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In this video we are going to learn how to use interrupts with Arduino an advanced but extremely useful feature of the Arduino.. There is a lot to cover so without any further delay. Lets get started, Hello guys I am Nick and welcome to a channel that is all about DIY electronics projects with Arduino, Raspberry, Pi, ESP8266 and other popular boards. Subscribe to the channel. Now, if you dont, want miss any future video. In this video, we are going to learn how to use interrupts in our projects by building two simple projects. Be sure to watch until the end of the video, because the trick we use in the second example is Very useful for our future projects., But what is an interrupt? Most microprocessors have interrupts. Interrupts. Let you respond to external events while doing something else. Suppose you are sitting at home waiting for the new ESP32 board. You have ordered a few days ago to arrive at your mailbox.. You are very excited, so you check your mailbox every ten minutes to see if the board has arrived.. This procedure is called polling and we were using this technique a lot in our projects.. But what if we had told the mailman to ring the doorbell at his arrival? This way we are free to do anything we want and at the time the board arrives at the mailbox we get notified and we can use it at once.. This example explains exactly how an interrupt causes a processor to act.

. The Arduino program is running and performing some function.. However, when an interrupt occurs, the main program stops executing and another function is called. When this function finishes. The processor goes back to the main program again and resumes its execution from the point. It was stopped. The function that the processor executes when an interrupt happened is the ISR. The Interrupt Service Routine. Interrupts can come from various sources. In this video. We are going to learn about hardware interrupts, which are triggered by a state change on one of the digital pins.. In other words, an interrupt can be triggered when a digital pin goes from LOW to HIGH or from HIGH to LOW.. With most Arduino boards you can use only certain pins, as interrupts. Interrupts are referred to by an ID number that correspond to particular digital pin.. So interrupt 0 and an Arduino Uno corresponds to digital pin 2., The Arduino Uno, the Arduino Nano and the Arduino pro mini support. Only two external interrupts on digital pins, 2 and 3.. The Arduino Mega supports 6 external interrupts, whereas the ESP8266 chip can support 16. External interrupts. Lets now see how to use an interrupt on a digital pin of the Arduino. With an example.. We are going to use an Arduino Nano which is actually a small Arduino Uno.. You can use an Arduino Uno if you wish the code and the connections are exactly the same.. In this first example, we are going to build a simple project in which each time we press the button, an interrupt will be triggered and the ISR will change the state of the LED.

. I have connected the LED to digital pin 13 and the button to digital pin 2, which supports hardware interrupts. In order to make a digital pin to interrupt the main Arduino sketch we use the attachInterrupt function.. The first argument is the interrupt ID, so if we are using an Arduino Uno, the interrupt 0 corresponds to digital pin 2.. The next argument is the function that is going to be executed when the interrupt is triggered.. In other words, this is the ISR function.. In this example, we name the ISR buttonPressed.. The last argument tells the Arduino what triggers the interrupt. RISING means that an interrupt will be triggered when the state of Digital Pin 2 goes from LOW to HIGH.. We can also use the word FALLING, which means that an interrupt will be triggered when the state of the pin goes from HIGH to LOW.. Another option is to use the word CHANGE, which will trigger an interrupt whenever a change in the state of the pin occurs.. Now that we have enabled the interrupt we need to create the ISR., We can name the ISR buttonPressed.. The function. Checks turns the LED ON or OFF depending its state.. In order to remember the LED state, it uses a Boolean global variable., Each variable the ISR function uses must be declared as volatile.. There are some things to have in mind when you are writing an Interrupt Service Routine. Keep it short. This is very important.

Dont use delay. Dont do serial prints, Make variables shared with the main code volatile, So we have created a very short function. We dont use any delays or Serial prints and we have declared the variable as volatile.. We are ready to test the code.. As you can see, the code of the project works as expected.. When I press the button an interrupt is triggered and the LED goes on or OFF.. Our first sketch that uses interrupts is ready. If we check the code once more, we can see that the loop function is empty. We have a working project with no code in the loop function.. If we wanted to build the same project without interrupts, we would check the state of the button many times per second, in order to detect any change to its state and the turn the LED on or OFF.. This is how we were doing things so. Far. Now lets move on to the second project.. In this project. I am using a PIR sensor to trigger an interrupt.. The PIR sensor works like this.. It has only three pin Vcc GND and the signal out pin. When the sensor detects movement. The signal pin goes from LOW to HIGH and stays on for 10 seconds. If it does not detect any movement in that 10sec period. It goes back to LOW.. In this example, we want to use, interrupts to turn the LED on when a movement is detected and turn it OFF again.

