![\"Interrupts](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/08\/ESP8266-Interrupts.jpg?resize=1200%2C675&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nAs an example, we\u2019ll detect motion using a PIR motion sensor: when motion is detected, the ESP8266 starts a timer and turns an LED on for a predefined number of seconds. When the timer finishes counting down, the LED automatically turns off.<\/p>\n\n\n\n
To create an interrupt, call attachInterrupt()<\/span> and pass as arguments the GPIO interrupt pin, the ISR (funcion to be called) and mode. The ISR function must have the ICACHE_RAM_ATTR<\/span> attribute declared. The mode can be CHANGE<\/span>, RISING<\/span> or FALLING<\/span>.<\/p>\n\n\n\n Before proceeding with this tutorial you should have the ESP8266 add-on installed in your Arduino IDE. Follow this tutorial to Install ESP8266 in Arduino IDE<\/a>, if you haven’t already.<\/p>\n\n\n\n Interrupts are useful for making things happen automatically in microcontroller programs and can help solve timing problems. <\/p>\n\n\n\n With interrupts you don\u2019t need to constantly check the current pin value. When a change is detected, an event is triggered – a function is called. This function is called interrupt service routine (ISR).<\/p>\n\n\n\n When an interrupt happens, the processor stops the execution of the main program to execute a task, and then gets back to the main program as shown in the figure below.<\/p>\n\n\n\n This is especially useful to trigger an action whenever motion is detected or whenever a pushbutton is pressed without the need to constantly check its state.<\/p>\n\n\n\n To set an interrupt in the Arduino IDE, you use the attachInterrupt()<\/span> function, that accepts as arguments: the GPIO interrupt pin, the name of the function to be executed, and mode:<\/p>\n\n\n\n The first argument is a GPIO interrupt. You should use digitalPinToInterrupt(GPIO)<\/span> to set the actual GPIO as an interrupt pin. For example, if you want to use GPIO 14 as an interrupt, use:<\/p>\n\n\n\n The ESP8266 supports interrupts in any GPIO, except GPIO16.<\/p>\n\n\n\n The second argument of the attachInterrupt()<\/span> function is the name of the function that will be called every time the interrupt is triggered \u2013 the interrupt service routine (ISR).<\/p>\n\n\n\n The ISR function should be as simple as possible, so the processor gets back to the execution of the main program quickly. <\/p>\n\n\n\n The best approach is to signal the main code that the interrupt has happened by using a global variable and within the loop()<\/span> check and clear that flag, and execute code.<\/p>\n\n\n\n ISRs need to have ICACHE_RAM_ATTR<\/span> before the function definition to run the interrupt code in RAM.<\/p>\n\n\n\n The third argument is the mode and there are 3 different modes:<\/p>\n\n\n\n For our example, will be using the RISING mode, because when the PIR motion sensor detects motion, the GPIO it is connected to goes from LOW to HIGH.<\/p>\n\n\n\n For this tutorial, we’ll use timers. We want the LED to stay on for a predetermined number of seconds after motion is detected. Instead of using a delay()<\/span> function that blocks your code and doesn\u2019t allow you to do anything else for a determined number of seconds, we\u2019ll use a timer.<\/p>\n\n\n\n The delay()<\/span> function accepts a single int number as an argument. This number represents the time in milliseconds the program has to wait until moving on to the next line of code.<\/p>\n\n\n\n When you call delay(1000)<\/span> your program stops on that line for 1 second. delay()<\/span> is a blocking function. Blocking functions prevent a program from doing anything else until that particular task is completed. If you need multiple tasks to occur at the same time, you cannot use delay()<\/span>. For most projects you should avoid using delays and use timers instead.