Hazardous Gas Monitor

Build a portable gas monitor to check for dangerous levels of hazardous gases in your home, community, or on the go and prevent your friends from lighting a cigarette during  a gasoline fight.*

This tutorial shows you how to build a web-connected “canary” monitor for three hazardous gases: Liquid Propane Gas (“LPG”), Methane (aka natural gas), and Carbon Monoxide (“CO”) . Using the Particle Photon microcontroller, the sensor readings are converted into parts-per-million (“PPM”) and uploaded to the data.sparkfun.com web service.

*Please note that this is solely a movie reference — gasoline fights should probably be avoided in real life.

Helpful Background Info!

1. How to set up the Particle Photon.

2. Pushing data to the data.sparkfun.com web server.

3. New to relays? Check out this a handy reference.

4. Here’s a helpful overview on the N-Channel MOSFET.

5. For powering the Photon, here’s a thorough guide on the Photon Battery Shield.

6. Highly recommended to peruse the datasheets for the three gas sensors.

Choosing a Battery!

The gas sensors used in this project require a fair amount of current, about 0.17 A each at 5V. To make the system portable, we’ll need a high capacity battery. One easy, and affordable, option is to use four (rechargeable) AA batteries in series. These batteries will last about 4 hours.

Another option is to use a lithium ion battery (“LIB”). LIBs have a higher capacity than AAs, but typically run at a lower voltage. If you go with this option, you may need to include a correction factor when you calculate the sensor value or boost the battery voltage with a transistor or other component.

The photo above shows a table with the approximate lifetime of a few different battery options.

If all of this sounds confusing, here’s a more thorough tutorial.


Here’s a Wish List that includes all the necessary components for this project!

Microcontroller and Accessory Components

Particle Photon microcontroller

SparkFun Photon Battery Shield

– One 2000 mAh Polymer Lithium Ion Battery

Surface Mount DC Barrel Jack

Barrel jack to USB power supply cable

One (1) Lamp Switch

– Optional: Male-to-Female JST connector cable

Gas Sensor Circuit

One (1) Project Case

– One (1) 4 AA battery case

– Four (4) AA Rechargeable Batteries

One (1) Toggle Switch (SPST switch)

Piezo Buzzer

Three (3) Red LEDs

– Three (3) 10 kΩ resistors

One (1) PCB

22 Gauge stranded wire

– Optional: Electrical connectors (3-5)

LPG (MQ6) Gas Sensor

MQ6 LPG Gas Sensor

Gas Sensor Breakout Board

– One (1) 4.7 kΩ resistor

– One (1) 5V Voltage Regulator

Methane (MQ4) Gas Sensor

MQ4 Methane Gas Sensor

Gas Sensor Breakout Board

– One (1) 4.7 kΩ resistor

– One (1) 5V Voltage Regulator

Carbon Monoxide (MQ7) Gas Sensor

MQ7 CO Gas Sensor

Gas Sensor Breakout Board

– One (1) 4.7 kΩ resistor

– One (1) 5V Voltage Regulator

– One (1) 5V SPDT Relay

– One (1) N-Channel MOSFET

– One (1) 10 kΩ potentiometer

– One (1) 10 kΩ resistor


– Soldering Iron

– Wire cutters/strippers

– Drill

– Screwdriver

– Epoxy (or hot glue)

Build it! Electronics

1. Solder gas sensor breakout boards to gas sensors. Orientation doesn’t matter, just be sure that the silkscreen (aka labels) are facing down so that you can read them (had to learn that one the hard way..). Solder wires to the gas sensor breakout board.

2. Solder three voltage regulators to the PCB board. For each regulator, connect positive battery output to the regulator input, and connect middle voltage regulator pin to ground.

3. Connect the LPG (MQ6) and Methane (MQ4) sensors.

For each sensor:

  1. Connect H1 and A1 to the output of one of the voltage regulators (recommended to use an electrical connector).
  2. Connect GND to ground.
  3. Connect B1 to Photon analog pin (LPG goes to A0, Methane to A1)
  4. Connect a 4.7 kΩ resistor from B1 to ground.

4. Connect the CO (MQ7) gas sensor.

*Aside: The MQ7 sensor requires cycling the heater voltage (H1) between 1.5V (for 90s) and 5V (for 60s). One way to do this is to use a relay triggered by the Photon (with the aid of a MOSFET and potentiometer) — when the relay is not powered, the voltage across H1 is 5V, and when the relay is powered the voltage across H1 is ~ 1.5V.

