What does math have to do with feminism?

I run a YouTube channel with plethora of nerdy videos about science, technology, engineering, and mathematics, or STEM for short. It is my goal to make these subjects fun, accessible, and normalized for women and gender non-conforming folks. As a recent viewer asked: Why?

I truly wish that me being good at math and science had nothing to do with feminism and inclusion. I want to do math and physics and engineering because I love them! Unfortunately, throughout my education and career, I have experienced the full spectrum of sexism. The same goes for every other woman and other visible minorities, which means it is especially bad for women and gender non-binary folks of color.

So what does this mean? It means that women and other visible minorities do not see themselves in these fields, which means that is less likely that these folks will pursue careers in this fields. It means that women and other visible minorities are told from very early ages that they are not good at STEM subjects and that it’s “okay” if they don’t understand, which prevents them from trying to learn from the very beginning. It means that women and other visible minorities have to constantly prove that we are capable of being good at STEM subjects.

Here’s a specific example: when I was called into a professor’s office in college, my peers told me it was because he wanted to sleep with me. In reality, it was because I was the top of our physics class and, as a result of my hard work, he offered me a research opportunity. My peers’ comments made me extremely uncomfortable and it meant that they did not see me as a hardworking and high-achieving student, they saw me as an object. Their attitudes planted a seed that has been watered every day by others and our society as a whole until it turned into a monstrous weed that threatened to overcome everything else I’ve worked so hard to build. It has taken me as much time and energy to rip up that weed as it has for me to learn these subjects (which is to say: a LOT). And it is work that is never over, because the sexism never ends.

Generally speaking, the constant barrage of sexism in STEM fields only gets worse as women get higher up and farther into their career, which is a huge reason why the small percentage of women who succeed in STEM oftentimes end up leaving these fields.

I don’t want to have to fight to do the things I love and am good at, it is waste of my energy and my time that could otherwise be spent on learning and doing. Sadly, I do not have a choice. My presence in STEM makes me subject to regular sexism, both in person and online. It is not possible to “ignore” sexism, especially when it results in fewer opportunities and recognition.

But what I can do is to help erase these useless and erroneous stereotypes that hold all of us back. I can be a positive role model who is good at STEM subjects and I can create spaces and opportunities for other women and visible minorities to improve representation in STEM fields. Until these fields are equal, I will continue to focus on those folks who have more obstacles and fewer opportunities.

We are all in this society together, and we will only overcome the challenges facing our world if we create space for diverse voices and ideas from the full and beautiful spectrum of humanity. Feminism is about inclusion and equality, and it is as good and healthy for women and non-binary folks as it is for men. So please, help me to open those doors that have been shut and locked for thousands of years so we can welcome every single person to the table.

We cannot fix everything, but we can certainly build a bigger table.

Science Research is Important! Here’s why.

Pierre Teilhard de Chardin, a paleontologist, geologist, philosopher, and Jesuit priest, wrote: “The history of the living world is an elaboration of ever more perfect eyes in a cosmos in which there is always something new to be seen.” Humans have long sought answers to the mysteries of the natural world. Eventually, our curiosity helped us to develop the scientific method.


Today, support for basic scientific research in the United States is shrinking. There are fewer opportunities for careers in research, and we are attracting less and less qualified students both domestically and abroad. This is alarming as the neglect of basic research could be disastrous for our society and our species.


As stated by Daniel Kleppner, a physicist at MIT, “If our civilization succeeds in learning to live in harmony with the natural world, science will have played a crucial role in the transition.” Right now, we must convince Congress of this urgent fact. There is much to be optimistic about: the numbers of scientifically literate citizens and members of Congress are growing. But we must speak up about the importance of basic research if we are to save it.

Image result for climate change

Climate change is a serious and life-threatening hurdle for our species. We need new ways to deal with the rapid change in our climate and in our ecosystems. In fact, the latest report from the Intergovernmental Panel on Climate Change (“IPCC”) concludes “that previous reports erred in being to cautious: The time to stem the flow of greenhouse gases is shorter than had been estimated. We face the possibility of a runaway situation in which an increase in global temperature feeds back to accelerate global heating. Such a process would lead to a massive change in climate and a catastrophic elevation of sea level. We face a threat to civilization.”

