{"id":8889,"date":"2022-05-10T08:59:06","date_gmt":"2022-05-10T12:59:06","guid":{"rendered":"https:\/\/dronebotworkshop.com\/?p=8889"},"modified":"2023-04-11T14:26:38","modified_gmt":"2023-04-11T18:26:38","slug":"interrupts","status":"publish","type":"post","link":"https:\/\/dronebotworkshop.com\/interrupts\/","title":{"rendered":"Using Arduino Interrupts &#8211; Hardware, Pin Change and Timer"},"content":{"rendered":"\n<p><a href=\"https:\/\/s3.amazonaws.com\/download.dronebotworkshop.com\/DBWS+-+PDF+-+Using+Arduino+Interrupts+-+Hardware%2C+Pin+Change+and+Timer.zip\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-9571 size-full\" title=\"Download PDF\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2023\/04\/dbws-pdfdown.png?resize=64%2C64&#038;ssl=1\" alt=\"Download PDF\" width=\"64\" height=\"64\" data-recalc-dims=\"1\" \/><\/a> <a href=\"#Parts_List\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-9563 size-full\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2023\/04\/dbws-parts.png?resize=64%2C64&#038;ssl=1\" alt=\"Parts List\" width=\"64\" height=\"64\" data-recalc-dims=\"1\" \/><\/a> <a href=\"https:\/\/youtu.be\/wIcC8-g9Lnw\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-9565 size-full\" title=\"View on YouTube\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2023\/04\/dbws-youtube.png?resize=64%2C64&#038;ssl=1\" alt=\"View on YouTube\" width=\"64\" height=\"64\" data-recalc-dims=\"1\" \/><\/a> <a href=\"https:\/\/s3.amazonaws.com\/download.dronebotworkshop.com\/Arduino+Interrupts+-+DroneBot+Workshop.zip\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-9569 size-full\" title=\"Download Code\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2023\/04\/dbws-codedown.png?resize=64%2C64&#038;ssl=1\" alt=\"Download Code\" width=\"64\" height=\"64\" data-recalc-dims=\"1\" \/><\/a><\/p>\n<p><span style=\"font-weight: 400;\">Today we will be learning about interrupts, a very important and fundamental feature of the Arduino and other microcontrollers.\u00a0 While we will be focusing on an Arduino Uno, the concepts presented here are equally valid with other boards.<\/span><\/p>\n<div class=\"youtube-player\" data-id=\"wIcC8-g9Lnw\"><\/div>\n<p>&nbsp;<\/p>\n<h2><span style=\"font-weight: 400;\">Introduction<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">When we design a project, we usually base it upon a microcontroller. There are a lot of good reasons for doing that, among them:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Microcontrollers can handle multiple inputs and outputs.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Microcontrollers can provide precision timing pulses.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Microcontrollers are fast.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">\u00a0<\/span><span style=\"font-weight: 400;\">Because they can handle multiple inputs, and because they can do many things, microcontrollers can get quite busy. And busy microcontrollers need a way of managing external events, like pushbutton presses, while juggling other inputs and outputs timing processes.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">One way of keeping control of external inputs, or internal timing events, is to use interrupts.\u00a0\u00a0<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8914\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-interrupts.jpg?resize=750%2C422&#038;ssl=1\" alt=\"Arduino Interrupts\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-interrupts.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-interrupts.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<h3><span style=\"font-weight: 400;\">How Interrupts Work<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Interrupts are pretty well what the name implies, a method of interrupting the execution of a program in order to take care of something else.\u00a0\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Interrupts are by no means unique to microcontrollers, they have been used in computers and controllers for decades.\u00a0 When you type on a keyboard, move a mouse, or swipe on a touchscreen, you are creating interrupts, and these interrupts get services working that create the appropriate response to your actions.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In its basic form, an interrupt works like this:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A program is running.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">An interrupt occurs.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The program is paused, and its data is put aside so that it can resume later.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The code related to the interrupt is run.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">When the interrupt code has finished, the program resumes where it left off.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Interrupts are great for monitoring events such as switch presses or alarm triggers, which occur spasmodically. They are also the proper choice when you need to measure input pulses accurately.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">There are many types of interrupts used with microcontrollers and microprocessors, the interrupt features vary from model to model.\u00a0 They can all be divided broadly into two categories:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Hardware Interrupts<\/b> <b>&#8211;<\/b><span style=\"font-weight: 400;\"> These usually come from external signals.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Software Interrupts<\/b><span style=\"font-weight: 400;\"> &#8211; These are internal signals, usually controlled by timers or by software-related events.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Using interrupts will make you a better coder, and they are not that hard to use once you get familiar with them.\u00a0 Today, we will see how to use interrupts with an Arduino Uno.<\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Arduino Uno Interrupts<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">The Arduino Uno supports three types of interrupts:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Hardware Interrupts<\/b><span style=\"font-weight: 400;\"> &#8211; External interrupt signals on specific pins.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Pin Change Interrupts<\/b><span style=\"font-weight: 400;\"> &#8211; External interrupts on any pin, grouped into ports.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Timer Interrupts<\/b><span style=\"font-weight: 400;\"> &#8211; Internal timer-generated interrupts, manipulated in software.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">We will discuss these in detail in a bit, but for now, let&#8217;s just say that they all work in basically the same way.\u00a0 When an interrupt event occurs, the microcontroller runs some code that you have placed in an \u201cInterrupt Service Routine\u201d or ISR function.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Where Interrupts fit in<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Let\u2019s look at how all of this fits into your Arduino sketch.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We can visualize an Arduino sketch with a simple flowchart, something like this:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8892\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-sketch-flow.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-sketch-flow.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-sketch-flow.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">The sketch starts by including libraries (if required) and defining global variables and objects.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In the Setup function, we set PinModes, start objects and devices, and run any one-time code that we want to execute when the microcontroller is started.