  1. Connect GND to ground.
  2. Connect B1 to Photon analog pin (A2). Connect 4.7 kΩ resistor from B1 to ground.
  3. Connect A1 to third voltage regulator output (5V source).
  4. Connect Photon 3.3V pin to positive relay input.
  5. Connect Photon Digital Pin D7 to left MOSFET pin, and a 10 kΩ resistor to ground.
  6. Connect middle MOSFET pin to relay ground pin. Connect right MOSFET pin to ground.
  7. Connect relay Normally Open (“NO”) pin to H1, and the Normally Closed (“NC”) pin to middle potentiometer pin.
  8. Connect right potentiometer pin to ground, and left pin to H1.
  9. Adjust potentiometer resistance until it changes the relay output to ~ 1.5V when the relay receives power.

5. Connect an LED and 10 kΩ resistor to each of the Photon digital pins D0, D1, and D2. Connect buzzer to Photon digital pin D4.

6. Connect toggle switch between battery pack and PCB board power. Recommended to include an electrical connector for the battery pack to make it easier to switch out batteries.

7. Connect lamp switch between LIB and Photon battery shield — recommended to use an extra JST cable for this to keep the LIB battery cable in tact (and make it easier to install the lamp switch).

8. Label wires!

Build a Case!

1. Drill hole for toggle switch on case lid.

2. Drill 3 holes in the case lid for the LED lights to shine through, and 3 holes for the gas sensors to have air contact. Adhere components on the inside of the lid.

3. Drill hole in the side of the case for barrel jack USB cord to connect to the Photon Battery Shield.

4. Drill two small holes on the side of the case for the lamp switch cable. Adhere lamp switch to side of case.

5. Label the LEDs with its corresponding gas sensor on the outside of the case.

6. Check electrical connections and, if everything is good to go, coat electrical connections in epoxy or hot glue.

Calculate Gas Sensor PPM!

Each of the gas sensors outputs an analog value from 0 to 4095. To convert this value into voltage, use the following equation:

Sensor Voltage = AnalogReading * 3.3V / 4095

Once you have the sensor voltage, you can convert that into a parts per million (“PPM”) reading using the sensitivity calibration curve on page 5 of the gas sensor datasheets. To do this, recreate the sensitivity curve by picking data points from the graph or using a graphical analysis software like Engauge Digitizer .

Plot PPM on the y-axis and V_RL on the x-axis, where V_RL is the sensor voltage. There is a lot of room for error with this method, but it will give us enough accuracy to identify dangerous levels of hazardous gases. Estimated error bars are around 20 PPM for the LPG and Methane sensors, and about 5 PPM for the CO sensor.

Next, find an approximate equation for the PPM vs. V_RL curve. I used an exponential fit (e.g. y = e^x) and got the following equations:

LPG sensor: PPM = 26.572*e^(1.2894*V_RL)

Methane sensor: PPM = 10.938*e(1.7742*V_RL)

CO sensor: PPM = 3.027*e^(1.0698*V_RL)

Program it!

First, set up a data stream on the [data.sparkfun.com service](http://data.sparkfun.com). Next, write a program to read in the analog value of each gas sensor, convert it to PPM, and check it against known safe thresholds. Based on OSHA safety standards, the thresholds for the three gases are as follows:

  • LPG: 1,000 PPM
  • Methane: 1,000 PPM
  • CO: 50 PPM

If you want to get up and running quickly, or are new to programming, feel free to use my code! Use it as-is or modify to suit your particular needs.

Here’s the GitHub page!

Here’s the raw program code.

Change the following in the code:

1. Copy and paste your data stream public key to the array called `publicKey[]`.

`const char publicKey[] = “INSERT_PUBLIC_KEY_HERE”;`

2.Copy and paste your data stream private key to the array called `privateKey[]`.

const char privateKey[] = “INSERT_PRIVATE_KEY_HERE”;

To monitor the Photon output, use the Particle driver downloaded as described in the [“Connecting Your Device” Photon tutorial](https://docs.particle.io/guide/getting-started/connect/photon/). Once this is installed, in the command prompt, type `particle serial monitor`. This is super helpful for debugging and checking that the Photon is posting data to the web.

Be a Citizen Scientist!

Now we get to test and employ our gas monitor! Turn the batteries for the gas sensors on using the toggle switch, wait about 3 – 5 minutes, then turn the Photon on with the lamp switch (the gas sensor heater coils take some time to heat up). Check that the Photon is connected to WiFi (on-board LED will slowly pulse light blue) and is uploading data to the server. Also check that the gas sensor readings increase when in proximity to hazardous gases — one easy, and safe, way is to hold a lighter and/or a match close to the sensors.

