Arduino UNO R4 - Blink LED Without Delay

Imagine that the Arduino UNO R4 needs to do two tasks: blink an LED and detect when a button is pressed. If we use the delay() function, the Arduino UNO R4 might miss some button presses. In this tutorial, we'll learn how to make the Arduino UNO R4 blink an LED and monitor a button to ensure it detects every button press.

We will go through three examples below and compare their differences.

Arduino UNO R4 Blink LED

※ NOTE THAT:

  • This method does more than just make LED blink and check button status. It allows Arduino UNO R4 to perform multiple tasks simultaneously without interruption.
  • This tutorial gives detailed information to help you learn how it works. For simplicity, you can use Arduino UNO R4 - LED library.

Hardware Preparation

1×Arduino UNO R4 WiFi
1×Arduino UNO R4 Minima (Alternatively)
1×USB Cable Type-C
1×LED
1×220 ohm resistor
1×Push Button
1×(Optional) Panel-mount Push Button
1×Breadboard
1×Jumper Wires
1×(Optional) 9V Power Adapter for Arduino UNO R4
1×(Recommended) Screw Terminal Block Shield for Arduino Uno
1×(Optional) Transparent Acrylic Enclosure For Arduino Uno

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you. We appreciate your support.

Overview of LED and Button

Learn about LED and button (pinout, how they work, how to program, etc.) in these tutorials:

Wiring Diagram

The wiring diagram between Arduino UNO R4 LED

This image is created using Fritzing. Click to enlarge image

Arduino UNO R4 Code - With Delay

/* * This Arduino UNO R4 code was developed by newbiely.com * * This Arduino UNO R4 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-uno-r4/arduino-uno-r4-blink-led-without-delay */ #define LED_PIN 3 // The Arduino UNO R4 pin connected to the LED #define BUTTON_PIN 7 // The Arduino UNO R4 pin connected to the button #define BLINK_INTERVAL 1000 // interval at which to blink LED (milliseconds) int led_state = LOW; // led_state used to set the LED int prev_button_state = LOW; // will store last time button was updated void setup() { Serial.begin(9600); // set the digital pin as output pinMode(LED_PIN, OUTPUT); // set the digital pin as an input pinMode(BUTTON_PIN, INPUT_PULLUP); } void loop() { // if the LED is off turn it on and vice-versa led_state = (led_state == LOW) ? HIGH : LOW; // set the LED with the led_state of the variable digitalWrite(LED_PIN, led_state); delay(BLINK_INTERVAL); // If button is pressed during this time, Arduino CANNOT detect int button_state = digitalRead(BUTTON_PIN); if (button_state != prev_button_state) { // print out the state of the button: Serial.println(button_state); // save the last state of button prev_button_state = button_state; } // DO OTHER WORKS HERE }

Detailed Instructions

Follow these instructions step by step:

  • If this is your first time using the Arduino Uno R4 WiFi/Minima, refer to the tutorial on setting up the environment for Arduino Uno R4 WiFi/Minima in the Arduino IDE.
  • Wire the components according to the provided diagram.
  • Connect the Arduino Uno R4 board to your computer using a USB cable.
  • Launch the Arduino IDE on your computer.
  • Select the appropriate Arduino Uno R4 board (e.g., Arduino Uno R4 WiFi) and COM port.
  • Copy the provided code and paste it into the Arduino IDE.
  • Click the Upload button in the Arduino IDE to transfer the code to the Arduino UNR R4.
Arduino IDE - How to Upload Code
  • Open the Serial Monitor.
  • Push the button four times.
  • Observe the LED: It switches on and off every second.
  • Check the display on the Serial Monitor.
COM6
Send
1 0
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
  • Some button presses were not shown on the Serial Monitor because the Arduino UNO R4 cannot do any tasks during a delay. As a result, it misses detecting those presses.