Basic research has brought us tools and techniques that allow us to measure data critical to understanding Earth and the cosmos. For example, GPS few out of simple curiosity about general relativity, studies of atomic nuclei brought us the invention of MRI, and experiments of molecules in space lead to the development of the laser.

Yayy science for bringing us lasers!!
Humanity needs basic research to explore the mysteries of our existence as well as to ensure our species continues to thrive in harmony with nature. We need scientists from all backgrounds to bring new ideas and novel solutions to the table. We need you, dear reader, to ask your most burning questions and to seek answers using whatever tools and resources are available. And of course, to promote science in the classroom, in the community, and in Congress.


Please consider calling your local, state, and federal representatives and urge them to support funding for basic scientific research. Our very lives depend on it.



The inspiration for this post:

FoxBot Founder/CEO at 2019 Ann Arbor Creativity and Making Expo!


Hello to our Maker friends in the Midwest! We are so excited that our founder/CEO, Jen Foxbot, is a featured speaker at the Ann Arbor Creativity and Making Expo on May 19th!

Fox will be doing a live demo involving Arduino and Excel as well as filming a Math Mondays episode at the Ann Arbor District Library. If you’re in the area, swing by, say hello, and learn some cool tech tricks!

To learn more, please visit the AACME website.

Hope to see y’all there!!

Build & Play Robot Mini Golf!


Create, build, and play an obstacle course for Brush Bots! This is an activity for all ages that teaches the basics of circuits and design thinking while encouraging and inspiring creativity, discovery, and collaboration. Most importantly, it’s super fun! (But seriously though, watch the video it’s adorbs and will make you smile)

This tutorial will show you how to build (and source parts for) a Brush Bot, how to design and build mini golf inspired obstacles, and how to use the design thinking process to create a Brush Bot that can accomplish each of the obstacles. Go forth and build your own Robot Mini Golf course!!



Tools & Materials


  • Scissors
  • Hot glue gun(s) + hot glue sticks
  • Wire cutters/strippers
  • Masking Tape


1. Electronics

2. Brush Bot Body & Feet

Since there are tons of ways to build the body, no list is absolute. Here are some suggestions (upcycling materials are highly encouraged & also cut down on cost!):

  • Toothbrush bristles
  • Styrofoam/plastic/paper cups
  • Paper plates
  • Cardboard
  • Tupperware
  • Toothpicks and/or wooden skewers
  • Popsicle sticks
  • Styrofoam pieces

3. Obstacles

  • Cardboard, cardboard, and more cardboard!
  • Art supplies
  • And maybe throw in some electronics in there also (see Step 4) 🙂


What the heck are Brush Bots??

Brush Bots, or Bristle Bots, are the simplest possible form of a robot: a motor with a counterweight and a battery attached to simple body. The counterweight causes the motor to shake, which, in turn, causes the body to shake.

The name “Brush Bot” comes from
a common design that uses toothbrush bristles as the “feet”. The term has been adapted to refer to any simple robot based on the counterweight motor design. Another super fun variation are Art Bots, which use markers or other materials to draw while they wobble around!

There are tons of ways to build a Brush Bot. A couple of approaches are shown in the photos. What other ways can you invent to build a Brush Bot?


Building the Obstacles

My obstacles were inspired by mini golf and through my experience in teaching Brush Bots and seeing various approaches from students and educators. I wanted obstacles that would be fun, accessible, and interesting for kids and adults, so I came up with four obstacles of varying difficulty.

Obstacle 1: Enter the Arena

Starting from 1 – 2 feet away, the Brush Bot must enter the opening to an arena. This can be made by marking an arena with tape, or by building a simple fence from cardboard.

Obstacle 2: Spiral Maze

The spiral maze is a crowd favorite and is a great obstacle for younger kids to tackle. Build the spiral maze by scoring a long piece of cardboard (~ 4 feet), then gluing it in a spiral pattern on a 2′ x 2′ cardboard square.

I decorated mine to look like a galaxy by spray painting the outside gold and the inside black, then gluing glow-in-the-dark stars on the inside.

Obstacle 3: Ramp

Although easy to make, this obstacle has proved to be the most challenging. I recommend using a low incline (less than 15 degrees) and adding a rough surface (e.g. sandpaper) on top of the cardboard.

Build the ramp by cutting out two identical triangles and then adhering a cardboard square on top.