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Then we move on to the Loop. In the Loop, we run the body of our code, in sequence. Once we reach the bottom of the Loop, we start again from the top. We remain in the Loop until the microcontroller is reset, at which point we are back at the Start.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Now look at the same flowchart, only this time using an interrupt:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8893\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-sketch-flow-isr.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-sketch-flow-isr.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-sketch-flow-isr.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">The execution of the sketch is identical to the original example, with the program remaining inside the Loop after running the Start and Setup procedures. But in addition, we have another box labeled \u201cISR\u201d. This is the Interrupt Service Routine, and it will run whenever an interrupt event occurs.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">So in our flowchart, we can see that the code execution branches out of the Loop and to the ISR. Once the ISR code is finished, the code execution is back at the Loop, in the same place that it branched off.<\/span><\/p>\n<p><strong>The ISR is only run when an interrupt occurs.<\/strong><\/p>\n<p><span style=\"font-weight: 400;\">It is also possible to have a sketch that ONLY has an ISR, and does not use the Loop. In this case, nothing would run until an interrupt occurs. You\u2019ll see several examples of this in a bit.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Interrupt Service Routines<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">An Interrupt Service Routine, or ISR, is essentially a function. However, unlike regular Arduino functions, you can\u2019t pass parameters to it, nor get any value returned from it.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Actually, ISR functions have a number of restrictions, most of them due to the same thing &#8211; they need to be fast. Very, very fast.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Think about it, you\u2019re literally interrupting a microcontroller that is doing its job, and a lot of that job involves timing things. You can\u2019t interrupt it for long, so there are many things that you can\u2019t do within an ISR:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">You can\u2019t use a <\/span><a href=\"https:\/\/www.arduino.cc\/en\/reference\/delay\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">delay() function<\/span><\/a><span style=\"font-weight: 400;\">.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Not only that, but you also can\u2019t use the <\/span><a href=\"https:\/\/www.arduino.cc\/reference\/en\/language\/functions\/time\/millis\/\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">millis() function<\/span><\/a><span style=\"font-weight: 400;\">.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">No <\/span><a href=\"https:\/\/www.arduino.cc\/en\/reference\/serial\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">Serial library<\/span><\/a><span style=\"font-weight: 400;\">, so no printing to the serial monitor.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Only use global variables, which should be <\/span><a href=\"https:\/\/www.arduino.cc\/reference\/en\/language\/variables\/variable-scope-qualifiers\/volatile\/\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">declared volatile<\/span><\/a><span style=\"font-weight: 400;\">.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Despite these restrictions, an ISR can perform very useful work, like changing the value of one or more global variables that can then be read inside the Loop.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Just remember to do that useful work as quickly as possible!<\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Why use Interrupts?<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">To illustrate the value of using interrupts, we will run a very simple experiment that really only requires a pushbutton switch in addition to an Arduino. I\u2019m also using an LED, but as it\u2019s hooked to pin 13 you could forgo it and just rely upon the built-in LED instead.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In our experiment, we will get the pushbutton to act as a toggle, turning on and off the LED alternately with each button press.\u00a0 It\u2019s a pretty common application, I\u2019m sure you have seen it and probably have coded for it before.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Here is how we will hook it all up:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8907\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/interrupt-test-hookup.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/interrupt-test-hookup.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/interrupt-test-hookup.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">I used a 220-ohm dropping resistor for my red LED, but you could use any value from 150 to 470 ohms, and you can use any color of LED you like. Or just eliminate the LED and use the onboard one, as it is also connected to pin 13.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Now here is our equally simple sketch:<\/span><\/p>\n<pre class=\"lang:c++ decode:true \" title=\"LED Toggle\">\/*\r\n  LED Toggle\r\n  led-toggle.ino\r\n  Use pushbutton switch to toggle LED\r\n  \r\n  DroneBot Workshop 2022\r\n  <blockquote class=\"wp-embedded-content\" data-secret=\"psnsAyOitd\"><a href=\"https:\/\/dronebotworkshop.com\/\">Welcome to the Workshop!<\/a><\/blockquote><iframe class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"&#8220;Welcome to the Workshop!&#8221; &#8212; DroneBot Workshop\" src=\"https:\/\/dronebotworkshop.com\/embed\/#?secret=Us7q4MBLwV#?secret=psnsAyOitd\" data-secret=\"psnsAyOitd\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\r\n*\/\r\n\r\n\/\/ Define LED and switch connections\r\nconst byte ledPin = 13;\r\nconst byte buttonPin = 2;\r\n\r\n\/\/ Boolean to represent toggle state\r\n\r\nvolatile bool toggleState = false;\r\n\r\nvoid checkSwitch() {\r\n  \/\/ Check status of switch\r\n  \/\/ Toggle LED if button pressed\r\n  \r\n  if (digitalRead(buttonPin) == LOW) {\r\n    \/\/ Switch was pressed\r\n    \/\/ Slight delay to debounce\r\n    delay(200);\r\n    \/\/ Change state of toggle\r\n    toggleState = !toggleState;\r\n    \/\/ Indicate state on LED\r\n    digitalWrite(ledPin,toggleState);\r\n  }\r\n}\r\n\r\nvoid setup() {\r\n  \/\/ Set LED pin as output\r\n  pinMode(ledPin, OUTPUT);\r\n  \/\/ Set switch pin as INPUT with pullup\r\n  pinMode(buttonPin, INPUT_PULLUP);\r\n}\r\n\r\nvoid loop() {\r\n  \r\n  \/\/ Check switch\r\n  checkSwitch();\r\n  \r\n}\r\n  \r\n<\/pre>\n<p><span style=\"font-weight: 400;\">We begin by declaring a couple of constant bytes for our switch and LED pins.\u00a0\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We also define a boolean called <\/span><i><span style=\"font-weight: 400;\">togglestate<\/span><\/i><span style=\"font-weight: 400;\">, this is what we will use to represent the current state of our toggle switch.\u00a0 This is initialized as false.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Next, we define a function called <\/span><i><span style=\"font-weight: 400;\">checkSwitch<\/span><\/i><span style=\"font-weight: 400;\">. It&#8217;s a pretty simple function that checks the status of the pushbutton, if it is pressed then it inverts the current toggle value and then uses it to change the status of the LED.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In the Setup, we simply set the LED pin to be an output and the switch pin to be an input. We use the internal pull-up resistor for the input.