In Assignment 1, you learned how to get data from the Internet and visualize it. In this assignment, you’ll use your newfound Javascript skills to interact with your Photon; you’ll also learn a bit of microcontroller programming in C.


The main goal for this assignment is to get comfortable with the idea and process of sending data back and forth from a physical object (the Photon) to a computer. You’ll do this via USB and/or the Particle cloud.

The learning goals for this assignment are as follows:

  • Learn how to connect external components to your Photon;
  • connect your Photon to your computer for two-way communication over USB or the cloud;
  • learn basic C skills;
  • and become more experienced with Javascript.


This assignment counts for 33% towards your final grade. It also includes an extra 5% credit towards your final grade if you do really great. The grading for this assignment will be in two parts. First 25% of the assignment (or 8.25% of your final grade) is based on you showing up in class with the things requested in Important dates below. The remaining 90% is assigned based on your completed work, under **Evaluation##1.

Important dates

For this assignment, we’ll have several quick check-in points to help you know what to do when. Each one will be due in class, and we will troubleshoot problems. The procedure will be:

  1. Everyone will show me what they have and very briefly bring up about any problems they ran into.
  2. After everyone has talked, we will troubleshoot common and simple problems.
  3. Then we’ll go on to trickier problems.
  4. If there is time, we’ll talk about the milestone for next time. If not, you need to be independent and be prepared anyway.

Being prepared with each of these deadlines will form part of your grade for this assignment.

Date Points Thing to do by this date
Thu 9/29 5%Pick one input and one output part from parts list
Tue 10/4 5%Design your circuit and sketch your program flow; get Chrome serial working with demo program
Thu 10/6 5%Wire up your input circuit on the breadboard and have working basic input code as illustrated by serial output via particle serial monitor
Tue 10/11Classes on Monday schedule; extra office hours during class time
Thu 10/135%Wire up output circuit on the breadboard
Tue 10/185%Working basic output code
Thu 10/2590%Rest of assignment due:
Input visualization (35%)
Output visualization (35%)
Extra I/O (15%)
Deliverables ( 5%)

What to do

You’re going to connect some extra electronics to your Photon. Have a look at the list of parts that are available to see what you can choose from. In addition, you can order extra parts if you want from Sparkfun, Adafruit or other places; note that “my parts didn’t arrive” is not a valid excuse for unfinished work, though.

Look at the Resources section below. There are a lot of useful links to help you there. Also be sure to check out the Resources on the main page.

Start now! This is a more complex assignment than the first one. I’m here to help but have limited time, so it’s in your best interest to run into problem earlier rather than later!


Pick parts

Visit the list of parts and pick one input and one output part you’d like to work with. Be sure to click on links for the parts you’re interested in and read about them, especially any connection guides associated with them. Adafruit parts often have comprehensive tutorials, and Sparkfun parts often have hookup guides. Take into account the complexity of hooking up the part, the amount of programming necessary, and whether there are extra components needed.

Note that for both input and output, I would like to see more than binary. That is, if you’re going to use a button or switch for input, you should have several, and if you’re going to use an LED for output, you should have several.

Design circuit

Plan what your circuit will look like. Draw it on paper or use Fritzing. It doesn’t have to be amazing or pretty—the idea is for you to think about what you’re going to do before you start plugging things in. If you like, draw two versions, one for the input and one for the ouput. Think about whether you will have the right number of connections on your Photon to accomplish what you want to do.

Plan program

Plan how your program will work. Sketch out the general flow of what it will do. Look up what libraries you will need and read about how they work.

Wire up and test input

Wire up the input part of your circuit on your breadboard. Double-check your connections against your plan.

Write a program for your Photon to read your input and print the data out over the serial port (use particle serial monitor to see the output once the program is running). See if it works.

Wire up and test output

Take a photo or two of your working input circuit so you can recreate it later if you accidentally break something. Wire up the output part of your circuit on your breadboard. Double-check your connections against your plan.

Write a program for your Photon to generate some output. At this point, don’t try to combine it with the input program. See if it works.