When the sensor signal goes LOW., We are going to use two interrupts.. We are going to interrupt once when the state of the signal from the sensor goes from LOW to HIGH in order to turn the LED on and we are going to use another interrupt to turn the LED OFF when the signal from the sensor goes from HIGH To LOW. We connect Vcc of the sensor to 5V GND to GND, and the signal pin to digital pin 2 and digital pin 3.. Both these pins use hardware interrupts. Now in the code, the first interrupt will trigger when the signal goes from LOW to HIGH. So we use the RISING word.. When that happens, the turnLEDOn ISR function will be called.. The second interrupt has the id 1, which corresponds to digital pin 3.. We will use the FALLING word as a trigger and it will call the turnLEDOff function when triggered. The ISRoutines are very simple and short.. We just turn the LED on or off. Thats it.. The project is ready., We add a command to the loop function in order to put Arduino to sleep to conserve power., We are using the LowPower library to achieve that.. This command will put Arduino to sleep forever.. The interrupts can wake up the Arduino, execute the ISR function and get back to sleep at once.. So in this example, the Arduino is sleeping all the time when it detects motion an interrupt is triggered so the Arduino wakes up and executes the turnLEDOn function.

When this function has completed its execution. The Arduino goes back to sleep at once When the signal from the sensor goes from HIGH to LOW another. Interrupt is triggered. The ISR function of this interrupts turns the LED off and the Arduino goes back to sleep.. This is great. We dont waste any time at all. Lets test the project to see if everything works as expected. The Arduino is now sleeping and PIR sensor has not detected any movement.. If I place my hand close to the sensor, the sensor will trigger an interrupt and the Interrupt Service routine, for the first interrupt will turn the LED ON and the Arduino will get back to sleep.. If we wait for 10 seconds without moving in front of the sensor, the output of the sensor will go LOW.. The Arduino is going to wake up again in order to execute the second interrupt service routine, which will turn the LED OFF. After the LED is turned OFF. The Arduino goes back to sleep.. As you can see, we can greatly reduce the power consumption of our projects with the use of interrupts. This trick is very useful and I am going to use it a lot in the future to reduce the power consumption of our projects and extend their battery life.. As always, you can find the code of both projects in the description of the video below. Thats it.. Now that we have built some simple projects that use interrupts, we can use this very useful feature to more advanced projects.

. This will allow us to build more complex projects that use less energy. This video was quick demonstration of how to use hardware interrupts with Arduino.. There are many more things to discuss about interrupts, but what we learned today is what we are going to use the most.. I would love to hear your thoughts on interrupts.. Are you going to use interrupts in any of your projects now that you know how they work? Please, post your comments below and dont forget to like the video. If you find useful., Also consider subscribing to the channel and do click that bell or YouTube might not show you updates, as new videos come out. If you are going to be shopping for parts check out the affiliate links from the video description. Thats it for today.


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Originally posted 2016-05-23 21:22:21.

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Comment (20)

  1. My IDE is missing the lowpower.h–how can you add this to Arduino’s libraries? Found it, but this still will not compile. I installed Arduino IDE 1.8.8 and still can’t compile this As I find stm32lowpower and stm32rtc it still complains. I would really like to try this if someone can point me to the way to compile this?

  2. Nice video I could have done with it 30 years ago when I learned Assembler coding and then swapped to C cross compiler.But this was most informative for the nubbie. Helped me for the Arduino which is a nice IDE.

  3. Hi!
    I just finished the translation to Serbian.
    But, I am looking to the code No.2 and something is confusing me.
    When the arduino jump into the loop() is he execute the command to go to sleep only once and stays there until the interrupt function wake him?
    Or the loop() function will trigger another internal interrupt, wake him to execute the sleep function, send him to sleep, then wake him again to execute the sleep command, send him to sleep … ?

  4. Just a little notice at the end part that you could have only used one interrupt on CHANGE mode and if the state of the interrupt pin is high, turn it on. If low, turn it off. It’s a good idea to try and save the use of interrupt pins as much as possible, especially on an Uno.

  5. Excellent explanation, thnx!
    I’m wrestling this interrupt stuff for two weeks now, so I hope your basic setup will do the trick finally!

    1. After reading this (
      Often it is useful to steer an input pin to a known state if no input is present. This can be done by adding a pullup resistor (to +5V), or a pulldown resistor (resistor to ground) on the input. A 10K resistor is a good value for a pullup or pulldown resistor.
      I attached a 1K restistor from sensor to GND which gave an accurate result.


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