary fan into place
  15. Cut 1 hole at the in the centre of the green box with considerations to the size of the wire meshes and rotary fans.
  16. Fill the green box with water, ensuring that the water level does not exceed the the height of the base of the air pump. Ensure that the water will not come into contact with the water.
  17. Add aromatics.
  18. Using duct tape, ensure that the entrance of the tube which the air escapes from is under water.
  19. Use the cover of the whole transparent box to cover the whole system in the large transparent box.
  20. Ensure that no air can escape each section of the system and of the whole experimental area (room).

Part 2.33 - Preparing the Setup

  1. Attach Totobobo masks onto one side of the wire mesh of the first rotary fan
  2. Place the device into the large wooden box
  3. Place paper inside a small unflammable box
  4. Place the small non-flammable box inside the room, ensuring that the flame will not be able to reach the device or any wires
  5. Close all windows and openings of the room so that no smoke will exit the room
  6. Burn the paper until all of it is burnt
  7. Turn on the MQ7 sensor that is hooked up to the laptop
  8. Turn on the air purifying device
  9. Leave the room and close the door
  10. Cover the area between the door and the floor with a wet cloth so that no smoke can escape the room
  11. Note down the readings from the MQ7 for 30 minutes for each experiment

Part 2.34 - The carbon monoxide sensor

1. The gas sensing layer on the MQ7 is made of Tin dioxide (SnO2), which has lower conductivity in clean air. The conductivity increases as the levels of carbon monoxide rise (Mikro Elektronika, 2014). Because of this, the higher the carbon monoxide level is, the lesser the resistance will be and the smaller the reading of the MQ7 will be.

2. This is the code that we will use to programme the arduino:

float Ro = 10000.0;    // this has to be tuned 10K Ohm
int sensorPin = 0;  // select the input pin for the sensor
int val = 0;        // variable to store the value coming from the sensor
float Vrl = 0.0;
float Rs = 0.0;
float ratio = 0.0;

void setup() {
Serial.begin(9600);      // initialize serial communication with computer
// analogReference(EXTERNAL);

// get CO ppm
float get_CO (float ratio){
 float ppm = 0.0;
 ppm = 37143 * pow (ratio, -4);
return ppm;

void loop() {
val = analogRead(sensorPin);     // read the value from the analog sensor
Serial.println(val);             // send it to the computer (as ASCII digits)

Vrl = val * ( 5.00 / 1024.0  );      // V
Rs = 20000 * ( 5.00 - Vrl) / Vrl ;   // Ohm
ratio =  Rs/Ro;                      
Serial.print ( "Vrl / Rs / ratio:");
Serial.print (Vrl);
Serial.print(" ");
Serial.print (Rs);
Serial.print(" ");
Serial.print ( "CO ppm :");


3. The formula shown below is the formula for linear equations (y = mx + c). The coordinates of the graph below have been plotted in a logarithmic graph. By finding two different points and their coordinates on the graph, we can determine the gradient of the linear graph (m). Once we have determined the m value, we can sub in the y and x coordinates for when the surrounding air has 100PPM of carbon monoxide (1 and 100 respectively) and find the c value. That will lead us to our final equation which is included in the picture below.
Screen Shot 2014-08-24 at 4.48.25 PM.png

4. Ro is 10K ohm as the resistor that we are using is a 10K ohm resistor. Rs is determined by the equation “Rs=20000*(VC-VRL)/VRL”. This equation is included in the code so that the computer can determine the Rs value. VC is the voltage that the MQ7 sensor is receiving which is 5V from the arduino.

5.  VRL is determined by the equation “VRL = val * ( 5.00 / 1024.0 )”. “val” is the value coming from the sensor. This equation is also included in the code so that the VRL value can be subbed into the equation that determines Rs. By using these equations, the computer will help to calculate everything before printing out the PPM value of carbon monoxide levels.

6. The MQ7 carbon monoxide sensor has six pins, two ‘A’ pins, two ‘B’ pins and two ‘H’ pins. The ‘H’ pins are the heaters and connecting a voltage to one of the ‘H’ pins will keep the sensor hot enough to function properly. Connecting five volts at either the ‘A’ or ‘B’ pins causes the sensor to emit an analog voltage on the other pins. A resistive load between the output pins and ground sets the sensitivity of the detector. Below is a circuit diagram of how we will connect the MQ7 sensor to the arduino.