<\/p>\n\n\n\n Using a function called millis()<\/span> you can return the number of milliseconds that have passed since the program first started.<\/p>\n\n\n\n Why is that function useful? Because by using some math, you can easily verify how much time has passed without blocking your code.<\/p>\n\n\n\n If you’re not familiar with millis()<\/span> function, we recommend reading this section. If you’re already familiar with timers, you can skip to the PIR motion sensor project.<\/p>\n\n\n\n The following snippet of code shows how you can use the millis()<\/span> function to create a blink project. It turns an LED on for 1000 milliseconds, and then turns it off.<\/p>\n\n\n View raw code<\/a><\/p>\n\n\n\n Let\u2019s take a closer look at this blink sketch that works without the delay()<\/span> function (it uses the millis()<\/span> function instead).<\/p>\n\n\n\n Basically, this code subtracts the previous recorded time (previousMillis<\/span>) from the current time (currentMillis<\/span>). If the remainder is greater than the interval (in this case, 1000 milliseconds), the program updates the previousMillis<\/span> variable to the current time, and either turns the LED on or off.<\/p>\n\n\n\n Because this snippet is non-blocking, any code that\u2019s located outside of that first if statement should work normally.<\/p>\n\n\n\n You should now be able to understand that you can add other tasks to your loop()<\/span> function and your code will still be blinking the LED every one second.<\/p>\n\n\n\n You can upload this code to your ESP8266 to test it. The on-board LED should be blinking every second.<\/p>\n\n\n\n In this section, you’ll learn how to detect motion with a PIR motion sensor using interrupts and timers in your code.<\/p>\n\n\n\n Here’s a list of the parts required to complete this tutorial:<\/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> Assemble the PIR motion sensor and an LED to your ESP8266. We\u2019ll connect the LED to GPIO 12<\/span> (D6) and the PIR motion sensor data pin to GPIO 14<\/span> (D5).<\/p>\n\n\n\n Recommended reading:<\/strong> ESP8266 Pinout Reference Guide<\/a><\/p>\n\n\n\n Important: <\/strong> the Mini AM312 PIR Motion Sensor used in this project operates at 3.3V. However, if you\u2019re using another PIR motion sensor like the HC-SR501, it operates at 5V. You can either modify it to operate at 3.3V or simply power it using the Vin pin.<\/p>\n\n\n\n The following figure shows the AM312 PIR motion sensor pinout.<\/p>\n\n\n\n After wiring the circuit as shown in the schematic diagram, copy the code provided to your Arduino IDE.<\/p>\n\n\n\n You can upload the code as it is, or you can modify the number of seconds the LED is lit after detecting motion. Simply change the timeSeconds<\/span> variable with the number of seconds you want.<\/p>\n\n\n View raw code<\/a><\/p>\n\n\n\n Let\u2019s take a look at the code.<\/p>\n\n\n\n Start by assigning two GPIO pins to the led<\/span> and motionSensor<\/span> variables.<\/p>\n\n\n\n Then, create variables that will allow you set a timer to turn the LED off after motion is detected.<\/p>\n\n\n\n The now<\/span> variable holds the current time. The lastTrigger<\/span> variable holds the time when the PIR sensor detects motion. The startTimer<\/span> is a boolean variable that starts the timer when motion is detected.<\/p>\n\n\n\n In the setup()<\/span>, start by initializing the serial port at 115200 baud rate.<\/p>\n\n\n\n Set the PIR Motion sensor as an INPUT_PULLUP<\/span>.<\/p>\n\n\n\n To set the PIR sensor pin as an interrupt, use the attachInterrupt()<\/span> function as described earlier.<\/p>\n\n\n\n The pin that will detect motion is GPIO 14<\/span> and it will call the function detectsMovement()<\/span> on RISING<\/span> mode.<\/p>\n\n\n\n The LED is an OUTPUT<\/span> whose state starts at LOW<\/span>.<\/p>\n\n\n\n The loop()<\/span> function is constantly running over and over again. In every loop, the now<\/span> variable is updated with the current time.