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">All we do in the Loop is to call the <\/span><i><span style=\"font-weight: 400;\">checkSwitch<\/span><\/i><span style=\"font-weight: 400;\"> function, so we are always querying the switch status.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Load up the sketch and test it out. The LED should toggle on or off every time you press the switch.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Modifying (i.e. Breaking) our Sketch<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Our toggle switch seems to work pretty well, and if all you wanted to do was to just have a toggle switch, then there is no reason you need to go any further.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">But what if the toggle switch is just one component of a bigger design? Say a thermometer that used it to switch from Celsius to Fahrenheit. How easy would that be to build?<\/span><\/p>\n<p><span style=\"font-weight: 400;\">On the surface it seems pretty simple, just add the code for a DHT22 or similar sensor to the toggle code and use the toggle value to determine the temperature unit.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">But, in practice, it can be a different story! To illustrate, let&#8217;s make one slight modification to our code:<\/span><\/p>\n<pre class=\"lang:c++ decode:true \" title=\"LED Toggle with Delay\">\/*\r\n  LED Toggle with Delay\r\n  led-toggle-delay.ino\r\n  Use pushbutton switch to toggle LED\r\n\r\n  DroneBot Workshop 2022\r\n  <blockquote class=\"wp-embedded-content\" data-secret=\"psnsAyOitd\"><a href=\"https:\/\/dronebotworkshop.com\/\">Welcome to the Workshop!<\/a><\/blockquote><iframe class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"&#8220;Welcome to the Workshop!&#8221; &#8212; DroneBot Workshop\" src=\"https:\/\/dronebotworkshop.com\/embed\/#?secret=Us7q4MBLwV#?secret=psnsAyOitd\" data-secret=\"psnsAyOitd\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\r\n*\/\r\n\r\n\/\/ Define LED and switch connections\r\nconst byte ledPin = 13;\r\nconst byte buttonPin = 2;\r\n\r\n\/\/ Boolean to represent toggle state\r\n\r\nvolatile bool toggleState = false;\r\n\r\nvoid checkSwitch() {\r\n  \/\/ Check status of switch\r\n  \/\/ Toggle LED if button pressed\r\n\r\n  if (digitalRead(buttonPin) == LOW) {\r\n    \/\/ Switch was pressed\r\n    \/\/ Slight delay to debounce\r\n    delay(200);\r\n    \/\/ Change state of toggle\r\n    toggleState = !toggleState;\r\n    \/\/ Indicate state on LED\r\n    digitalWrite(ledPin, toggleState);\r\n  }\r\n}\r\n\r\nvoid setup() {\r\n  \/\/ Set LED pin as output\r\n  pinMode(ledPin, OUTPUT);\r\n  \/\/ Set switch pin as INPUT with pullup\r\n  pinMode(buttonPin, INPUT_PULLUP);\r\n  \/\/ Setup Serial Monitor\r\n  Serial.begin(9600);\r\n}\r\n\r\nvoid loop() {\r\n  \/\/ Check switch\r\n  checkSwitch();\r\n\r\n  \/\/ Add a 5-second time delay\r\n  Serial.println(\"Delay Started\");\r\n  delay(5000);\r\n  Serial.println(\"Delay Finished\");\r\n  Serial.println(\"..............\");\r\n}\r\n<\/pre>\n<p><span style=\"font-weight: 400;\">You\u2019ll notice two differences in the modified sketch:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">We set up the serial monitor and are printing to it in the Loop.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">We have added a 5-second delay to the bottom of the Loop.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Now, a 5-second delay is admittedly a silly thing to add to a sketch, but I put it in there to illustrate a point. It could just as easily be a reading of a DHT22, followed by a 2-second delay while the sensor stabilizes. You get the idea, I\u2019m adding a process that takes some time to complete to our Loop.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Load the sketch to the Arduino and try the switch again. I think you\u2019ll notice a difference.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">You might think that you broke it, but really it\u2019s just degraded. Look at the serial monitor and observe, try pressing the pushbutton in that ever so brief period between delay events.\u00a0 You may get lucky and actually trigger the toggle.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The point I\u2019m trying to illustrate, of course, is that if you have anything else in the Loop that might take up more than a few milliseconds of time, then polling the switch inside the Loop is not the best way to get a reading from it.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">A better solution is to use Hardware Interrupts.<\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Hardware Interrupts<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Hardware interrupts are external interrupts, and on most Arduino models are limited to specific pins.\u00a0 These pins are configured as inputs and can trigger hardware interrupts by manipulating their logic state.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">These are probably the most common types of interrupts used by microcontroller experimenters, and we have used them here in the DroneBot Workshop on a number of occasions as well.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Arduino Hardware Interrupt Pins<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">On the Arduino Uno there are only two pins that are hardware interrupt capable:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8896\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-hardware-interrupt-pins.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-hardware-interrupt-pins.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-hardware-interrupt-pins.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Pin 2<\/b><span style=\"font-weight: 400;\"> &#8211; Interrupt vector 0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Pin 3<\/b><span style=\"font-weight: 400;\"> &#8211; Interrupt vector 1.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Not all Arduino boards are limited to 2\u00a0 Hardware Interrupt pins, some Arduino boards have many more. The following chart shows the number of Hardware Interrupts on several common Arduino boards:<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Working with Hardware Interrupts<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Working with Hardware Interrupts is actually pretty simple, as you really only need to do two things:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Write a function to use as your Interrupt Service Routine.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Attach the function to the specific interrupt you want to use, and specify how to trigger it.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">The ISR function should obey the rules about speed and using global variables, but otherwise, it\u2019s just a function.\u00a0 It can have any valid name that you want, but it can\u2019t have input parameters.<\/span><\/p>\n<h4><span style=\"font-weight: 400;\">attachInterrupt Function<\/span><\/h4>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8890\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-attachinterrupt.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-attachinterrupt.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-attachinterrupt.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">To \u201cglue\u201d your function to a specific interrupt, you\u2019ll be using <\/span><a href=\"https:\/\/www.arduino.cc\/reference\/en\/language\/functions\/external-interrupts\/attachinterrupt\/\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">the <\/span><i><span style=\"font-weight: 400;\">attachInterrupt<\/span><\/i><span style=\"font-weight: 400;\"> function<\/span><\/a><span style=\"font-weight: 400;\">.\u00a0 This function has the following syntax and parameters:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Interrupt Vector<\/b><span style=\"font-weight: 400;\"> &#8211; the interrupt that you wish to use. Note that this is the internal Interrupt Vector number and NOT the pin number.