.. note:: Hello, welcome to the SunFounder Raspberry Pi & Arduino & ESP32 Enthusiasts Community on Facebook! Dive deeper into Raspberry Pi, Arduino, and ESP32 with fellow enthusiasts. **Why Join?** - **Expert Support**: Solve post-sale issues and technical challenges with help from our community and team. - **Learn & Share**: Exchange tips and tutorials to enhance your skills. - **Exclusive Previews**: Get early access to new product announcements and sneak peeks. - **Special Discounts**: Enjoy exclusive discounts on our newest products. - **Festive Promotions and Giveaways**: Take part in giveaways and holiday promotions. 👉 Ready to explore and create with us? Click [|link_sf_facebook|] and join today! Lesson 2 Controlling LED by Button ============================================ **Introduction** -------------------- In this experiment, we will learn how to turn on/off an LED by using an I/O port and a button. The "I/O port" refers to the INPUT and OUTPUT port. Here the INPUT port of the Uno board is used to read the output of an external device. Since the board itself has an LED (connected to Pin 13), you can use this LED to do this experiment for convenience. **Components** -------------------- .. image:: media_arduino/image171.png :width: 800 :align: center .. image:: media_arduino/image176.png :width: 800 :align: center **Experimental Principle** ------------------------------ **Button** ^^^^^^^^^^^^^ Buttons are a common component used to control electronic devices. They are usually used as switches to connect or break circuits. Although buttons come in a variety of sizes and shapes, the one used here is a 6mm mini-button as shown in the following pictures. Two pins on the left is connected, and the right is similar as the left, which is shown in the below: .. image:: media_arduino/image50.png :width: 400 :align: center The following is the internal structure of a button. The symbol on the right below is usually used to represent a button in circuits. .. image:: media_arduino/image205.png :width: 400 :align: center When the button is pressed, the 4 pins are connected, thus closing the circuit. **Principle:** ^^^^^^^^^^^^^^^^^ Connect one end of the buttons to pin 12 which connects with a pull-down resistor (to eliminate jitter and output a stable level when the button is working). Connect the other end of the resistor to GND and one of the pins at the other end of the button to 5V. When the button is pressed, pin 12 is 5V (HIGH), then pin 13 is set (integrated with an LED) as HIGH at the same time. If the button release, the pin 12 changes to LOW and pin 13 is set to LOW. So we will see the LED lights up and goes out alternately as the button is pressed and released. The schematic diagram： .. image:: media_arduino/image52.png :width: 800 :align: center **Experimental Procedures** ---------------------------------- **Step 1:** Build the circuit **Step 2:** Open the code file. **Step 3:** Select the **Board** and **Port.** **Step 4:** Upload the sketch to the board. .. image:: media_arduino/image228.png :align: center Now, press the button, and the LED on the Uno board will light up. .. image:: media_arduino/image229.png :align: center **Code** ------------------------ .. raw:: html **Code Analysis 2-1 Define variables** ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. code-block:: arduino const int buttonPin = 12; // the button connect to pin 12 const int ledPin = 13; // the led connect to pin13 int buttonState = 0; // variable for reading the pushbutton status Connect the button to pin 12. LED has been connected to pin 13. Define a variable *buttonState* to restore the state of the button. **Code Analysis 2-2 Set the input and output status of the pins** ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. code-block:: arduino pinMode(buttonPin, INPUT); // initialize thebuttonPin as input pinMode(ledPin, OUTPUT); // initialize the led pin as output We need to know the status of the button in this experiment, so here set the *buttonPin* as INPUT; to set HIGH/LOW of the LED, we set *LedPin* as OUTPUT. **Code Analysis 2-3** **Read the status of the button** ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. code-block:: arduino buttonState = digitalRead(buttonPin); buttonPin(Pin12) is a digital pin; here is to read the value of the button and store it in *buttonState*. **digitalRead (Pin)**: Reads the value from a specified digital pin, either HIGH or LOW. **Code Analysis 2-4 Turn on the LED when the button is pressed** ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. code-block:: arduino if (buttonState == HIGH ) { digitalWrite(ledPin, HIGH); // turn the led on } else { digitalWrite(ledPin, LOW); // turn the led off } In this part, when the **buttonState** is High level, write *ledPin* as High and the LED will be turned on. As one end of the button has been connected to 5V and the other end to pin 12, when the button is pressed, pin 12 is 5V (HIGH). And then determine with the *if*\ (conditional); if the conditional is true, then the LED will light up. *Else* means that when the if(conditional) is determined as false, run the code in *else*. **Experiment Summary** ------------------------ You can also change the code to: when the button is pressed, if (buttonState=HIGH). The LED goes out (digitalWrite(ledPin, LOW)). When the button is released (the else), the LED lights up ((digitalWrite(ledPin, HIGH)). You only need to replace the code in **if** with those in **else**.