Once up and running, use the sensor to monitor for dangerous gas leaks around your home, school, workplace, neighborhood, etc. You can install the sensor in one location permanently, or use it to check gas levels in different locations (e.g. SoCal..).

Educator Extension!

This project is a perfect excuse for a hands-on chemistry lesson! Use the monitor to learn the fundamentals of various gases — what kinds of gases are in our environment, how are different gases produced, and what makes some of them hazardous or dangerous.

Study the local environment and use a lil’ math to record and plot LPG, Methane, and CO in specific locations over time to see how the levels change. Use the data to help determine what causes changes in the gas levels and where/when gas concentrations are the highest.


More to Explore!

Monitor hazardous gas concentrations around your neighborhood or city and use the results to identify problem areas and improve public safety.

Use Bluetooth, or your smartphone WiFi, to connect to the Photon and upload data to the web wherever you are!

Include other sensors, gaseous or otherwise , to create a more comprehensive environmental monitoring system.

Sound Reactive EL Wire Costume

Bring science fiction to life with a personalized light-up outfit! EL wire is a delightfully futuristic-looking luminescent wire that has the added benefit of staying cool, making it ideal for wearable projects. Combining sensors and a microcontroller with EL wire allow for a wide range of feedback and control options.

This project uses the SparkFun sound detector and the EL Sequencer to flash the EL wire to the rhythm of ambient sound, including music, clapping, and talking.




El Wire comes in a variety of colors, so pick your favorite(s)!


  • Article(s) of clothing

For a Tron-esque look, go for stretchy black material. Yoga pants and other athletic gear work great!

  • Belt
  • Old jacket with large pocket, preferably zippered or otherwise sealable.

The pocket will house the electronics. If you intend to wear the costume outdoors in potentially wet weather, choose a pocket that is waterproof (i.e. cut a pocket from a waterproof jacket).

  • Piece of packing foam or styrofoam (to insulate the sound detector).


Build it! Pt. 1

CAUTION: Although it is low current, EL wire runs on high voltage AC (100 VAC). There are exposed connections on the EL Sequencer board so BE CAREFUL when handling the board. Always double (and triple) check that the power switch is OFF before touching any part of the board. For final projects, it is recommended to coat all exposed connections in epoxy, hot glue, electrical tape, or other insulating material.

1. Test EL Sequencer with EL Wire.
Connect the inverter, battery, and at least one strand of EL wire to the EL Sequencer. (Note that the two black wires of the inverter correspond to the AC side.)
Be sure that the EL Wire lights up and blinks when you power the EL Sequencer on battery mode.

2. Solder header pins onto 5V FTDI pinholes on the EL Sequencer and onto the VCC, ground, and A2 input pins.

3. Solder header pins to the sound detector.

4. Connect sound detector to EL Sequencer via female-to-female breadboard wires (or solder wire onto header pins).
Connect the sound detector VCC and ground pins to the VCC and ground pins on the EL Sequencer. Connect the sound detector gate output to the A2 input pin on the EL Sequencer. If you are using the envelope and/or audio output signals, connect these to pins A3 and A4 on the EL Sequencer (more on this in the Program It! section).

Build it! Pt. 2

1. Make a protective casing for the sound detector using packing foam or styrofoam to prevent jostling or other physical vibrations (aka collisions) from triggering it.

Place sound detector on top of foam, outline the board with a pen, and cut out a hole in the foam for the detector to fit snugly inside. Also recommended to epoxy the wires onto the foam (but not the sound detector board).

2. Cut out a pocket from the jacket and sew onto the belt.

3. Put belt on, connect EL Wire to EL Sequencer, and place EL Sequencer in pocket pouch. Determine approximate placement of each EL wire strand based on location of electronics.

Build it! Pt. 3

1. Mark and/or adhere the base of the EL wire JST connector onto clothing, allowing the full length of the connector to flex. Be sure that the JST connector can easily reach the EL Sequencer.

2. Starting at the basse of the JST connector, attach EL wire strands to your chosen article of clothing.

Sew EL wire onto clothing using strong thread or dental floss, or use an appropriate fabric adhesive.
Prior to adhering the EL wire, it is recommended to use safety pins to determine placement of the EL wire on each article of clothing while you are wearing it. EL wire is flexible but not so stretchy, so give yourself some wiggle room.

It is also recommended to use separate EL wire strands on different articles of clothing to facilitate the process of taking it on/off.

Program it!  