Obstacle 4: Robot Head

By far the most fun, but a bit more complicated. I wrote a quick Arduino sketch to move a servo motor and added an IR breakbeam switch to trigger some LEDs when a Brush Bot goes into the mouth.

Recreate or modify this Robot Head or create your own whimsical obstacle!

Building the Brush Bot(s)!

1. Dismantle and gut an electric toothbrush! Your mission: find the motor.

For the Assure-brand “Soft Bristle Electric Toothbrushes” that you can get at the Dollar Store (just $1 woot woot!), twist off the bottom, pull out the battery holder, and pull out the motor. You may need to tap (or hit) the open toothbrush on the floor to get the motor out, or (gently) use pliers to pull it out.

2. Grab (or build!!) a battery box, and connect the positive side (red wire) to one of the motor leads*.

3. Connect the negative side of the battery box (black wire) to the other motor lead.

Orientation doesn’t matter — try switching them and see what happens!

4. Design and build a body for the lil ‘bot and give it a way to move. Iteration through different designs is recommended and encouraged!

Some common and easy ways to make the Brush Bot move are to use toothbrush bristles, toothpicks, or popsicle sticks to make legs/feet. Try different objects and object placements to see what happens.

*The motor leads are those gold tabs with holes by the white cap of the motor.


Conquering Obstacles W/ Design Thinking

Design Thinking is a problem-solving method. Traditionally, it’s applied for design of hardware and software products in various engineering disciplines, but this process can be applied to pretty much any aspect of life. The Design Thinking process comes in variety of flavors, here is a common breakdown:

1. Design: Who is your audience? What, or who, are you designing for? What are constraints for your product/project?

2. Ideate: How can you solve this problem? Come up with at least 3 – 5 different approaches — impossible solutions are totally acceptable in this phase.

3. Prototype: Choose one of your (possible) solutions and build it.

4. Test/Observe: Test your prototype and observe how it behaves. Does it solve your problem? If not, what’s wrong with it? If it does, can it be done in a simpler or easier way?

5. Adjust: Change your prototype based on your testing and observations.

Repeat steps 3 – 5 until you’ve arrived at a solution that solves your problem, satisfies your audience (or teacher), and meets any design constraints.

For Educators:

You can go through the design thinking process before, during, or after the workshop. One of the benefits of having obstacles to conquer is that it motivates students to naturally go through this process without having to sit and think about it.


Compete & Add Prizes

That’s it! You’re ready to tackle and challenge your students, friends, and/or family to a game of Robot Mini Golf!

A bonus feature would be to add prizes for anyone who successfully completes either one or all of the obstacles. My favorite method is to give out small prizes (e.g. stickers or buttons) to anyone who builds a Brush Bot that completes at least one of the obstacles, and a larger prize for anyone whose Brush Bot successfully completes all of the obstacles. This is a great way to adapt this into a workshop for folks of all ages — older kids and adults can try to conquer all of the obstacles while the younger kids still get to participate and have a blast! 😀

Please feel free to share your Robot Mini Golf stories in the comments! Would lovelovelove to hear anecdotes of how this activity went with students and/or to see photos of your unique Brush Bot(s) and obstacle course creations!

A Few of Our Favorite Brush Bots


Make Custom (& Inexpensive) Circuit Blocks!

Create, build, and play with your very own LEGO-inspired circuit blocks! Explore the basics of electricity and circuits, discover how sensors work and use ’em to design your own experiments, and incorporate upcycled materials to improve on your materials-sourcing & MacGuyver-ing skills! That old gum wrapper? Make it into a resistor or a switch!

But seriously, this is a super fun (and inexpensive) project/toy/game to teach electronics to kids (and adults!) of all ages and experience levels. The total cost of this project is under $30 and it takes about 2 hours to design and build.


Ok.. so where do we start?

First we need a base, the circuit block itself. This design uses breadboards* as the circuit block bases. I chose mini color breadboards so that each color denotes a specific type of electronic component (see next section). These are super cheap, typically less than $1 per board. Follow my design or create your own!

For each breadboard/component, we also need at least two or more breadboard wires (or 22 or 24 stranded wire), so for 20 breadboards with a single component we need 40 or more breadboard wires.

*Breadboards are non-edible, inexpensive prototyping boards for electronics projects. See photo above for a quick illustration of how breadboards work, or check out this tutorial.