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>ISR<\/b><span style=\"font-weight: 400;\"> &#8211; The name of the Interrupt Service Routine function that you are gluing to the interrupt.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Mode<\/b><span style=\"font-weight: 400;\"> &#8211; How you want to trigger the interrupt.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">For Mode, there are four selections:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>RISING<\/b><span style=\"font-weight: 400;\"> &#8211; Triggers when an input goes from LOW to HIGH.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>FALLING<\/b><span style=\"font-weight: 400;\"> &#8211; Triggers when an input goes from HIGH to LOW.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>LOW<\/b><span style=\"font-weight: 400;\"> &#8211; Triggered when the input stays LOW.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>CHANGE <\/b><span style=\"font-weight: 400;\">&#8211; Triggers whenever the input changes state from HIGH to LOW or LOW to HIGH.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">You would normally use <\/span><i><span style=\"font-weight: 400;\">attachInterrupt <\/span><\/i><span style=\"font-weight: 400;\">within the Setup function.<\/span><\/p>\n<h4><span style=\"font-weight: 400;\">digitalPinToInterrupt Function<\/span><\/h4>\n<p><span style=\"font-weight: 400;\">The Interrupt Vector parameter in the <\/span><i><span style=\"font-weight: 400;\">attachInterrupt<\/span><\/i><span style=\"font-weight: 400;\"> function is not the same as the pin number, and it can vary between Arduino boards. A (better) way of obtaining this number is with the <\/span><i><span style=\"font-weight: 400;\">digitalPinToInterrupt <\/span><\/i><span style=\"font-weight: 400;\">function.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The function&#8217;s name is also its description, it accepts a pin number and returns the Interrupt Vector number.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">You can use <\/span><i><span style=\"font-weight: 400;\">digitalPinToInterrupt<\/span><\/i><span style=\"font-weight: 400;\"> directly within the <\/span><i><span style=\"font-weight: 400;\">attachInterrup<\/span><\/i><span style=\"font-weight: 400;\">t function.<\/span><\/p>\n<p><b><i>attachInterrupt(digitalPinToInterrupt(<\/i><\/b><b>pin<\/b><b><i>),ISR,Mode)<\/i><\/b><\/p>\n<p><span style=\"font-weight: 400;\">This is the preferred way of coding for Hardware Interrupts, as it makes the code portable between boards.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Rewriting our Sketch for Hardware Interrupts<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Now that we know more about using Hardware Interrupts, let\u2019s modify our toggle and delay sketch to use them.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Here is an updated version of our sketch, using a Hardware Interrupt:<\/span><\/p>\n<pre class=\"lang:c++ decode:true\" title=\"LED Toggle with Delay &amp; Interrupt\">\/*\r\n  LED Toggle with Delay &amp; Interrupt\r\n  led-toggle-interrupt.ino\r\n  Use pushbutton switch to toggle LED with interrupt\r\n\r\n  DroneBot Workshop 2022\r\n  <blockquote class=\"wp-embedded-content\" data-secret=\"psnsAyOitd\"><a href=\"https:\/\/dronebotworkshop.com\/\">Welcome to the Workshop!<\/a><\/blockquote><iframe class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"&#8220;Welcome to the Workshop!&#8221; &#8212; DroneBot Workshop\" src=\"https:\/\/dronebotworkshop.com\/embed\/#?secret=Us7q4MBLwV#?secret=psnsAyOitd\" data-secret=\"psnsAyOitd\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\r\n*\/\r\n\r\n\/\/ Define LED and switch connections\r\nconst byte ledPin = 13;\r\nconst byte buttonPin = 2;\r\n\r\n\/\/ Boolean to represent toggle state\r\n\r\nvolatile bool toggleState = false;\r\n\r\nvoid checkSwitch() {\r\n  \/\/ Check status of switch\r\n  \/\/ Toggle LED if button pressed\r\n\r\n  if (digitalRead(buttonPin) == LOW) {\r\n    \/\/ Switch was pressed\r\n    \/\/ Change state of toggle\r\n    toggleState = !toggleState;\r\n    \/\/ Indicate state on LED\r\n    digitalWrite(ledPin, toggleState);\r\n  }\r\n}\r\n\r\nvoid setup() {\r\n  \/\/ Set LED pin as output\r\n  pinMode(ledPin, OUTPUT);\r\n  \/\/ Set switch pin as INPUT with pullup\r\n  pinMode(buttonPin, INPUT_PULLUP);\r\n\r\n  \/\/ Attach Interrupt to Interrupt Service Routine\r\n  attachInterrupt(digitalPinToInterrupt(buttonPin),checkSwitch, FALLING); \r\n}\r\n\r\nvoid loop() {\r\n  \r\n  \/\/ 5-second time delay\r\n  Serial.println(\"Delay Started\");\r\n  delay(5000);\r\n  Serial.println(\"Delay Finished\");\r\n  Serial.println(\"..............\");\r\n}\r\n<\/pre>\n<p><span style=\"font-weight: 400;\">We begin similarly, by declaring the pin numbers for our LED and switch.\u00a0 We also use the same boolean for our toggle.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Note that the boolean is made volatile. This is important, as its value is being manipulated within the Interrupt Service Routine. Without the volatile statement, the Arduino IDE compiler may try and over-optimize the code and remove the variable.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Our <\/span><i><span style=\"font-weight: 400;\">checkSwitch<\/span><\/i><span style=\"font-weight: 400;\"> function is almost identical to what it was before, the only difference is that we have removed the <\/span><i><span style=\"font-weight: 400;\">delay<\/span><\/i><span style=\"font-weight: 400;\"> function. This is because we will be using<\/span><i><span style=\"font-weight: 400;\"> checkSwitch<\/span><\/i><span style=\"font-weight: 400;\"> as our Interrupt Service Routine, and we can\u2019t use a <\/span><i><span style=\"font-weight: 400;\">delay<\/span><\/i><span style=\"font-weight: 400;\"> inside an ISR.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In Setup we do the usual <\/span><i><span style=\"font-weight: 400;\">pinMode<\/span><\/i><span style=\"font-weight: 400;\"> commands, initialize the serial monitor, and then run <\/span><i><span style=\"font-weight: 400;\">attachInterrupt<\/span><\/i><span style=\"font-weight: 400;\"> to attach the <\/span><i><span style=\"font-weight: 400;\">checkSwitch<\/span><\/i><span style=\"font-weight: 400;\"> function to the Hardware Interrupt on pin 2. We use a FALLING mode, as we want to capture when we press (and ground) the switch.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">All that we have in the Loop is the delay, which will now run continuously. Any switch activity will now be handled by the interrupt.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Load the sketch and play with the pushbutton while you observe both the LED and serial monitor. You should see that the toggle works despite the Loop always being inside a delay.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">As you can see, Hardware Interrupts are a much more efficient method of capturing switch inputs.<\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Pin Change Interrupts<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Pin Change Interrupts are another form of a hardware interrupt. Unlike the interrupts we have just used, they are not restricted to specific pins, all the pins can be used for Pin Change Interrupts.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The catch is that Pin Change Interrupts are grouped into Ports, and all the pins on the same port create the same Pin Change Interrupt. This is fine if you are only using one, otherwise, you\u2019ll need to figure out which pin caused the interrupt.