{"id":3712,"date":"2020-06-08T15:55:52","date_gmt":"2020-06-08T13:55:52","guid":{"rendered":"https:\/\/home.et.utwente.nl\/slootenvanf\/?p=3712"},"modified":"2025-03-19T10:08:39","modified_gmt":"2025-03-19T09:08:39","slug":"countdown-timers-tasks-in-parallel","status":"publish","type":"post","link":"https:\/\/home.et.utwente.nl\/slootenvanf\/2020\/06\/08\/countdown-timers-tasks-in-parallel\/","title":{"rendered":"Countdown timers and executing tasks in parallel on an Arduino"},"content":{"rendered":"\n

Most examples in this article use an OLED display<\/a>.<\/p>\n\n\n\n

Countdown timer example<\/h2>\n\n\n\n
\"\"<\/figure>\n\n\n\n

In its simplest form, a countdown timer can be coded like this, using the loop() f<\/em>or repetition (no for- or while-loop needed!):<\/p>\n\n\n\n

void loop() {\n  if (count>=0) { \/\/ if counter not finished\n      sprintf(buf, \"%2d\", count);\n      display.draw2x2String(4,3,buf); \/\/ show the counter\n      count = count - 1; \/\/ decrease counter\n  }\n  delay(1000); \/\/ wait one second\n}<\/code><\/pre>\n\n\n\n
\"\"<\/a><\/figure>\n\n\n\n
Download the sketch: oled_display_countdown_start_button.ino<\/code><\/a><\/p>\n\n\n\n
Full simulation including breadboard on Wokwi:<\/a><\/p>\n\n\n\n
\"\"<\/a><\/figure>\n\n\n\n
This will countdown from 10 to 0 in ten seconds after the button is pressed. If you prefer to display the number as a time, like MM:SS, you can realize that as follows:<\/p>\n\n\n\n
int min = count\/60;\nint sec = count%60;\nsprintf(buf, \"%02d:%02d\", min, sec);\ndisplay.draw2x2String(2,3,buf);<\/code><\/pre>\n\n\n\n
Full example : oled_display_countdown_start_button2.ino<\/code><\/a><\/p>\n\n\n\n
Both examples use a button to start the timer. This is realized by a waiting loop (a loop which does nothing, except for checking its condition) as the last line in setup()<\/em>:<\/p>\n\n\n\n
while(digitalRead(START_BTN)==HIGH) ;<\/code><\/pre>\n\n\n\n
Note the empty statement: ‘;’ does nothing, thus waits for the button to be pressed (becomes LOW).<\/p>\n\n\n\n
Another example: push-and-hold<\/h2>\n\n\n\n
\"\"<\/a><\/figure>\n\n\n\n
Start a sketch if button held for a period. If released prior to the period abort. Uses the millis()<\/a> function to keep track of time (in milliseconds). Learn why using delay() in cases like this is not useful.<\/a><\/p>\n\n\n\n
    if (millis() >= time_start + period) { \/\/ holding period over?\n      display.clearLine(0);\n      display.drawString(0, 0, \"DONE\"); \/\/ time to hold the button for period succesfully done\n      status = 1;\n    }\n    else if (digitalRead(START_BTN) == HIGH) { \/\/ button released?\n      \/\/ abort, button was released\n      display.clearLine(0);\n      display.drawString(0, 0, \"ABORT\");\n      status = 2;\n    }<\/code><\/pre>\n\n\n\n
Download the example: oled_display_hold_button.ino<\/strong><\/a> (Wokwi simulation here<\/a>)<\/p>\n\n\n\n
Another example: turn Arduino on or off by holding a button: button_on_off_long_press.ino<\/strong><\/a> (Wokwi simulation here<\/a>)<\/p>\n\n\n\n
Parallel tasks, advanced timer example<\/h2>\n\n\n\n
About running tasks in the background: it is true that the loop()<\/em> is actually a kind of ‘single task’ that does not allow (or is difficult) to run things in parallel or in the background.
However, because the Arduino is fairly fast, tasks that are performed in serial (one after the other) may still appear to the user as if they are being performed simultaneously.
It is important that you do not use delays, so that everything is executed as quickly as possible.
Instead of using delays, you can then keep the time and have things done at a certain time: eg. make an LED blink every 300ms and read all buttons at the same time (as quickly as possible).
The example below uses that: three tasks (in the loop) are performed in serial, but for the user it looks like they occur in parallel, because they do not contain any delays.<\/p>\n\n\n\n
\"\"<\/a><\/figure>\n\n\n\n
See the code:<\/p>\n\n\n\n