<\/p>\n\n\n\n Nothing else is done in the loop()<\/span>. But, when motion is detected, the detectsMovement()<\/span> function is called because we\u2019ve set an interrupt previously in the setup()<\/span>. <\/p>\n\n\n\n The detectsMovement()<\/span> function prints a message in the Serial Monitor, turns the LED on, sets the startTimer<\/span> boolean variable to true and updates the lastTrigger<\/span> variable with the current time.<\/p>\n\n\n\n After this step, the code goes back to the loop()<\/span>. This time, the startTimer<\/span> variable is true. So, when the time defined in seconds has passed (since motion was detected), the following if statement will be true.<\/p>\n\n\n\n The \u201cMotion stopped\u2026\u201d message will be printed in the Serial Monitor, the LED is turned off, and the startTimer<\/span> variable is set to false.<\/p>\n\n\n\n Upload the code to your ESP8266. Make sure you have the\nright board and COM port selected.<\/p>\n\n\n\n Open the Serial Monitor at a baud rate of 115200.<\/p>\n\n\n\n Move your hand in front of the PIR sensor. The LED should turn on, and a message is printed in the Serial Monitor saying \u201cMOTION DETECTED!!!<\/strong>\u201d. After 10 seconds the LED should turn off.<\/p>\n\n\n\n To sum up, interrupts are useful to detect a change in a GPIO state and instantly trigger a function. You’ve also learned that you should use timers to write non-blocking code.<\/p>\n\n\n\n We hope you’ve found this tutorial useful. We have other tutorials on how to handle interrupts using MicroPython and using ESP32:<\/p>\n\n\n\n Learn more about the ESP8266 board with our resources:<\/p>\n\n\n\n Thanks for reading.<\/p>\n","protected":false},"excerpt":{"rendered":" In this guide, you’ll learn how to use interrupts and timers with the ESP8266 NodeMCU using Arduino IDE. Interrupts allow you to detect changes in the GPIO state without the … <\/p>\nattachInterrupt(digitalPinToInterrupt(GPIO), ISR, mode);<\/code><\/pre>\n\n\n\nIntroducing ESP8266 Interrupts<\/h2>\n\n\n\n
![\"Introducing](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/03\/interrupt.png?resize=992%2C291&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nattachInterrupt() Function<\/h2>\n\n\n\n
attachInterrupt(digitalPinToInterrupt(GPIO), ISR, mode);<\/code><\/pre>\n\n\n\nGPIO interrupt pin<\/h3>\n\n\n\n
digitalPinToInterrupt(14)<\/code><\/pre>\n\n\n\nISR<\/h3>\n\n\n\n
Interrupt modes<\/h3>\n\n\n\n
Introducing ESP8266 Timers<\/h2>\n\n\n\n
![\"Introducing](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/07\/alarm-clock-1-150x150.png?resize=150%2C150&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\ndelay() vs millis()<\/h3>\n\n\n\n
delay(time in milliseconds);<\/code><\/pre>\n\n\n\nmillis();<\/code><\/pre>\n\n\n\nBlinking an LED using millis() (without delay)<\/h3>\n\n\n\n
\/*********\n Rui Santos\n Complete project details at http:\/\/randomnerdtutorials.com \n*********\/\n\n\/\/ constants won't change. Used here to set a pin number :\nconst int ledPin = 26; \/\/ the number of the LED pin\n\n\/\/ Variables will change :\nint ledState = LOW; \/\/ ledState used to set the LED\n\n\/\/ Generally, you should use "unsigned long" for variables that hold time\n\/\/ The value will quickly become too large for an int to store\nunsigned long previousMillis = 0; \/\/ will store last time LED was updated\n\n\/\/ constants won't change :\nconst long interval = 1000; \/\/ interval at which to blink (milliseconds)\n\nvoid setup() {\n \/\/ set the digital pin as output:\n pinMode(ledPin, OUTPUT);\n}\n\nvoid loop() {\n \/\/ here is where you'd put code that needs to be running all the time.\n\n \/\/ check to see if it's time to blink the LED; that is, if the\n \/\/ difference between the current time and last time you blinked\n \/\/ the LED is bigger than the interval at which you want to\n \/\/ blink the LED.\n unsigned long currentMillis = millis();\n\n if (currentMillis - previousMillis >= interval) {\n \/\/ save the last time you blinked the LED\n previousMillis = currentMillis;\n\n \/\/ if the LED is off turn it on and vice-versa:\n if (ledState == LOW) {\n ledState = HIGH;\n } else {\n ledState = LOW;\n }\n\n \/\/ set the LED with the ledState of the variable:\n digitalWrite(ledPin, ledState);\n }\n}\n<\/code><\/pre>\n\tHow the code works<\/h4>\n\n\n\n