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Pin Change Interrupts are restricted, as their name might imply, to only monitoring a CHANGE of logic state. So a switch press will generate two interrupts, one when the switch is pressed and a second one when it is released. If you need to know if the interrupt was caused by a HIGH or LOW input, then you\u2019ll have to figure that out yourself.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Pin Change Ports<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Almost every pin on the ATmega328 chip that the Arduino Uno (and other boards) are based upon can support 24 Pin Change Interrupts.\u00a0 That includes the two pins used for the 16MHz crystal oscillator.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8900\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-ports.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-ports.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-ports.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">On the Arduino Uno, 20 pins are available for Pin Change Interrupts, and they are divided into three ports.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8897\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-b.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-b.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-b.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Pins 8 through 13 are on Port B.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8898\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-c.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-c.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-c.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Pins A0 to A5 are on Port C.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8899\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-d.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-d.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-pin-change-port-d.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Pins 0 to 7 are on Port D.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Working with Pin Change Interrupts<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">In order to use Pin Change Interrupts, you\u2019ll need to do the following:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Determine which pin(s) that you want to use.\u00a0 This will also tell you which port(s) you\u2019ll need to use.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Enable the port(s) that you need.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Enable the pin(s) within that port that must be enabled for interrupts.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Edit the appropriate Interrupt Service Routine(s). If you are using more than one pin on the same port, then the ISR will need to be able to determine which pin caused the interrupt.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Let\u2019s look at those steps in a bit more detail. For our example we will just use an individual pin, later we will run a sketch that uses two pins on the same port.<\/span><\/p>\n<h4><span style=\"font-weight: 400;\">Select the Port<\/span><\/h4>\n<p><span style=\"font-weight: 400;\">The first step is to enable the appropriate port, which you\u2019ll determine based on the pin number. To enable the port, you will use the <\/span><i><span style=\"font-weight: 400;\">Pin Change Interrupt Control Register<\/span><\/i><span style=\"font-weight: 400;\"> or PCICR.\u00a0<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8908\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-1.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-1.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-1.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">The PCICR has three bits of interest, Bit 0, Bit 1, and Bit 2. Each bit is associated with one of the ports, and setting it to 1 will enable the port.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In Setup, you&#8217;ll write a binary number to the PCICR to set the appropriate bit(s) to 1.\u00a0 You can, of course, enable more than one port.<\/span><\/p>\n<h4><span style=\"font-weight: 400;\">Enable\/Disable the Pins on the Port<\/span><\/h4>\n<p><span style=\"font-weight: 400;\">After enabling the port, you\u2019ll need to enable the pin(s) that you want to use for Pin Change Interrupts.\u00a0 You do that by modifying the <\/span><i><span style=\"font-weight: 400;\">Pin Change Mask<\/span><\/i><span style=\"font-weight: 400;\"> for your selected port.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8909\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-2.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-2.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-2.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">There are three Pin Change Masks, and each one can enable or disable 8 pins. To enable a pin, you write a \u201c1\u201d to it. You can enable as many pins as you require, remember you\u2019ll need to find a way to differentiate between them in your Interrupt Service Routine.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8910\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-3.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-3.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-3.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<h4><span style=\"font-weight: 400;\">Interrupt Service Routine<\/span><\/h4>\n<p><span style=\"font-weight: 400;\">Unlike Hardware Interrupts, you don\u2019t just create an Interrupt Service Routine and give it any random name. With Pin Change Interrupts, the ISR has already been defined for you, so you\u2019ll need to use the correct one for your port.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">There are three ports and thus three ISRs, which are named as shown here:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8911\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-isr.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-isr.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-isr.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">All the same rules regarding Interrupt Service Routines apply to the ISR you use with Pin Change Interrupts. Keep it short and use volatile global variables.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Experimenting with Pin Change Interrupts<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">In order to run the next couple of examples, we will need to add another pushbutton and LED to our Arduino. The final hookup is shown here:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8913\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-test-hookup.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-test-hookup.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/pin-change-test-hookup.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">So we now have:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A pushbutton on pin D2.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A pushbutton on pin D7.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">An LED on pin D11.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">An LED on pin D13.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Note that the two pushbutton switches, on D2 and D7, are on the same port, port D.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Pin Change Interrupt Example 1 &#8211; Simple Interrupt<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">The first example we will run will illustrate how to code for Pin Change Interrupts.\u00a0 We will only be using one switch and one\u00a0 LED in this experiment. Note that our switch is on pin D7, which is not a Hardware Interrupt pin.\u00a0 That doesn\u2019t matter, as we\u2019ll be sensing it with a Pin Change Interrupt!<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We will be toggling the state of an LED every time we get an interrupt on pin D7. One important thing to keep in mind is that we will be sensing an input CHANGE of state, so a pushbutton will produce two interrupts &#8211; one when pressing it down and another one when releasing it.