Arduino Powered Oder Neutralizer *Adult Supervision REQUIRED*

Create a device that detects the presence of flatulent odors and triggers an aerosol spray to mask and neutralize odors. Total cost under $100.

1. Automatic, electric air freshener
2. Male-Male silicone pin wires
3. Two wiring breadboards with pin inputs
4. Standard Resistor Set (Only one, 470 ohm resistor required for this project)
5. Micro USB breakout board
6. 4N35 Optocoupler
7. MQ2 Gas Sensor
8. Arduino UNO Programable Board
9. USB data cable

Simulate the methane sensor/Arduino circuit

1. Connect the analog pin on the MQ2 gas sensor to the analog input (A0) on the Arduino UNO (Green Wire)
2. Connect the GND pin on the MQ2 gas sensor to the GND rail (Black -) on the breadboard (Black Wire)
3. Use an external power supply (5V-2A) to simulate our USB-C breakout board. Connect the positive terminal (red) the power rail (red +) on the breadboard (Red Wire)
4. Connect all voltage pins on the MQ2 Sensor to the power rail (red +) to supply power to our sensor (Red Wires)
5. Add an FN35 optocoupler to the breadboard. Connect the GND pin to the GND rail (Black -) (Black Wire).
6. On the FN35 optocoupler, connect the collector pin to the button switch pin (Pink Wire) and connect the emitter pin to the second pin on the button switch (Black Wire). This way, the light from the LED inside the optocoupler activates a phototransistor, causing it to complete the circuit between the button switch, simulating pressing the physical button.
7. Wire the Digital Pin on the optocoupler to the digital input on the Arduino Uno (D2) (Blue Wire)
8. Add a 470 Ohm resistor between the resistor and the digital pin. The Arduino digital pin outputs a voltage of 5 Volts, which will damage the optocoupler. We need to add this resistor to lower the current and voltage going into the device within allowable levels. *Calculations attached as a photo*

Lines 1 - 5 (Defining our variables):

The gas sensor is connected to the A0 pin on our Arduino.

The optocoupler is connected to Digital Pin 2 on our Arduino.

Assign the gas level (threshold) that will trigger the optocoupler to send a signal to the air freshener

Define the pulse duration of the signal sent from the optocoupler (very short - roughly 100 milliseconds)

Establish a cooldown time so the air freshener does not continually spray (five minutes)

Lines 7 - 8 (Cooldown time function):

Tracking whether the system is in cooldown time

Stores the last activated time as a reference to insure the device is not active in cooldown time

Lines 10 - 13 (Void Loop 1):

Initial void loop

Establish the digital optocoupler pin as the output

Define the value of the optocoupler switch as LOW (Ensures the optocoupler is off at the start)

Allow the data values to be shown on the Arduino Serial Monitor

Lines 16 - 19 (Void Loop 2):

Define the gas sensor value as data received from the gas sensor analog sensor pin (Reading the data)

Print a line of the methane level reading " Methane Level: *Current Level Detected* "

Lines 21 - 25 (IF Loop):

The logic goes: IF the gas sensor value (gas detected) is greater than our allowable threshold, THEN a digital signal from the Arduino will activate the optocoupler (HIGH) which sends a 100 millisecond signal to the air freshener button. After 100 milliseconds, the optocoupler will turn off again (LOW). The serial monitor will also display a message to the user: "Methane Detected! Switch Activated."

Lines 27 - 29 (Enter cooldown time):

Once the methane is detected and the air freshener device triggered, cooldown time will begin and the time will be tracked until five minutes has passed.

Lines 34 - 36 (Checking if cooldown time [five minutes] has passed):

The logic is: IF the time the device triggered minus the previous trigger time is greater than the cooldown time [five minutes], THEN the cooldown time will reset and the air freshener will be ready to spray if needed. The serial monitor will alert the user "Cooldown complete. Ready for next detection."

Line 39 (Delay Time):

This adds a short delay [500 milliseconds] before the air freshener is ready to activate once cooldown time [five minutes] has passed.

1. Connect the two ground rails (black -) on the breadboard together with a wire. Connect the top of the ground rail (black -) to the first GND pin (GND) on the Arduino UNO.
2. Wire the MQ2 sensor according to our design schematic. The one we purchased has four pins, not six like our schematic. It includes a voltage pin (5V), ground pin (GND), analog pin (A0), and digital pin (D0). Wire the 5V pin to the positive (red +) rail on our breadboard, the GND pin to the negative (black -) ground rail on our breadboard, and the analog pin (A0) to the analog pin on our Arduino UNO (A2). We will not use the digital pin (D0). *NOTE: we are powering the MQ2 sensor with a Micro USB powered breakout board - this is safer for all devices than powering it with the 5V pin on the Arduino UNO*
3. On a separate breadboard, place the Micro USB powered breakout board. Wire the voltage pin (5V) to the positive rail (red +) on the MQ2 sensor breadboard. Wire the GND pin (GND) to the second GND pin on the Arduino UNO.
4. Place the optocoupler so that 3 pins are on each side of the breadboard. Wire the collector pin (pin 4) to one side of the button switch. Wire the emitter pin (pin 5) of the optocoupler to the opposite pin [same side] of the button switch. Add our 470 ohm resistor to the anode pin (pin 5) of the optocoupler. Wire the end of the resistor to the digital pin (D2) on the Arduino UNO. Wire the optocoupler GND pin to the negative rail (black -) on the breadboard. Connect the Arduino GND pin to the negative rail (black -) on the breadboard. *NOTE: We are powering the optocoupler with the digital pin (D2) on the Arduino UNO. It is NOT connected to the breadboard power rail. The digital pin sends a signal of 5V to the optocoupler, which we reduced to a safe voltage using our resistor*

Connecting the wires from the Collector pin and Emitter pin on the optocoupler to the air freshener button switch pins will require soldering. Use a soldering iron to connect the pin wires as shown.

1. Plug Arduino UNO into a computer using a data cable and plug in the Micro USB Breakout Board using a Micro USB Cable (an older android phone charger will work). If the above steps have been followed correctly, everything will work optimally.
2. Download and open the Arduino IDE software. https://www.arduino.cc/en/software/
3. Import your code to your Arduino UNO which will automatically run the program.
4. Open the serial monitor on the Arduino IDE so you can see the real-time data.
5. Test that the switch activates the air freshener when gas levels exceed your defined threshold. You can adjust the threshold as necessary. *NOTE: The air freshener must be powered on for the switch to trigger the release a spray of air freshener*

Begin testing different thresholds using the release of butane gas from a hand-held lighter, smoke from an incense stick - or you can release a fart into the sensor to test different thresholds! Remember you can shorten the cooldown time in your code if you require rapid testing.

I hope you have fun testing different gas contents, and thank you for viewing this tutorial! If you have any questions regarding the design or testing methods - feel free to comment below!