The final lab of the Spring 2025 semester introduced us to real-time operating systems (RTOS) for embedded systems. We ran a series of Arduino sketches on the ESP32S3 that demonstrate essential RTOS capabilities, such as task scheduling, memory allocation, queuing, and multicore operations. The video below demonstrates the functionality of all 7 exercises, and code screenshots for each exercise can be found after the video.

Scheduling LED blinks at different speeds without using the main 

Prioritization of tasks using non-blocking logic. 

Inter-task communication to avoid stack overflows and task conflicts. 

) to control access to shared resources (e.g., global variables) 

Run tasks on multiple cores of the ESP32 to improve efficiency

This project streams live video over WiFi and simultaneously stores static images on the SD card. I was not able to use the code provided in class, so I combined the camera timer functionality from the code provided in class with an example Arduino sketch (Examples/ESP32/Camera/CameraWebServer). 

Week 14 - Real-Time Operating System (RTOS)

This lab entailed the creation of a motor controller using pulse-width modulation (PWM) to change the speed of a DC-motor.

The circuit includes the XIAO ESP32-S3, a small DC motor, one transistor (TIP120), one diode (IN914), two push buttons, one 4.7kΩ resistor, and two 1kΩ resistors (for the buttons). We also used the XIAO expansion board, which allowed us to power the motor using a dedicated LiPo battery, rather than powering it directly from the microcontroller. Our challenge was to use the push buttons to change the motor speed by adjusting the motor's duty cycle via PWM. 

The defining feature of our code was the use of interrupts to handle changes in fan speed. The interrupt routines were instantiated in the 

 function, and allowed us to control the fan speed asynchronously in response to hardware button presses. 

We had some issues getting the circuit to respond to button presses consistently, and the oscilloscope in the video shows quite a bit of noise in the circuit. This may have been due to defective buttons or loose jumper cables, but you can see the basic functionality of the system in the video below. 

The code used for our demo can be downloaded 

Week 13 - Motor Controller 

During the Week 2 lab, we used example sketches to access the sensors and peripherals on the 

. The results of my collaboration with fellow student, Linto Thomas, are below.

We first collected accelerometer, gyroscope, and temperature data from the built-in IMU and printed it to the serial monitor.

We also accessed the microphone and used the serial plotter to visualize the signal.

In this exercise, we used the example sketch to printing text on the OLED display. I slightly modified the example sketch by adding a line to display my name, which is visible in the images below. 

The sketch below writes data to the SD card. We experienced some inconsistencies when trying to view the 

 file written to the SD card, but were able to view the file on a Windows laptop. The output file Linto Thomas generated from this sketch can be downloaded 

The screenshot below shows how the RTC is set. The sketch was first uploaded with the clock set to the the current time (using Central Time) during the lab. The methods for setting the time were then commented out and the board was flashed again so the time would not reset whenever the device is turned on.

This sketch plays the "Happy Birthday" song using the buzzer. The melody is audible in the video below.

This sketch (right) enables Bluetooth connections to the board. Line 42 of the code was changed to 

 so I could locate the board amongst the many other BLE devices in the lab. The mobile screenshot (right) shows the successful connection, which is also visible in the Arduino IDE serial monitor. 

. I use a similar setup for my personal website. While the initial configuration is somewhat complex, it is otherwise simple to customize the website and create new posts in a consistent format.

James Cole

Week 2 - Sensors and connectivity

Introduction

0. Built-in IMU and Microphone

1. OLED Display

2. MicroSD Card

3. RTC (Real-time clock)

4. Buzzer

5. Bluetooth Low Energy

Other updates

More posts

Week 14 - Real-Time Operating System (RTOS)

Week 13 - Motor Controller