Gather Electronic Components!

If you happen to have an assortment of electronic components around, gather them up and go through them to find the most choice pieces — we want components with only two leads, like simple motors, fans, LEDs, resistors, capacitors, etc. Check out websites like SparkFun or Amazon and search for electronic components.

Hey, wait, where can I get this stuff for free??

Dig up that box of broken electronics in your garage and see what you can find inside the electronics!

The best sources for components are electronic toys that move and/or make noise, speakers, telephones, and other medium-sized electronics.You’ll need wire cutters and pliers to remove the pieces, be sure to keep the legs intact so they can easily connect to the breadboard.

Avoid smartphones, tablets and laptops since the circuit components are suuuuper small and difficult to attach to a breadboard (unless that’s what you’re going for, then extract away!). For safety reasons, avoid appliances (e.g. microwaves, televisions, refrigerators, etc.), and do not use capacitors that are larger than a child’s thumb.


Build the Circuit Blocks!

The breadboard assortment I got included red, blue, white, green and black, mini breadboards. I broke up the colors into the following categories and components:


Red boards (power devices): One 1 W solar panel, one 9V battery clip, one 2 AA battery box, and two coin cell cases.




Blue boards (simple active): one motor w/ propeller, six LEDs of different colors (three per board), and one transistor (the transistor is pretty tricky — I’d recommend replacing this with another motor).




Green boards (sensors): one photoresistor, one buzzer/piezoelectric sensor, one peltier junction, and one capacitive sensor (this didn’t end up working, so replace it with a pressure sensor or other cool, two-lead sensor).




White boards (simple passive): six resistors of varying values (three per board), two (small electrolytic) capacitors of different values, and one potentiometer.





Black boards (electromechanical): Two pushbutton switches of different sizes/types (one per board), two toggle switches (single board), and one cooling fan.




To build each circuit block:
Connect each component to the first rows of each breadboard (be sure they aren’t shorted — should be on either side of the breadboard), and hot glue the wires into place. Remember to label which side is positive and which side is negative! Another fun option is to make labels for each component.


Plug & Play!

You’re ready to start building circuits and teaching other people the basics of electronics! Start simple, then add in more components to explore their function and see how they affect your circuit.

Here’s an example progression exploring different ways to light up an LED:

1. Use a coin cell to light up an LED.

Exploration questions: Does orientation matter? Where do the wires need to connect to the breadboard?

2. Use the solar panel to light up an LED. Move the panel into the shade (or cover it with your hand), and see how the LED brightness changes.

Exploration questions: How does the brightness of the LED change when you cover the solar panel? Why does this happen?

3. Use a coin cell and potentiometer to adjust the brightness of an LED.

Exploration questions: What do you notice? Does it matter how we connect the potentiometer?

4. Use a coin cell and a photoresistor to adjust the brightness of an LED.

Exploration questions: What do you notice?. Does it matter how we connect the photoresistor? How could we use the photoresistor in an experiment?

Build your own sequences to teach folks about specific circuit components or sensors, or use them as a fun & educational free-time project!

Make a Light-Up Holiday Card!

Light-up cards incorporate two of the best worlds of making (electronics and crafts) with the added bonus of making somebody smile. Heck yes!

Here’s my approach to light-up cards and my favorite recent discoveries: pop-ups and cotton balls.

Read time: ~ 5 min.

Build time: ~ 30 min -1 hr (mostly crafting the card)

Cost: < $5



Gather up the following materials:

  • One or more LEDs!
  • Copper tape (~ 20″)
  • One coin cell
  • One paper clip
  • One pushpin
  • Colored paper
  • & any other craft materials your creative heart desires!


Build the Circuit!



1. Cut out a pocket for the coin cell.




2. Add copper tape to cardstock!

Stick 2″ of copper tape just above the battery pocket, so that the bottom of the battery rests on top of it. This is the negative (-) side of the circuit.

Stick another 2″ piece of copper tape on the underside of the pocket, so that it touches the top of the battery. This is the positive (+) side of the circuit.


3. Add a switch!

Cut a small line at the end of the copper tape, push paper fastener through the slit and hook the paperclip under the paper fastener (it might also help to add copper tape to the end of the paperclip). This makes an “on/off” switch!



