![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2025\/07\/ESP32-FreeRTOS-semaphores.jpg?resize=1200%2C675&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\nThere are two types of semaphores: binary semaphores <\/strong>and counting semaphores<\/strong>. In this tutorial, we’ll create and explore two different examples to show you how these two types of semaphores work.<\/p>\n\n\n\n New to FreeRTOS? <\/strong>Start with this tutorial: ESP32 with FreeRTOS (Arduino IDE)\u2014Getting Started Guide: Creating Tasks<\/a>.<\/p>\n\n\n\n Semaphores are signaling tools in FreeRTOS used to coordinate tasks. They are commonly used to indicate that an event has occurred or that a resource is available. Unlike queues, semaphores don’t carry data, only a “count” , or “flag”, or “signal” (or whatever you want to call it) used to trigger actions when something happens.<\/p>\n\n\n They allow tasks to wait for events, such as a button press or motion detection, or to signal that an event has occurred. This makes them especially useful in scenarios involving interrupts and task synchronization.<\/p>\n\n\n\n Since semaphores don\u2019t store data, they consume less memory than queues and are ideal for lightweight event signaling between tasks.<\/p>\n\n\n\n There are two types of semaphores:<\/p>\n\n\n\n Here are some basic functions of binary and counting semaphores <\/strong>when using the ESP32 with Arduino IDE. We’ll explore these functions in practical examples next.<\/p>\n\n\n\n To create a binary semaphore, use the xSemaphoreCreateBinary()<\/span> function. It returns a SemaphoreHandle_t<\/span> handle if successful, or NULL<\/span> if the creation fails.<\/p>\n\n\n\n To create a counting semaphore, use the xSemaphoreCreateCounting()<\/span> function. It returns a SemaphoreHandle_t<\/span> handle if successful, or NULL<\/span> if the creation fails. Pass as an argument the maximum count.<\/p>\n\n\n\n Use the xSemaphoreTake(semaphore, timeout)<\/span> function in a task to wait for or take a semaphore. For a binary semaphore, it blocks until the semaphore is available (state 1), setting it to 0 when taken.<\/p>\n\n\n\n For a counting semaphore, it decrements the count if greater than 0, or blocks if the count is 0. The timeout parameter specifies how long to wait (in ticks); portMAX_DELAY<\/span> means wait indefinitely. This means the task will be blocked until there’s a semaphore value to take.<\/p>\n\n\n\n To give a semaphore use the xSemaphoreGive()<\/span> function if inside a task, or xSemaphoreGiveFromISR()<\/span> if used in ISRs (interrupt service routine functions).<\/p>\n\n\n\n For a binary semaphore, it sets the state to 1, unblocking a waiting task (or ignored if the semaphore is already 1). For a counting semaphore, it increments the count up to maxCount<\/span>, unblocking a waiting task (ignored if at maxCount<\/span>).<\/p>\n\n\n\n In this section, we’ll build a simple example to demonstrate how a binary semaphore works and how to implement it in a practical application. This example will toggle an LED once when the pushbutton is pressed. To signal the button press, we’ll use a semaphore. Simultaneously, we’ll have another task blinking an LED to demonstrate that we can have multiple tasks running simultaneously.<\/p>\n\n\n So, here’s an overview of the example:<\/p>\n\n\n\n Here’s a list of the parts required for this example:<\/p>\n\n\n\n You can use the preceding links or go directly to MakerAdvisor.com\/tools<\/a> to find all the parts for your projects at the best price!<\/p>Introducing Semaphores<\/h2>\n\n\n\n
![\"Simple](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2025\/07\/binary-semaphore-how-it-works.png?resize=750%2C457&quality=100&strip=all&ssl=1\")
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Semaphores Basic Functions<\/h2>\n\n\n\n
Creating a Binary Semaphore<\/h3>\n\n\n\n
Creating a Counting Semaphore<\/h3>\n\n\n\n
Taking a Semaphore (Getting from the Semaphore)<\/h3>\n\n\n\n
Giving a Semaphore<\/h3>\n\n\n\n
Example 1: Binary Semaphore – Toggling an LED with a Button Press<\/h2>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2025\/07\/ESP32-one-pushbutton-two-LEDs.jpg?resize=750%2C422&quality=100&strip=all&ssl=1\")
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Parts Required<\/h3>\n\n\n\n
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<\/a><\/p>\n\n\n\n![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2025\/07\/ESP32-Two-LEDs-One-Pushbutton_bb.png?resize=786%2C899&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2025\/07\/ESP32-pushbutton.two-LEDs-pressing-button.jpg?resize=750%2C422&quality=100&strip=all&ssl=1\")
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