Hey. I'm Jose Sanchez.

Adventures in EmbeddedSystems-land

Posted on: Wed Nov 04 2026 17:43:59 GMT+0000 (Coordinated Universal Time)

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One of the things that surprises me about the technology we use is how cheap it has become, and how (relatively) powerful it is, especially when we look at it historically. The (Apollo X) mission achieved its goal of taking people to the moon on _MB of RAM. It is because of this that I decided to enroll on an embedded systems class at DePaul. There are lots of different takeaways, but I learned quite a bit about FreeRTOS, bare-metal fundamentals, interfacing with electronics, and how to build projects.

To learn more about this, I decided to recreate an item which I'd bought already - a cheap $15 pomodoro timer on Amazon - and augment it to suit my purposes more. The item in question is here:

Choosing The Parts

Surprisingly, this is the easy part. I've studied a bit on the types of microcontrollers that are used. The STM32 series is very commonplace, especially in professional settings. NRF microcontrollers, powered by the same ARM technology that pervades our modern phones, is excellent at battery life. However, in the end I chose to use a more common, hobbyist-level microcontroller: the ESP32. It is cheap, easy-to-work, and good - albeit not great - at battery life.

One of the best parts of the above is that it is available as part of many different bundles, like this one. It includes a ton of components; we'll use the microcontroller, a tiny display (SSD1306), gyroscope (MPU6050), speaker, and of course a breadboard. This gives us a great starting point to make projects (some ideas which I might detail in later posts).

The Architecture

Let's get the basics out of the way first: this project will use PlatformIO (pio-duino) and the Arduino framework. These are tools that simplify developing for different microcontrollers, and for this project they'll work great. We'll use a mix of C and C++ for simplicity.

A project like this has a few requirements that I want it to achieve:

• Gyro controls
• The ability to have a timer
• Customizability via a web UI; this was a pain point in the Amazon-bought one
• Some sort of output (display and sound)

The nice thing is that a lot of these requirements map into specific tasks pretty well. FreeRTOS has the concept of tasks, which are functions that run concurrently. They don't always map to threads since those are not found much on microcontrollers and multithreading is expensive, and basic concurrency - scheduling code to appear like it's running at the same time - works well for these tasks. These tasks are scheduled onto FreeRTOS with xTaskCreate, and essentially run a loop that allows other tasks to run with vTaskDelay. Ultimately we get a list of 4 tasks, each of which we have to schedule so they don't have priority conflicts. We also do have to set up some interrupts as these are the recommended way to handle changes in timer value.

With these we need a bunch of ways to access data safely throughout the threads: semaphores to handle time, message queues. This is to pass event information safely to threads through the interrupts.

Lastly, we'll use a few libraries to simplify things.

• Every peripheral has its own library with methods to interact, so Adafruit_SSD1306 and Adafruit_MPU6050 are instrumental.
• ESP32-AudioI2S is a good way to add audio to our project.
• From what I googled, NVS is the way to store data
• AsyncWebServer is one way to create a simple web server.

The State Machine

One of the biggest design patterns from my embedded class (and from related videos) is the use of state machines to A) initialize peripherals and B) keep track of errors cleanly. As such, we keep track of every state:

• Initialization,
• At Work Time
• At Break Time
• Countdown Running (alterative mode)
• Timer Finished

These are declared at the top, and all tasks have to take these into account. The code ends up looking like this:

enum AppState
{
  INIT,
  IDLE,
  WORKING,
  BREAKING,
  FINISHED
};
volatile AppState globalState = AppState::INIT;
// use it elsewhere...
    AppState state = getSystemState();
    case INIT:
      break;
    case WORKING:

Ultimately, the code for tasks looks like this:

xTaskCreate(tfInteraction, "InteractionTask", 1000, NULL, 3, &tInteraction);
xTaskCreate(tfIMU, "IMUTask", 1000, NULL, 2, &tIMU);
xTaskCreate(tfNetwork, "NetworkTask", 1000, NULL, 4, &tNetwork);
xTaskCreate(tfTimer, "TimerTask", 1000, NULL, 1, &tTimer);