1. Connect EL Sequencer to computer via 5V FTDI BOB or cable. 

2. Program the EL Sequencer using the Arduino platform; the EL Sequencer runs an ATmega 328p at 8 MHz and 3.3V.

3. Determine how you want to use the sound detector output(s) to control the EL wire. The sample program below utilizes the gate channel output to turn on the EL wire if there is a sound detected.

Sample Program:

// Sound Activated EL Wire Costume<br>// Blink EL Wire to music and other ambient sound.
void setup() {
  // The EL channels are on pins 2 through 9
  // Initialize the pins as outputs
  pinMode(2, OUTPUT);  // channel A  
  pinMode(3, OUTPUT);  // channel B   
  pinMode(4, OUTPUT);  // channel C
  pinMode(5, OUTPUT);  // channel D    
  pinMode(6, OUTPUT);  // channel E
  pinMode(7, OUTPUT);  // channel F
  pinMode(8, OUTPUT);  // channel G
  pinMode(9, OUTPUT);  // channel H
//Initialize input pins on EL Sequencer
  pinMode(A2, INPUT);
void loop() 
  int amp = digitalRead(A2);
  //If Gate output detects sound, turn EL Wire on
  if(amp == HIGH){
    digitalWrite(2, HIGH); //turn EL channel on
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);
    digitalWrite(2, LOW); //turn EL channel off
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);

This program is just one example of what is possible with the SparkFun sound detector. Depending on your needs, different responses can be achieved by using the “envelope” and “audio” outputs of the sound detector. The EL Sequencer can individually control up to 8 different EL wire strands using the three sound detector output signals, so there are tons of possiblities to customize your sound-activated outfit!

More information about the sound detector output signals:
The gate channel output is a digital signal that is high when a sound is detected and low when it is quiet. The envelope channel output traces the amplitude of the sound, and the audio output is the voltage directly from the microphone.

In the photo provided, the red trace corresponds to the gate signal output, the light green trace corresponds to the envelope signal output, and the dark green trace corresponds to the audio signal output.

Test, Secure, & Show Off!

Connect all components to the EL Sequencer (inverter, battery, sound detector) and place in belt pouch. Turn the system on, make some noise (e.g. clapping, snapping, or music) and check that the EL wire flashes when there is a sound.

If the outfit works as expected, secure all connections by coating them in a (thin) layer of epoxy. Let dry for at least 24 hours. Epoxy is a very permanent adhesive, so if you want to reuse any of the components, try other adhesives like hot glue or electrical tape (less secure, but adjustable and removable).

You can reduce the overall strain on individual connections by ensuring that wires are securely fastened to the belt and/or pouch approximately one inch (1″) from all connections. The goal is to allow the EL wire to flex while keeping electrical connections rigid, as the connections are the most likely point of breakage.

Wear your one-of-a-kind, high-tech outfit and go show it off to the world!

EL Wire Light Up Dog Harness

Whether it’s to keep Fido (or in my case, Marley) visible on an adventure or as an awesome all-year-round costume, a light up dog harness is an excellent accessory for your favorite pup.

EL wire is a great option for wearable lights. It stays cool, is flexible, and comes in lots of different colors. This design uses the SparkFun EL Sequencer to automatically turn on EL wire when it is sufficiently dark outside so you don’t have to worry
about locating Mr. Dog to turn the system on.

Here’s a video tutorial for this project.

Recommended Reading

If you are new to electronics, EL wire, or the EL Sequencer, or would like more information on the main components in this project, check out this tutorial.As this design also uses a lithium ion battery, I also recommend reading this tutorial to give you an overview on proper care and handling of lithium batteries.



  • EL Wire
    • EL wire comes in variety of colors, pick your favorite!

Harness Materials

  • Dog harness
    • A vest or backpack will also work.
  • Waterproof jacket with pocket(s)
  • Optional: Tupperware or other sealable plastic container


  • Safety goggles
  • Soldering Iron
  • Wire Cutter/Stripper
  • Epoxy (waterproof)
  • Scissors
  • Needle + thread OR fabric adhesive
  • Optional: Velcro

Build it! Pt. 1

**CAUTION:** Although it is low current, EL wire runs on high voltage AC (100 VAC). There are exposed connections on the EL Sequencer board so BE CAREFUL when handling the board. Always double (and triple) check that the power switch is OFF before touching any part of the board. For final projects, it is recommended to coat all exposed connections in epoxy, hot glue, electrical tape, or other insulating material.