Arduino UNO R4 Code - Without Delay

/* * This Arduino UNO R4 code was developed by newbiely.com * * This Arduino UNO R4 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-uno-r4/arduino-uno-r4-blink-led-without-delay */ #define LED_PIN 3 // The Arduino UNO R4 pin connected to the LED #define BUTTON_PIN 7 // The Arduino UNO R4 pin connected to the button #define BLINK_INTERVAL 1000 // interval at which to blink LED (milliseconds) int led_state = LOW; // led_state used to set the LED int prev_button_state = LOW; // will store last time button was updated unsigned long prev_millis = 0; // will store last time LED 1 was updated void setup() { Serial.begin(9600); // set the digital pin as output: pinMode(LED_PIN, OUTPUT); // set the digital pin as an input: pinMode(BUTTON_PIN, INPUT_PULLUP); } void loop() { unsigned long current_millis = millis(); // check to see if it's time to blink the LED 1 if (current_millis - prev_millis >= BLINK_INTERVAL) { // if the LED is off turn it on and vice-versa: led_state = (led_state == LOW) ? HIGH : LOW; // set the LED with the led_state of the variable: digitalWrite(LED_PIN, led_state); // save the last time you blinked the LED prev_millis = current_millis; } // check button state's change int button_state = digitalRead(BUTTON_PIN); if (button_state != prev_button_state) { // print out the state of the button: Serial.println(button_state); // save the last state of button prev_button_state = button_state; } // DO OTHER WORKS HERE }

Detailed Instructions

Follow these instructions step by step:

  • Upload the provided code to Arduino Uno R4
  • Press the button four times.
  • Observe the LED: It switches between ON and OFF every second.
  • Check the output on the Serial Monitor.
COM6
Send
1 0 1 0 1 0 1 0
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
  • All button presses were detected.

Code Explanation

The explanation is in the comments section of the Arduino code above.

Adding More Tasks

This code makes two LEDs blink at different times and also checks if a button is pressed.

/* * This Arduino UNO R4 code was developed by newbiely.com * * This Arduino UNO R4 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-uno-r4/arduino-uno-r4-blink-led-without-delay */ #define LED_PIN_1 3 // The Arduino UNO R4 pin connected to the LED 1 #define LED_PIN_2 4 // The Arduino UNO R4 pin connected to the LED 2 #define BUTTON_PIN 7 // The Arduino UNO R4 pin connected to the button #define BLINK_INTERVAL_1 1000 // interval at which to blink LED 1 (milliseconds) #define BLINK_INTERVAL_2 500 // interval at which to blink LED 2 (milliseconds) int led_state_1 = LOW; // led_state used to set the LED 1 int led_state_2 = LOW; // led_state used to set the LED 2 int prev_button_state = LOW; // will store last time button was updated unsigned long prev_millis_1 = 0; // will store last time LED 1 was updated unsigned long prev_millis_2 = 0; // will store last time LED 2 was updated void setup() { Serial.begin(9600); // set the digital pin as output: pinMode(LED_PIN_1, OUTPUT); pinMode(LED_PIN_2, OUTPUT); // set the digital pin as an input: pinMode(BUTTON_PIN, INPUT_PULLUP); } void loop() { unsigned long current_millis = millis(); // check to see if it's time to blink the LED 1 if (current_millis - prev_millis_1 >= BLINK_INTERVAL_1) { // if the LED is off turn it on and vice-versa: led_state_1 = (led_state_1 == LOW) ? HIGH : LOW; // set the LED with the led_state of the variable: digitalWrite(LED_PIN_1, led_state_1); // save the last time you blinked the LED prev_millis_1 = current_millis; } // check to see if it's time to blink the LED 2 if (current_millis - prev_millis_2 >= BLINK_INTERVAL_2) { // if the LED is off turn it on and vice-versa: led_state_2 = (led_state_2 == LOW) ? HIGH : LOW; // set the LED with the led_state of the variable: digitalWrite(LED_PIN_2, led_state_2); // save the last time you blinked the LED prev_millis_2 = current_millis; } // check button state's change int button_state = digitalRead(BUTTON_PIN); if (button_state != prev_button_state) { // print out the state of the button: Serial.println(button_state); // save the last state of button prev_button_state = button_state; } // DO OTHER WORKS HERE }

Video Tutorial

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