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">This will make our LED operate a lot like it was just wired in series with the switch!<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Here is our sketch:<\/span><\/p>\n<pre class=\"lang:c++ decode:true \" title=\"Pin Change Interrupt Test\">\/*\r\n  Pin Change Interrupt Test\r\n  pin-change-test.ino\r\n  Demonstrates use of Pin Change Interrupt\r\n  Input on D7, LED on D13\r\n\r\n  DroneBot Workshop 2022\r\n  <blockquote class=\"wp-embedded-content\" data-secret=\"psnsAyOitd\"><a href=\"https:\/\/dronebotworkshop.com\/\">Welcome to the Workshop!<\/a><\/blockquote><iframe class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"&#8220;Welcome to the Workshop!&#8221; &#8212; DroneBot Workshop\" src=\"https:\/\/dronebotworkshop.com\/embed\/#?secret=Us7q4MBLwV#?secret=psnsAyOitd\" data-secret=\"psnsAyOitd\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\r\n*\/\r\n\r\n\/\/ LED and switch\r\nconst byte ledPin = 13;\r\nconst byte buttonPin = 7;\r\n\r\n\/\/ Boolean to represent toggle state\r\nvolatile bool togglestate = false;\r\n\r\nvoid setup() {\r\n\r\n  \/\/ Set LED as output\r\n  pinMode(ledPin, OUTPUT);\r\n\r\n  \/\/ Set switch as input with pullup\r\n  pinMode(buttonPin, INPUT_PULLUP);\r\n\r\n\r\n  \/\/ Enable PCIE2 Bit3 = 1 (Port D)\r\n  PCICR |= B00000100;\r\n  \/\/ Select PCINT23 Bit7 = 1 (Pin D7)\r\n  PCMSK2 |= B10000000;\r\n\r\n}\r\n\r\nvoid loop() {\r\n  \/\/ No code in Loop\r\n}\r\n\r\nISR (PCINT2_vect)\r\n{\r\n  \/\/ Interrupt for Port D\r\n  \/\/ Invert toggle state\r\n  togglestate = !togglestate;\r\n  \/\/ Indicate state on LED\r\n  digitalWrite(ledPin, togglestate);\r\n\r\n\r\n}\r\n<\/pre>\n<p><span style=\"font-weight: 400;\">We start by defining pins for the switch and LED.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Next we create a volatile boolean to represent the toggle state.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In Setup, we use the <\/span><i><span style=\"font-weight: 400;\">pinMode<\/span><\/i><span style=\"font-weight: 400;\"> function to define our inputs and outputs.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">And then we set up our Pin Change Interrupt. We modify the PCICR register to let it know we want to use port D, and we modify port D\u2019s mask PCMSK2 to set pin D7 as an interrupt input.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We don\u2019t have any code in the Loop, as we are doing everything with an interrupt service routine.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The Interrupt Service Routine is next, and as we are using port D we use <\/span><i><span style=\"font-weight: 400;\">ISR (PCINT2_vect)<\/span><\/i><span style=\"font-weight: 400;\">.\u00a0 In the ISR we flip the state of the <\/span><i><span style=\"font-weight: 400;\">toggleState<\/span><\/i><span style=\"font-weight: 400;\"> variable and use it to drive the LED.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Load the code and try it out. The LED should come on when you hold the switch down and go off when you release it. Which, of course, is a real overkill using a microcontroller, but it does demonstrate Pin Change Interrupts!<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Pin Change Interrupt Example 2 &#8211; Multiple Interrupts on the Same Port<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">In the previous example, we were just able to act upon the Pin Change Interrupt, as only one pin on our port was enabled for interrupts. There was no question about what had caused the interrupt.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">But how do you deal with it when you enable two or more pins on the same port for Pin Change Interrupts? You will need to determine who caused the interrupt so that you can act accordingly.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In this example, we will have two pushbuttons and two LEDs. Each pushbutton will act as a toggle for its respective LED. That means that we need to know two things when we get an interrupt:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">What pin caused the interrupt?<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Was it LOW or HIGH?<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">We will answer both of those questions within our sketch:<\/span><\/p>\n<pre class=\"lang:c++ decode:true \" title=\"Multiple Pin Change Interrupt Demo\">\/*\r\n  Multiple Pin Change Interrupt Demo\r\n  pin-change-multiple-test.ino\r\n  Demonstrates Pin Change Interrupts with two on same port\r\n  Inputs on D2 &amp; D7, LEDs on D11 and D13\r\n\r\n  DroneBot Workshop 2022\r\n  <blockquote class=\"wp-embedded-content\" data-secret=\"psnsAyOitd\"><a href=\"https:\/\/dronebotworkshop.com\/\">Welcome to the Workshop!<\/a><\/blockquote><iframe class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"&#8220;Welcome to the Workshop!&#8221; &#8212; DroneBot Workshop\" src=\"https:\/\/dronebotworkshop.com\/embed\/#?secret=Us7q4MBLwV#?secret=psnsAyOitd\" data-secret=\"psnsAyOitd\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\r\n*\/\r\n\r\n\/\/ LEDs and switchs\r\nconst byte ledPin1 = 11;\r\nconst byte ledPin2 = 13;\r\nconst byte buttonPin1 = 2;\r\nconst byte buttonPin2 = 7;\r\n\r\n\/\/ Booleans for input states\r\nvolatile bool D2_state = LOW;\r\nvolatile bool D7_state = LOW;\r\n\r\nvoid setup() {\r\n\r\n  \/\/ Set LEDs as outputs\r\n  pinMode(ledPin1, OUTPUT);\r\n  pinMode(ledPin2, OUTPUT);\r\n\r\n  \/\/ Set switches as inputs with pullups\r\n  pinMode(buttonPin1, INPUT_PULLUP);\r\n  pinMode(buttonPin2, INPUT_PULLUP);\r\n\r\n  \/\/ Enable PCIE2 Bit3 = 1 (Port D)\r\n  PCICR |= B00000100;\r\n  \/\/ Enable PCINT18  &amp; PCINT23 (Pins D2 &amp; D7)\r\n  PCMSK2 |= B10000100;\r\n\r\n}\r\n\r\nvoid loop() {\r\n  \r\n  \/\/ Loop code\r\n\r\n}\r\n\r\nISR (PCINT2_vect)\r\n{\r\n  \/\/ Port D Interrupt occured\r\n  \r\n  \/\/ Check if this was D2\r\n  if (digitalRead(buttonPin1) == LOW) {\r\n    \/\/Pin D2 triggered the ISR on a Falling pulse\r\n    D2_state = !D2_state;\r\n    \/\/Set LED 1 to state of D2_state boolean\r\n    digitalWrite(ledPin1, D2_state);\r\n  }\r\n\r\n  \/\/ Check if this was D7\r\n  if (digitalRead(buttonPin2) == LOW) {\r\n    \/\/Pin D7 triggered the ISR on a Falling pulse\r\n    D7_state = !D7_state;\r\n    \/\/Set LED 2 to state of D7_state boolean\r\n    digitalWrite(ledPin2, D7_state);\r\n  }\r\n\r\n}\r\n<\/pre>\n<p><span style=\"font-weight: 400;\">The sketch begins as you would expect, we define a bunch of variables for the LEDs and switches and two booleans, one for each toggle state.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In the Setup, we set the <\/span><i><span style=\"font-weight: 400;\">pinModes<\/span><\/i><span style=\"font-weight: 400;\"> for the switches and LEDs, again using the internal pull-up resistors for the inputs.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We then enable Port D, as we did in the previous sketch, by writing a \u201c1\u201d to bit 2 of the PCICR register.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Next, we write a \u201c1\u201d to both bits 7 and 2 of the PCMSK2 mask, to let it know that pins D7 and D2 are to be treated as Pin Change Interrupts.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Again there is no code in the Loop, everything is being done in the Interrupt Service Routine.\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400;\">That routine is ISR (PCINT2_vect), the ISR for Port D., which is the same ISR we used in the previous sketch. Only this time, we will need to figure out if it was pin D2 or D7 that caused the interrupt.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We are looking for a LOW condition in this sketch, as we want to toggle the button when the switch is pressed, but not when it is released.