35 votes
Accepted

How do interrupts work on the Arduino Uno and similar boards?

TL;DR : When writing an Interrupt Service Routine (ISR): Keep it short Don't use delay () Don't do serial prints Make variables shared with the main code volatile Variables shared with main code may ...
  • 35.7k
19 votes
Accepted

Using millis() and micros() inside an interrupt routine

The other answers are very good, but I want to elaborate on how micros() works. It always reads the current hardware timer (possibly TCNT0) which is constantly being updated by the hardware (in fact, ...
  • 35.7k
18 votes

How many interrupt pins can an Uno handle?

There are two types of "pin change" type interrupts. The external interrupts, of which there are two on the Uno. They are called 0 and 1, however they refer to digital pins 2 and 3 on the board. These ...
  • 35.7k
14 votes

Why the need to use the volatile keyword on global variables when handling interrupts in Arduino?

First, it's volatile not Volatile. I cover these concepts in my page about Interrupts however to avoid giving a link-only answer I'll repeat the relevant bits. What are "volatile" variables? ...
  • 35.7k
12 votes

Attach the Arduino ISR function to the class member

Interrupt Service Routine (ISR) outside a class Let's consider a simple use of interrupts: volatile bool switchChanged; void switchPressed () { switchChanged = true; } // end of switchPressed ...
  • 35.7k
9 votes
Accepted

How to properly use volatile variables in Arduino?

You need to learn about critical sections. What is probably happening is that the variables are being changed by the interrupt routines mid-way through the calculations. Your 'fix' reduces the time ...
  • 104k
9 votes

Calling I2C functions inside an ISR

Here is an analogy for you to help you understand why using the IRQ is a good idea. Imagine you are at a conference. There's hundreds of you in the audience, and you are in a question and answer ...
  • 104k
9 votes
Accepted

What is the right way to query an I2C device from an interrupt service routine?

Just because a pin is called "interrupt" doesn't mean that you have to read it using an interrupt input. The INTx pins of the ADXL345 are simple "level" outputs. All the time there is an "interrupt" ...
  • 104k
8 votes
Accepted

What's the benefits between different interrupts on Arduino

Imagine that you have the circuit below: simulate this circuit – Schematic created using CircuitLab Let's say that you wanted to catch the user pressing the button. The input signal will go ...
  • 261
8 votes

Using millis() and micros() inside an interrupt routine

It is not wrong to use millis() or micros() within an interrupt routine. It is wrong to use them incorrectly. The main thing here is that while you are in an interrupt routine "the clock isn't ...
  • 104k
8 votes
Accepted

Sending serial data in an interrupt

You cannot use Serial inside an interrupt. Transmitting Serial relies on interrupts being available, and from inside an interrupt they aren't. All Serial communication must be done from loop(). So ...
  • 104k
7 votes

IR Receiver interrupt and arduino sleep mode

This is what I have managed to achieve ... Library IRLib - GitHub Version 1.51 March 2015 Copyright 2013-2015 by Chris Young http://tech.cyborg5.com/irlib/ This library is a major rewrite ...
  • 35.7k
7 votes

interrupting an interrupt

the timer will set the Timer Interrupt Flag (TIFR0 register) The ISR will be called, and the flag will be cleared you do some long calculations or something the timer will match OCR0A, and set the ...
  • 11.1k
6 votes

Using millis() and micros() inside an interrupt routine

The quoted phrase is not a warning, it is merely a statement about how things work. There's nothing intrinsically wrong with using millis() or micros() within a properly-written interrupt routine. ...
6 votes
Accepted

Critical sections in Arduino, interrupt consuming data

Warning: I am not familiar with the ESP8266 hardware, and some of my answers below may be only valid on the AVR architecture. The simplest way to synchronize your main code with your interrupt ...
  • 39.1k
6 votes
Accepted

Using a lot of interrupts on a single Arduino

On a Uno, all of the digital and analog pins can trigger a pin-change interrupt. That gives you 20 inputs straight away. The Mega also has pin change interrupts but not on all its pins. The pins that ...
  • 35.7k
6 votes
Accepted

Arduino Interrupt example not working

I think you misunderstood this example: it is not expected to automatically blink! The LED is suposed to change state at every change of level on pin 2. This supposes that you wired something (e.g. a ...
  • 8,895
6 votes

How to generate hardware interrupt in mpu6050 to wakeup arduino from SLEEP_MODE_PWR_DOWN mode?

Well, this code worked. In this code, MPU's INT PIN is Active Low so generates Ground on motion which is than connected to INT0 or arduino UNO pin 2 which generates interrupt and wakes UP the MCU #...
  • 179
6 votes
Accepted

ATTiny13 Interrupt Issue

You would want your bool LED_STATE = false; to be volatile qualified like volatile bool LED_STATE = false; otherwise the compiler's optimizer may assume that the value cannot be changing between loads ...
  • 4,566
5 votes
Accepted

How to update a variable in an ISR using Timers

In CTC mode the top is OCR3A, not OCR3B! After that TIMSK3 |= (1 << OCIE3B); should also be changed to TIMSK3 |= (1 << OCIE3A);, and ISR(TIMER3_COMPB_vect) to ISR(TIMER3_COMPA_vect) For ...
  • 11.1k
5 votes

Interrupts for analog inputs

It is not possible to trigger an interrupt when an analog input has reached a threshold on any tinyAVR or megaAVR. It is possible to trigger an interrupt when an analog input of an AVR XMEGA with the ...
5 votes
Accepted

What happens if an interrupt is triggered while sending data via serial?

If you are on the ardruino platform, and are using the hardware serial port, you basically don't have to do anything. The Serial library interface already uses a outgoing data-buffer (it's varies ...
  • 2,584
5 votes
Accepted

Reading I2C sensors with a timer interrupt

Try putting sei(); at the start of the ISR. I think I2C needs interrupts enabled to work.
  • 11.1k
5 votes

Reading I2C sensors with a timer interrupt

I2C requires interrupts to work, however enabling interrupts inside an ISR is not recommended. For one thing you may get into a race condition, where another interrupt occurs while processing the ...
  • 35.7k
5 votes
Accepted

Where is documentation on Arduino's Internal Interrupts?

The vector names are all defined within the header files for the main chip in the compiler. The IDE doesn't need to know anything about that kind of thing - that's all up to the compiler. Look for ...
  • 104k
5 votes
Accepted

Read RC receiver channels using Interrupt instead of PulseIn

Regarding the question, “Does PinChangeInt only work on digital pins?”, note that PCI's work on all the digital pins of an ATmega328, and on the first six analog pins. (32-pin '328s have eight analog ...
5 votes
Accepted

AVR timer overflow interrupt not working

You are misunderstanding what an overflow interrupt is. That is called when the timer overflows (ie. it reaches TOP which in the case of an 8-bit timer is 255). Since you are counting to 124 that will ...
  • 35.7k
5 votes
Accepted

Managing 2 ultrasonic sensors without blocking the other

I strongly advice you to use interrupts and make sure the sensors are in a cylindrical cone in order to prevent interference to each others as much as possible. Here is code snippet which can give ...
  • 394

Only top scored, non community-wiki answers of a minimum length are eligible