4. Connect the LED!

The longer LED leg connects to the positive side of the circuit. The shorter leg connects to the negative side of the circuit. Be sure that these two sides of the circuit do not cross, or it “shorts” the LED and drains the battery.



Design & Make the Card!

1. Plan out where the light is going to go!

This is super crucial if you want the light to be in a specific spot, like the top of a tree, as a nose, etc. It’s helpful to make a super simple drawing of what you want before you try, or at least have extra materials on-hand for second (or possibly third) versions. Check all the things before you glue stuff down.

2. Craft the card!

Since it’s the December holiday season, I’m making a bunch of holidays cards for friends, woo! I like incorporating re-used (or upcycled) materials, so for this card I cut out the cover of an old calendar and folded the edges under to make it 3D (oooohhh now we’re gettin’ fancy!).

Another fun option are pop-ups! Cut out thin strips (~ 1/2 inch) and fold them accordion-style, then use ’em to prop up your cutouts and drawings!

3. Add in the LED!

You can either hide the circuit under the cover, or inside the card. For this card, the circuit slips under the cut-out, and the LED, covered by a lot of cotton balls, sticks out the top to light up the clouds!



Final Touches & Beyond!

Close the switch to the LED and stand in awe at your awesome creation! Write a heart-felt note on the inside and give it to your favorite family member/friend/coworker/neighbor/etc!!

There are tons of other ways to make the LED circuit! The photo to the left shows a method using magnets (ohhhh magnets!). What other ways can you come up with to make the circuit? Post your creations in the comments below!! 😀

Prototyping Magnetic Boots!

Walking across large, metal pipes in search of urban adventure, my inner voice joked, “Hey, magnet shoes would be handy right about now.” Well, no arguing with that! Off to build my very own magnetic shoes!

This tutorial gives an overview of my build process for a magnetic boot prototype in hopes of inspiring you to build and test your own whimsical ideas! ‘Cause seriously, making ideas come to life feels like a superpower.



— Sturdy Boots
These had to secure my feet (aka no slipping out) and withstand my body weight. I found a pair of sturdy (although rather large) snowboard boots at a local thrift store which work as a first prototype.

— Rare earth (neodymium) magnets
Small, thin-ish (< 1/4″ thick) magnets with a 10 – 15 lbf rating (see previous step).

— One screw per magnet (or per magnet hole)
Use screws with a length shorter than the sole of the shoe (so they don’t poke your lil’ feetsies.. or add some sort of rubber sole inside).

— Suggestion: One washer per magnet
Supposedly, the washer helps increase the magnetic field of the exposed surface. I haven’t calculated this or done any serious research, so at this point it’s just a design suggestion.



— Ruler

— Pen/pencil.

CNC Router and a 3/4″ drill bit


Build Process!

1. Level bottom of the boot with a CNC router (or other available method).

Clamp the boots to the CNC table with the bottom facing up — a piece of wood was helpful to keep the boots straight.

Set the zero point of the CNC to be the lowest point on the sole of the shoe, then use a large bit (ours was 3/4″) and level the sole of the shoe to the zero point.

2. Mark boot with tape for location of magnets.

3. For each magnet, drill in screw, magnet, and washer into the bottom of shoe.


To test the boot, I stuck it on a roof beam and pulled downwards. I added more magnets and repeated this until I couldn’t pull the boot off by hand, then (slowly) tried to hang from it.

Lessons learned during testing:
1. I ended up using waaay more magnets than I thought, so it is probably worthwhile to calculate how the individual magnet fields are adding together.

2. Magnets need to be level to maximize the total magnetic field strength.

3. There is a limit to how close you can place each magnet depending on the shape and size of its magnetic field. Smaller, round magnets are easier to work with than large, rectangular magnets.

4. Don’t place magnets close to parking passes (or other electronic devices). Also keep them far, far away from large containers of screws.

Results & Next Steps!

At this point, my magnetic shoes are more magnetic “gloves” (lol thanks @jayludden :D). But! I can successfully hang from one boot, so the concept works!

The lessons learned from testing will help improve this prototype design. Currently awaiting more magnets for the second boot (used most of them for the first one), trying different magnet orientations, and searching for a spot to test them upside down.

Stay tuned, will have them up and running, er, well, hanging, soon!

Many thanks to: Tinker Tank at Pacific Science Center for being my build and test center, and to Richard Albritton for the CNC help!

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.