\u00a0 Also, we use a couple of if statements along with a <\/span><i><span style=\"font-weight: 400;\">digitalRead<\/span><\/i><span style=\"font-weight: 400;\"> to check each input and determine if it is currently LOW. If it is, then we toggle the respective boolean and use it to control the LED.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Load the sketch and give it a test. The pushbutton tied to pin D2 should control the LED on pin D11, and the button on D7 should work with the LED on pin D13.\u00a0 You should be able to toggle each of them independently.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Pin Change Interrupts can be very useful when scanning a group or matrix of switches, or when you need an external interrupt but haven\u2019t got a Hardware Interrupt pin to spare.<\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Timer Interrupts<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Timer interrupts don\u2019t use external signals. Instead, these interrupts are generated in software, and their timing is based upon the Arduino Uno\u2019s 16 MHz clock oscillator.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">You\u2019ve likely been using Timer Interrupts without realizing it, as several popular libraries, such as the Servo and Tone libraries, use timer interrupts internally. Bear in mind that if you are using a library that makes use of the timers, you\u2019ll need to know that so that you don\u2019t write conflicting code.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Arduino Uno Timers<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">The Arduino Uno has three internal timers, Timer0, Timer1, and Timer2.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8906\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-timers.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-timers.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-timers.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">These timers are not the same, as Timer1 is a 16-bit timer, whereas the other two timers are just 8-bit timers. The number of bits determines the maximum number that the timer can count to, 256 for the 8-bit timers and 65,536 for the 16-bit one.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The value in these timers is incremented by either the clock frequency or a fraction of it. You can use software to determine the count you wish to set the interrupt to trigger at, you can also trigger an interrupt when the timer overflows.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Dividing the Clock Frequency<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">The Timers are clocked by the 16 MHz oscillator which is internal to the ATmega328.\u00a0<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8895\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-clock.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-clock.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-clock.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Every cycle of the clock is a timer \u201ctick\u201d, so at 16 MHz a \u201ctick\u201d would be a period of 62.5 nanoseconds. This is a pretty short period, and for many timing applications, it would be too short to be of much practical use.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">To slow down the clock signal, the ATmega328 has a \u201cPrescaler\u201d, essentially a divider for the clock frequency. The Prescaler can divide the clock down to a more manageable lower frequency, you can select from a number of common divisions to create pulses as long as 64us.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8901\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Each timer has three Clock Select Bits, and the value of these bits can determine the Prescaler settings, as well as the timing source.\u00a0 You can also stop the clock entirely by setting all the Clock Select Bits to zero.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8902\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-0.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-0.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-0.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Timer0, an 8-bit Timer, uses bits CS01, CS02, and CS03.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8903\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-1.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-1.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-1.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Timer1, the 16-bit timer, uses bits CS10, CS11, and CS12.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8904\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-2.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-2.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-prescaler-timer-2.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Timer2, another 8-bit timer, uses bits CS20, CS21, and CS22.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Using Timer Interrupts<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">Timer Interrupts can be operated in a couple of different modes, including <\/span><i><span style=\"font-weight: 400;\">Compare Match Mode<\/span><\/i><span style=\"font-weight: 400;\"> and <\/span><i><span style=\"font-weight: 400;\">Overflow Mode<\/span><\/i><span style=\"font-weight: 400;\">.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In Compare Match Mode, you place a counter value into a Compare Match Register. The timer interrupt is generated when the timer counter matches the value in that register.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In Overflow Mode the timer interrupt is generated when the timer reaches the end of its count, an interrupt is generated and the timer resets to zero and begins counting again.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">By combining the Compare Match Register with a Prescaler you can get pretty well any timing period you want, assuming it is in the range of your timer (the 8-bit timers will only divide by a maximum of 255).<\/span><\/p>\n<p><span style=\"font-weight: 400;\">The formula for determining the output frequency, and thus the period, of a timer, is as follows:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8894\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-timer-clock-calculation.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-timer-clock-calculation.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-timer-clock-calculation.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><b><i>Clock\/(Prescaler x (Compare Match Register + 1)) = Frequency<\/i><\/b><\/p>\n<p><span style=\"font-weight: 400;\">If you know the frequency that you want and want to determine the Compare Match Register value, you can rewrite the formula as follows:<\/span><\/p>\n<p><b><i>[Clock\/(Prescaler x Frequency)] -1 = Compare Match Register<\/i><\/b><\/p>\n<p><span style=\"font-weight: 400;\">Using the above formulas we can calculate that to get a 1 Hz output we can use a Prescaler of 1024 and a Compare Match Register of 15,624. As this value exceeds 255 we would be limited to using Timer1, the 16-bit timer.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Timer Interrupt Service Routines<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">As with the Pin Change Interrupts the names of the interrupt service routines for Timer Interrupts have already been determined for you.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-8905\" src=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-timer-isr.jpg?resize=750%2C422&#038;ssl=1\" alt=\"\" width=\"750\" height=\"422\" srcset=\"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-timer-isr.jpg?w=768&amp;ssl=1 768w, https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-uno-timer-isr.jpg?resize=300%2C169&amp;ssl=1 300w\" sizes=\"(max-width: 750px) 100vw, 750px\" data-recalc-dims=\"1\" \/><\/p>\n<p><span style=\"font-weight: 400;\">Each timer has two ISRs associated with it, one for Compare Match Mode and the other for Overflow Mode.