What are interrupts in Arduino, and how are they used?

Hey there!
Interrupts can seem a bit tricky at first, but once you get the hang of them, they're a game-changer for many Arduino projects.

I will explain this using a real-life example.

So, what are interrupts in simple terms?
Imagine you're in the kitchen, diligently following a recipe to bake a cake. Your loop() function is carefully measuring flour, mixing ingredients, and so on. Now, what if the doorbell rings?

Without interrupts (the loop() way): You'd have to finish a major step in your recipe (like mixing the batter) and then quickly run to the door to check if anyone is there. If your recipe step takes a long time, your visitor might get impatient and leave. This is called polling – repeatedly checking the state of something.

With interrupts: The moment the doorbell rings, you'd immediately pause what you're doing (even if you're mid-stir), answer the door, and then come back to your recipe right where you left off. The doorbell interrupted your cake-making.

Interrupts in Arduino

In Arduino, an "interrupt" is a signal to the microcontroller that an important event has occurred. When this happens, the Arduino immediately pauses its main program (loop()) to run a special, short function called an Interrupt Service Routine (ISR). Once the ISR is finished, the Arduino resumes the loop() from the exact point it was interrupted.

You're building a home automation system... should you use interrupts for a button press?
Absolutely! This is a classic and perfect use case for interrupts.

To answer your question directly: Yes, using an interrupt for a button press will make your home automation system significantly more responsive.

Think about your code. The loop() in a home automation system might be doing a lot of things:

1. Checking temperature sensors.

2. Sending data to a display.

3. Blinking status LEDs.

4. Maybe even running a small web server.

If you're just checking the button state in your main loop (digitalRead(buttonPin)), there's a chance the button is pressed and released while the Arduino is busy with another task. It would completely miss the button press!

By using an interrupt on the button pin, the Arduino will instantly detect the press, no matter what it's doing in the loop(). This ensures that your lights or fans turn on the very moment you press the button, giving your project that snappy, professional feel.

When are interrupts absolutely essential?
Here's a scenario where just checking in the loop() would likely fail:

Imagine you want to measure the speed of a spinning fan or a wheel on a robot. A common way to do this is to attach a small magnet to the fan blade and use a Hall effect sensor. Each time the magnet passes the sensor, the sensor's output pin briefly changes state.

These pulses can be very, very fast – much faster than your loop() can reliably check for. If your loop() is doing anything else that takes even a few milliseconds, you're almost guaranteed to miss pulses, leading to completely wrong speed readings.

In this case, an interrupt is essential. You would attach an interrupt to the sensor pin. The ISR for this interrupt would be super simple and fast, something like pulseCount++;. The main loop() can then use the pulseCount value to calculate the RPM whenever it needs to, without ever worrying about missing a pulse.

I hope this makes sense. You can find a lot of tutorials online on how to use Interrupts. 
But if you want, I can share an example here as well.