Screen Shot 2014-08-31 at 4.10.58 PM.png
2.35 - Experiment

  1. Light up the paper in the small non-flammable box
  2. Test the carbon monoxide level in the room using the MQ7 carbon monoxide sensor
  3. Record the reading of the carbon monoxide levels
  4. Turn on the Air purifier
  5. Leave the room and close the door. Cover the area between the door and the floor with a wet cloth so that no smoke can escape the room
  6. Allow the air purifier to purify the air for 30 minutes
  7. Record the readings of the carbon monoxide sensor for that 30 minutes
  8. Repeat steps 1 - 7 for each experiment with different numbers of paper (6, 12 and 18 respectively)
  9. Plot a graph of the change in carbon monoxide levels in the room for each experiment
  10. Draw a conclusion
  11. See if any changes are to be made in the system and improve on the system

2.4 Risk and Safety

The potential risks are:
  • We have to produce harmful gases or use chemicals to create an atmosphere to test our prototype. Doing this might harm our health if we accidentally breathe in the harmful gases and pollutants. To protect ourselves from the gases, we can stay a safe distance away from the atmosphere we created so that we will not accidentally breathe in the harmful gases. We may also wear the Totobobo masks to further protect us from the harmful gases. The different types of harmful gases are: PM10, PM2.5, Sulfur Dioxide, Nitrogen Dioxide and Carbon monoxide. Though these gases will not actually kill anyone, they may cause serious health issues if inhaled by people.
  • To see if our prototype is effective, we also have to add dust to our atmosphere. However, some people may have sinus or allergies and the dust created to test our prototype might affect those people. We can prevent this by warning the people who have sinus and allergies, and also have the needed medication for their sinus and allergies on standby. They can also take extra precaution by wearing disposable masks or the more effective Totobobo masks.
  • When the blades of the rotary fan is spinning, we might accidentally cut our own finger, thus when handling the rotary fan, we would not turn on the electricity when we are holding it. There will also be a wire mesh around the perimeter of the rotary fan so that we will not accidentally touch the moving blades.
  • When changing the water in the water-based filter, we might accidentally spill the water on wires. The sockets may be turned on and there might be electricity running through the wires. Hence, the spilled water may cause a short circuit under the condition that the wires are broken. We can ensure that this will not happen by checking the conditions of all the wires before building our air purifier and also take extra caution while changing the water in the water-based filter. We are also separating our main air purifier system from the water based filter so reduce the risk of wires coming into contact with water and short circuiting it.
  • When burning the paper, we may accidentally burn ourselves or set the whole system on fire. Hence, we have to make sure that we have a fire extinguisher at the ready at all times in case the flame goes out of control and causes the whole set up to catch on fire and have a water running tap nearby and a first aid kit in case we get burned.
  • We may accidentally cut ourselves while cutting the holes in the box. We will prevent this by being extra careful while cutting.

2.5 Data Analysis:

We will place the air purifying device into a large wooden box meant for testing. Since there is space above the air purifying device, we will place the MQ7 carbon monoxide sensor above the first box of the device. All the wires of the electrical components, including the MQ7 sensor, will be tied with a cable tie and arranged according to one corner of the wooden box. When everything is placed inside of the box, we will seal the opening of the box up with cling wrap and duct tape. We will also leave a hole in the cling wrap near the side of the box so that we can put the non-flammable container in and quickly close up the wooden box without any inconvenience caused. This is how our experimental set up should look like:

Screen Shot 2014-08-31 at 8.38.10 PM.png

We will burn the a few pieces of paper according to the experiment’s requirements and put out the fire just before placing the paper into the container. We will then close the container and collect the smoke produced by the burning paper. Once we are sure that the device is ready to be turned on and that the cling wrap is put perfectly into place, we will open the container, quickly put it into the box and seal up the hole with more cling wrap and duct tape. We will let the smoke circulate around the wooden box until the readings read by the MQ7 carbon monoxide sensor is stabilized, then we will turn on the device and start the timer for thirty minutes, not forgetting to note down the data from the MQ7 carbon monoxide sensor with intervals of five minutes.

Using the data collected, we will plot a graph for the carbon monoxide levels against time [at intervals of 2.5 minutes]. With the graph, we will be able to see how efficient our device is.

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