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In the above diagram, the\u201dx\u201d after the word \u201cTIMER\u201d should be replaced by the timer number, such as 0, 1, or 2.<\/span><\/p>\n<h3><span style=\"font-weight: 400;\">Simple Timer Example<\/span><\/h3>\n<p><span style=\"font-weight: 400;\">This very simple timer example sets up a timer for a 2 HZ output, or twice a second. We then use the timer to control an LED, so essentially we are building the Blink sketch!<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We will be using an Arduino Uno and an LED (with dropping resistor) on pin 13. If you wish, you can just grab one of the previous experiments, or just use the built-in LED on the Arduino board.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Here is the sketch that we will be using:<\/span><\/p>\n<pre class=\"lang:c++ decode:true \" title=\"Arduino Timer Interrupt Flash Demo\">\/*\r\n  Arduino Timer Interrupt Flash Demo\r\n  timer-int-flash.ino\r\n  Flash LED using Timer1\r\n\r\n  DroneBot Workshop 2022\r\n  <blockquote class=\"wp-embedded-content\" data-secret=\"psnsAyOitd\"><a href=\"https:\/\/dronebotworkshop.com\/\">Welcome to the Workshop!<\/a><\/blockquote><iframe class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; clip: rect(1px, 1px, 1px, 1px);\" title=\"&#8220;Welcome to the Workshop!&#8221; &#8212; DroneBot Workshop\" src=\"https:\/\/dronebotworkshop.com\/embed\/#?secret=Us7q4MBLwV#?secret=psnsAyOitd\" data-secret=\"psnsAyOitd\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\r\n*\/\r\n\r\n\/\/ Define the LED pin\r\n#define ledPin 13\r\n\r\n\/\/ Define timer compare match register value\r\nint timer1_compare_match;\r\n\r\n\r\nISR(TIMER1_COMPA_vect)\r\n\/\/ Interrupt Service Routine for compare mode\r\n{\r\n  \/\/ Preload timer with compare match value\r\n  TCNT1 = timer1_compare_match;\r\n  \r\n  \/\/ Write opposite value to LED\r\n  digitalWrite(ledPin, digitalRead(ledPin) ^ 1);\r\n}\r\n\r\nvoid setup()\r\n{\r\n  \/\/ Set LED as output\r\n  pinMode(ledPin, OUTPUT);\r\n\r\n  \/\/ Disable all interrupts\r\n  noInterrupts();\r\n\r\n  \/\/ Initialize Timer1\r\n  TCCR1A = 0;\r\n  TCCR1B = 0;\r\n\r\n  \/\/ Set timer1_compare_match to the correct compare match register value\r\n  \/\/ 256 prescaler &amp; 31246 compare match = 2Hz\r\n  timer1_compare_match = 31249;\r\n\r\n  \/\/ Preload timer with compare match value\r\n  TCNT1 = timer1_compare_match;\r\n\r\n  \/\/ Set prescaler to 256\r\n  TCCR1B |= (1 &lt;&lt; CS12);\r\n\r\n  \/\/ Enable timer interrupt for compare mode\r\n  TIMSK1 |= (1 &lt;&lt; OCIE1A);\r\n\r\n  \/\/ Enable all interrupts\r\n  interrupts();\r\n}\r\n\r\n\r\n\r\nvoid loop()\r\n{\r\n\r\n}\r\n<\/pre>\n<p><span style=\"font-weight: 400;\">In this sketch, we are using the Compare Match Mode, so after we define an LED pin, we also create an integer to hold the compare match register value.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Next, our Interrupt Service Routine. As we are using Compare Match Mode on Timer1, we will use<\/span><i><span style=\"font-weight: 400;\"> ISR(TIMER1_COMPA_vect)<\/span><\/i><span style=\"font-weight: 400;\">.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">In the ISR we do two things:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Preload the timer with the compare match value, to start the cycle again<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Flip the value of the LED.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">In Setup, we set our LED pin as an output. We then temporarily disable all interrupts, to prevent one from coming along while we are still setting things up.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We initialize Timer1 with two commands and then set up our compare match value. Since we are looking to achieve 2 Hz, we calculate that 31246 is a good value if we use a Prescaler of 256.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">We then preload our timer with the compare match value, set our Prescaler for 256, and enable interrupts in compare match mode.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Finally, we re-enable all the interrupts.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Load the sketch and observe the LED flashing. After the thrill of that is gone, experiment with different Prescaler and Compare Match values.<\/span><\/p>\n<h2><span style=\"font-weight: 400;\">Conclusion<\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Interrupts are a great way to build projects that require precise timing or a responsive user interface.\u00a0 While most of us have dabbled with Hardware Interrupts, many people shy away from Pin Change or Timer interrupts, which is a shame as they are so useful and the binary coding isn\u2019t really that difficult once you understand the use of the registers.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">I\u2019d encourage you to incorporate interrupts into your next design.\u00a0 Remember, in some cases, it isn\u2019t rude to be interrupted!<\/span><\/p>\n<p>&nbsp;<\/p>\n<div class=\"dbwspartsbox\">\n<h3>Parts List<\/h3>\n<p><em>Here are some components that you might need to complete the experiments in this article. Please note that some of these links may be affiliate links, and the DroneBot Workshop may receive a commission on your purchases. This does not increase the cost to you and is a method of supporting this ad-free website.<\/em><\/p>\n<p>COMING SOON!<\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<h3><span style=\"font-weight: 400;\">Resources<\/span><\/h3>\n<p><a href=\"https:\/\/s3.amazonaws.com\/download.dronebotworkshop.com\/Arduino+Interrupts+-+DroneBot+Workshop.zip\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">Code Samples<\/span><\/a><span style=\"font-weight: 400;\"> &#8211; All the code used in this article, packed up nicely in a ZIP file.<\/span><\/p>\n<p><a href=\"https:\/\/www.arduino.cc\/reference\/en\/language\/functions\/external-interrupts\/attachinterrupt\/\" target=\"_blank\" rel=\"noopener\"><span style=\"font-weight: 400;\">attachInterrupt<\/span><\/a><span style=\"font-weight: 400;\"> &#8211; Reference for the attachInterrupt function used with Hardware Interrupts.<\/span><\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>If your project needs a responsive user interface or has precision timing requirements, then interrupts are the key to getting it to work smoothly.<\/P> Today we will learn how to use Hardware, Pin Change and Timer Interrupts with the Arduino Uno.<\/p>\n","protected":false},"author":1,"featured_media":8914,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[9,90],"tags":[44],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/i0.wp.com\/dronebotworkshop.com\/wp-content\/uploads\/2022\/05\/arduino-interrupts.jpg?fit=768%2C432&ssl=1","jetpack_shortlink":"https:\/\/wp.me\/p74ClK-2jn","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/posts\/8889"}],"collection":[{"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/comments?post=8889"}],"version-history":[{"count":10,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/posts\/8889\/revisions"}],"predecessor-version":[{"id":9740,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/posts\/8889\/revisions\/9740"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/media\/8914"}],"wp:attachment":[{"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/media?parent=8889"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/categories?post=8889"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dronebotworkshop.com\/wp-json\/wp\/v2\/tags?post=8889"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}