if (currentMillis - previousMillis >= interval) {\n \/\/ save the last time you blinked the LED\n previousMillis = currentMillis;\n (...)<\/code><\/pre>\n\n\n\n![\"ESP8266](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/08\/ESP8266-blinking-LED.jpg?resize=750%2C421&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nESP8266 NodeMCU with PIR Motion Sensor<\/h2>\n\n\n\n
Parts Required<\/h3>\n\n\n\n
![](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2017\/10\/header-200.png?w=1200&quality=100&strip=all&ssl=1\")
<\/a><\/p>\n\n\n\nSchematic Diagram<\/h3>\n\n\n\n
![\"ESP8266](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/07\/esp8266_interrupts_pir_sensor_bb.png?resize=465%2C862&quality=100&strip=all&ssl=1\")
<\/a><\/figure><\/div>\n\n\n\n![\"AM312](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/08\/mini-pir-pinout.jpg?resize=750%2C292&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nCode<\/h3>\n\n\n\n
\/*********\n Rui Santos\n Complete project details at https:\/\/randomnerdtutorials.com \n*********\/\n\n#define timeSeconds 10\n\n\/\/ Set GPIOs for LED and PIR Motion Sensor\nconst int led = 12;\nconst int motionSensor = 14;\n\n\/\/ Timer: Auxiliary variables\nunsigned long now = millis();\nunsigned long lastTrigger = 0;\nboolean startTimer = false;\n\n\/\/ Checks if motion was detected, sets LED HIGH and starts a timer\nICACHE_RAM_ATTR void detectsMovement() {\n Serial.println("MOTION DETECTED!!!");\n digitalWrite(led, HIGH);\n startTimer = true;\n lastTrigger = millis();\n}\n\nvoid setup() {\n \/\/ Serial port for debugging purposes\n Serial.begin(115200);\n \n \/\/ PIR Motion Sensor mode INPUT_PULLUP\n pinMode(motionSensor, INPUT_PULLUP);\n \/\/ Set motionSensor pin as interrupt, assign interrupt function and set RISING mode\n attachInterrupt(digitalPinToInterrupt(motionSensor), detectsMovement, RISING);\n\n \/\/ Set LED to LOW\n pinMode(led, OUTPUT);\n digitalWrite(led, LOW);\n}\n\nvoid loop() {\n \/\/ Current time\n now = millis();\n \/\/ Turn off the LED after the number of seconds defined in the timeSeconds variable\n if(startTimer && (now - lastTrigger > (timeSeconds*1000))) {\n Serial.println("Motion stopped...");\n digitalWrite(led, LOW);\n startTimer = false;\n }\n}\n<\/code><\/pre>\n\tHow the Code Works<\/h4>\n\n\n\n
const int led = 12;\nconst int motionSensor = 14;<\/code><\/pre>\n\n\n\nunsigned long now = millis();\nunsigned long lastTrigger = 0;\nboolean startTimer = false;<\/code><\/pre>\n\n\n\nsetup()<\/h4>\n\n\n\n
Serial.begin(115200);<\/code><\/pre>\n\n\n\npinMode(motionSensor, INPUT_PULLUP);<\/code><\/pre>\n\n\n\nattachInterrupt(digitalPinToInterrupt(motionSensor), detectsMovement, RISING);<\/code><\/pre>\n\n\n\npinMode(led, OUTPUT);\ndigitalWrite(led, LOW);<\/code><\/pre>\n\n\n\nloop()<\/h4>\n\n\n\n
now = millis();<\/code><\/pre>\n\n\n\nICACHE_RAM_ATTR void detectsMovement() {\n Serial.println(\"MOTION DETECTED!!!\");\n digitalWrite(led, HIGH);\n startTimer = true;\n lastTrigger = millis();\n}<\/code><\/pre>\n\n\n\nif(startTimer && (now - lastTrigger > (timeSeconds*1000))) {\n Serial.println(\"Motion stopped\u2026\");\n digitalWrite(led, LOW);\n startTimer = false;\n}<\/code><\/pre>\n\n\n\nDemonstration<\/h2>\n\n\n\n
![\"Arduino](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/02\/serial-monitor.png?resize=745%2C109&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\n![\"Interrupts](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/08\/esp8266-pir-motion-sensor.jpg?resize=750%2C421&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nWrapping Up<\/h2>\n\n\n\n