how to use esp32 gpio interrupts
Learn how to use ESP32 gpio interrupts using Arduino IDE. We will explain the example of an interrupt with a button and LED.
Table of Content
Why interrupts are important ?
Let’s look at a straightforward example. Imagine you have an ESP32 controlling an LED that blinks every second. At the same time, you want to press a button and display a button-pressed case on a serial monitor. Without interrupts, the ESP32 uses a loop like this:
const int ledPin = 2;
const int buttonPin = 12;
void setup() {
pinMode(ledPin, OUTPUT);
pinMode(buttonPin, INPUT_PULLUP);
Serial.begin(115200);
}
void loop() {
digitalWrite(ledPin, HIGH);
delay(1000);
digitalWrite(ledPin, LOW);
delay(1000);
if (digitalRead(buttonPin) == LOW) {
Serial.println("Button Pressed!");
} else {
Serial.println("Button Not Pressed.");
}
}
The issue with the above method is that the button pressed is not detected every time. If the button is pressed in the two-second delay time it will go unnoticed as the processor is focused on performing the other task, in this case blinking the LED.
Similarly, take the example of your laptop. If the system didn’t use interrupts, connecting a USB mouse wouldn’t trigger an immediate response. The sound you hear when connecting a USB device is a result of an interrupt. Interrupts allow the processor to respond to external events without delay, making systems more efficient and responsive.
attachInterrupt()
In arduino IDe the attachinterrupt() function is used to set interrupt on gpio pins.
Syntax:
attachInterrupt(digitalPinToInterrupt(gpiopin), ISR, mode); gpiopin – to set a particular gpio pin number as an external interrupt.
ISR (Interrupt Service Routine) – this is the function to be called when interrupt is detected. The function shouldn’t take any argument nor return any parameter.
Mode – This is the type of event that will trigger the interrupt. There are five predefined types of events:
| Low | Triggers the interrupt when LOW is detected |
| high | Triggers the interrupt when high is detected |
| Rising | Triggers the interrupt when the value (voltage) on the pin is changed from LOW to high |
| Falling | Triggers the interrupt when the value (voltage) on the pin is changed from high to LOW |
| Change | Triggers the interrupt when the value (voltage) on the pin is changed, either from high to LOW or low to high |
Code
void setup()
{
Serial.begin(115200);
delay(1000);
}
void loop()
{
Serial.println(touchRead(T0));
delay(100);
}example
const int ledPin = 2;
const int touchPin = T0;
const int touchThresold = 40;
void setup()
{
Serial.begin(115200);
pinMode(ledPin, OUTPUT);
delay(1000);
}
void loop()
{
int touchVal = touchRead(T0));
if (touchValue < touchThresold ){
digitalWrite(ledPin, HIGH); // Turn LED on
}
else{
digitalWrite(ledPin, LOW); // Turn LED off
}
delay(100);
}The code reads the input from the touch-pin T0 (GPIO4) and turns on the Led if the touch is detected.