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TECHNICAL ARTICLE Disclaimer The views, opinions, positions or strategies expressed by the author and those providing comments are theirs alone, and do not necessarily reflect the views, opinions, positions or strategies of anybody else. Das Blinkenlights [1] We’ll have a closer look at the blinking LED Arduino sketch we saw last time (Figure 1). ACHTUNG! ALLES TURISTEN UND NONTEKNISCHEN LOOKEN- PEEPERS! DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRA- BEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPEN- CORKEN MIT SPITZENSPARKSEN. IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBER- NECKEN SIGHTSEEREN KEEPEN DAS COTTON- PICKEN HÄNDER IN DAS POCKETS MUSS. ZO RE- LAXEN UND WATSCHEN DER. BLINKENLICHTEN. Dissection of BlinkWithoutDelay [3] Sketch Programs written for the Processing [4] programming language are called sketches. These sketches are typically written using the text editor that comes with Processing. It has features for cutting/pasting and for searching/replacing text. Sketches written for Processing should have a .pde file extension, which stands for Processing Development Environment. Arduino borrowed this concept from Processing and programs that are being uploaded to and run on an Arduino board are called sketches as well. To distinguish Arduino from Processing sketches, .ino should be used as a file extension, which stands for Arduino (Figure 2). Comments Robert Berger Embedded Software Specialist Arduino for mere m0rtals - PART 4 Everything between the /* (line 1) and */ (line 22) is ignored by the Arduino when it runs the sketch (the * (lines 8, 9) at the start of each line is only there to make the comment look pretty, and isn’t required). Comments are for people who read your code and for you and try EEWeb | Electrical Engineering Community Visit www.eeweb.com 16 TECHNICAL ARTICLE
TECHNICAL ARTICLE Figure 1: Try telnet towels.blinkenlights.nl [2] Listing 1: BlinkWithoutDelay.ino /* Blink without Delay 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Turns on and off a light emitting diode (LED) connected to a digital pin, without using the delay() function. This means that other code can run at the same time without being interrupted by the LED code. The circuit: * LED attached from pin 13 to ground * Note: on most Arduinos, there is already an LED on the board that’s attached to pin 13, so no hardware is needed for this example. created 2005 by David A. Mellis modified 8 Feb 2010 by Paul Stoffregen This example code is in the public domain http://www.arduino.cc/en/Tutorial/BlinkWithoutDelay */ Figure 2 to understand what you wrote a long time ago. They (hopefully) explain what the program does, how it works, or why it’s written the way it is. It’s good practice to comment on your sketches and to keep the comments up-to-date when you modify the code. Remember, as a good ”open-source citizen,” to share your code so others can learn from or modify/improve your code. There’s another style for short, single-line comments. These start with // (e.g on line 26) and continue to the end of the line. To delay() or not to delay()? [5] The delay() function mentioned on line 4 and the hint not to use it so other code can run already looks weird to someone who used a RTOS or Unix/Linux before. Let’s have a closer look at it. From the FreeRTOS call vTaskDelay(500/portTICK RATE MS) [6], you would expect to delay a task for 500 msec. The fact that this API call delays/blocks a task for 500 msec means that it allows tasks with a lower priority to run until the time expires. In Linux usleep(500) [7], it would block the calling process for 500 msec and allow processes with a lower priority to run until the time expires – kind of. Description The delay() function pauses the program for the amount of time (in milliseconds) specified as parameter. (Remember: there are 1000 milliseconds in a second.) Syntax delay(ms) Parameters ms: the number of milliseconds to pause (unsigned long) Returns nothing (Figure 3) Caveat While it is easy to create a blinking LED with the delay() function, and many sketches use short delays for such tasks as switch debouncing, the use of delay() in a sketch has significant drawbacks. No other reading of sensors, mathematical calculations, or pin manipulation EEWeb | Electrical Engineering Community Visit www.eeweb.com 17 TECHNICAL ARTICLE
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