Get Chrome + Serial working

You’ll need to be sure that your Photon is sending some stuff over the serial port. You can check the Particle Reference Documentation for serial ports for more information. Here is a very basic program that will print a random number to the serial port once per second, while flashing the onboard blue LED so you know the program is running:

//A #define statement is like a variable that doesn't need to change.
// I'm using it here so I can easily change which LED is flashing
// later; for example, if I hooked up an LED to D0, I could just make
// one change here.
#define LED D7

//Here I'll define how long (in ms) it should be between flashes of the LED
#define LED_FLASH_TIME 500

//And how long in between printing to the serial port
#define SERIAL_PRINT_TIME 1000

void setup()
    //Set up the Photon to talk over the USB serial port. 9600 is how
    // fast your Photon will communicate over the serial port. You don't
    // need to change it. You'll notice this value used in the Chrome
    // serial code, though.

    //Set up the LED for ouput
    pinMode(D7, OUTPUT);

    //Make sure the LED starts in the off state
    digitalWrite(LED, LOW);

//Keep track of how long it's been since we last did stuff
unsigned long timeSinceLastFlash = 0;  //How long since we flashed LED?
unsigned long timeSinceLastPrint = 0;  //How long since we last printed?

//Keep track of the current LED state
unsigned int ledState = LOW;

void loop()
    //The millis() function returns how many milliseconds since the
    // program started running. We'll use this instead of delay()
    // since delay() keeps the Photon from doing anything else.
    unsigned long now = millis();

    //If it's been more than 500ms since the last flash, we'll change
    // the LED state from off to on or from on to off.
    if(now - timeSinceLastFlash > LED_FLASH_TIME)
        //"!" means "not", so we switch the value of ledState to its
        // opposite value
        ledState = !ledState;
        digitalWrite(LED, ledState);  //Set the new state
        timeSinceLastFlash = now;     //The last change was just now

    if(now - timeSinceLastPrint > SERIAL_PRINT_TIME)
        //Print a random number between 0 and 1024 to the serial port
        Serial.print("Random number: ");
        timeSinceLastPrint = now;

Follow the instructions in Step 5 at this page to get your copy of Chrome set up for app development. Then, visit this GitHub repository and follow the instructions there to get serial port reading set up in Chrome.

Complete assignment

Now you should have the tools available to complete the assignment. Read through the Evaluation section below to find out what to do.


25% of your grade for this assignment will come from following the instructions under Important dates. Note the points for this assignment add up to 115%. This assignment is normally worth 33% of your final grade, so if you do everything to reach 115%, you’ll get 5% extra credit towards your final grade.

Input visualization (35%)

Visualize the data from your input sensor using either your visualization tool from the first assignment (adapted and possibly improved) or a new visualization method. You’ll be graded, in part, on the quality of your visualization; so if you were unhappy with how your first assignment came out, this is your chance to improve it.

Output visualization (35%)

Also display some data from the internet on your output. This can react independently to some computer- or online-based event or to the sensors attached to the Photon. In the latter case, however, the data must leave the Photon to the computer or cloud before it returns to cause a reaction. You can use any online data service such as or PubNub.

Extra I/O (15%)

Add at least one extra non-binary input and one extra non-binary output to your circuit. Make your circuit do something interesting and/or useful (beyond just simply displaying the input).

Deliverables (5%)

You’ll turn in your code via your Github repository. Along with your code, upload a file, which Github will then display with your repository. Include:

  • A description of your circuit: what sensor you used, how you are reading the data from the circuit on the Photon.
  • A description of your visualization: what libraries or techniques you used, and what differences (if any) there are from your code in the first assignment.
  • A photograph of your completed circuit, clearly showing all of the elements and their connections. Annotations would be nice but are not required.

Ensure that your images appear inline with the Readme file when you load up your repository.

You will also demo your work in class.



Are you stuck? Confused? Sad? Enraged? Please come see me! Or send me a Slack message! I would much rather spend time with you figuring out what’s going on than have you turn in something that doesn’t work.

Network problems

If you can’t get your Photon connected to the network, you can skip that part and use it unconnected. There’s more information here, but the short version is to add the line SYSTEM_MODE(SEMI_AUTOMATIC); at the top of your .ino file. This will allow your code to run right away without trying to connect to the Internet. (Obviously any cloud functions such as Spark.publish() won’t work if you use this solution!)



Learning about electronics

  1. Yes, this adds up to 115%. 100% of 33% is 33%; 15% of 33% is about 5%, which is the extra credit. I’m doing it like this, rather than assigning extra credit to a particular class, to give you more of a chance to get a good grade overall.