1. Test the EL Sequencer with EL wire.
Connect EL Wire, inverter, and battery to EL sequencer.
Turn on power switch and check that the EL wire turns on (should be blinking). You can connect, and control, up to 8 different strands of EL wire.

2. Solder header pins onto 5V FTDI pinholes on the EL Sequencer.

3. Solder header pins to the “GND,” “VCC,” and “A2” pinholes EL Sequencer (right side).

4. Solder male end of breadboard wires to ambient light sensor. Coat exposed metal on the sensor in epoxy (do not coat actual sensor).

Note: Recommended to solder the pins on the bottom of the sensor so that the sensor can more easily be attached to the harness (found this out the hard way..).





Build it! Pt. 2 

1. Attach EL Wire to harness.
Sew EL wire onto harness with dental floss for a strong, durable bond. Can also use an appropriate fabric adhesive.For straps/buckles: leave about 1″ of unattached EL wire on either side of the strap/buckle.You can either wrap the ELwire for its entire length, or cut it and insulate the ends.2. Make a durable pouch for the electronics.
For a waterproof pouch, cut out a pocket in a waterproof jacket. I also included a small tupperware container to house the electronics in the pouch to further insulate and protect them from weather and dog conditions.

Build it! Pt. 3

1. Attach electronics pouch to harness.
Sew pouch onto top side of harness, or wherever is comfortable and practical for your pup. Recommended to put harness on dog to find a suitable location for the pouch.

2. Cut small holes on underside of pouch for the EL wire JST connector and the light sensor wires.

3. Attach and secure light sensor to harness. Recommended to put harness on your dog and mark location for light sensor so that it faces upward.
There was an ideal flap in the rainjacket pocket for me to cut a hole, push the sensor through, and epoxy the other side. You can also use velcro or sew the light sensor onto the pocket or harness, just be sure that it stays stationary and won’t get covered when the dog is moving.

4. If using tupperware, cut or drill holes in tupperware for EL wire JST connector and light sensor wires.
If you are not using tuperware, it is recommended to cushion the electronics and/or epoxy all connections (except the JST connectors) to protect them from your dog’s antics.

5. Connect EL wire and light sensor to EL Sequencer (through holes in the tuperware), then epoxy the holes to keep wires in place and maintain a waterproof seal.

Program It!

1. Connect EL Sequencer to computer via 5V FTDI BOB or cable. 

2. Program the EL Sequencer using the Arduino platform; the EL Sequencer runs an ATmega 328p at 8 MHz and 3.3V. 

3. Write a program to read in the analog value of the ambient light sensor, turn on the appropriate EL wire channels at a value that corresponds to low light, and turn off once the light sensor value is above the low light threshold.Here’s a sample program with a preset light threshold:

// EL Wire Dog Harness Program
// Turn EL wire on when ambient light is low.
// JenFoxBot
// Based on test sketch by Mike Grusin, SparkFun Electronics
void setup() {
  // The EL channels are on pins 2 through 9
  // Initialize the pins as outputs
  pinMode(2, OUTPUT);  // channel A  
  pinMode(3, OUTPUT);  // channel B   
  pinMode(4, OUTPUT);  // channel C
  pinMode(5, OUTPUT);  // channel D    
  pinMode(6, OUTPUT);  // channel E
  pinMode(7, OUTPUT);  // channel F
  pinMode(8, OUTPUT);  // channel G
  pinMode(9, OUTPUT);  // channel H
  // We also have two status LEDs, pin 10 on the EL Sequencer, 
  // and pin 13 on the Arduino itself
  pinMode(10, OUTPUT);     
  pinMode(13, OUTPUT); 
  pinMode(A2, INPUT);  
void loop() 
  int x,status;
  //If ambient lighting is too low, turn on EL wire
  if(analogRead(A2) < 50){
    digitalWrite(2, HIGH); //turn EL channel on
    delay(1000); //wait 1 second
    //Keep EL wire on until light sensor reading is greater than 50
    if(analogRead(A2) > 50){
      digitalWrite(2, LOW); //turn EL channel off
    Serial.println(analogRead(A2)); // Use this to check value of ambient light 
    digitalWrite(10, status);   // blink both status LEDs
    digitalWrite(13, status);

4. Check that the EL wire turns on when the ambient light is low, and turns off in bright light. 

Test it and Put it to Work!

Place EL Sequencer, inverter, and battery inside the pouch (and tupperware). Connect all components to the EL Sequencer and turn it on using battery power. Test it in low and bright light to ensure that it functions properly.

If system works as expected, put on dog and go exploring!As an added bonus, you can use the electronics pouch to store other small, non-magnetic items. Enjoy!