Arduino button voltage versus HIGH/LOW state

Question

I'm measuring voltage between button's ground and input pole on the following sketch. When button is on off state, there's 5V there, when it's switched on and led turs on, there's 0. Is this a correct way, and also how do I make it easier to write code and have LOW represent led being off. In this sketch, digitalWrite(led1, LOW); means the LED is actually turned on, so how do I tweak this to be representative of actual state, high=led on.

#include <ezButton.h>
// -----
// Declaration
// -----
 
const int button1 = 9; 
const int led1 = 4; 
int ledState = LOW;
 
ezButton button(button1);
 
// -----
// Setup
// -----
void setup()
{
 
 pinMode(led1, OUTPUT); 
 pinMode(button1, INPUT_PULLUP); 
 button.setDebounceTime(50);
 
}
 
// *****
// Main Loop
// *****
void loop()
{
 if( digitalRead(button1) == LOW ) {
 digitalWrite(led1, HIGH);
 }
 else {
 digitalWrite(led1, LOW);
 } 
}
 
// *****

• Varonne: @Juraj but doesn't the "int ledState = LOW;" mandate that when starting up the Arduino with this sketch led is off?
• jsotola: what is the purpose of int ledState = LOW;? ... your program does not use ledState
• chrisl: So, if I correctly understand, you are getting confused, because turning the LED on means writing LOW to it. And you want to change that to not be confused anymore. Is that correct?
• lurker: To answer your question, Is this a correct way, yes, it is one correct way. There's nothing incorrect about an LED circuit that turns the LED on when the voltage is low, and off when the voltage is high. If you want to change that fundamental property, you have to change the circuit.
• DataFiddler: If I correctly understand, you're rather confused by the inverse logic of a PULLUP button. Alternatively to @Abel's comment you might define const int PRESSED=LOW; and write if (digitalRead(button1) == PRESSED) digitalWrite(led1, HIGH);

Answer 1

To answer the posted question literally: Yes, it is the correct way for your circuit, which has the button between the pin and GND, and the LED between VCC and the pin:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

I can understand the confusion. However, the meaning is right, because the level on the button's pin is LOW if pressed. And the level on the LED's pin needs to be LOW for current to flow.

You can define your own constants:

// other stuff left out
const int LED_ON = LOW;
const int LED_OFF = HIGH;
const int BUTTON_PRESSED = LOW;
const int BUTTON_RELEASED = HIGH;
void loop()
{
 if (digitalRead(button1) == BUTTON_PRESSED) {
 digitalWrite(led1, LED_OFF);
 }
 else {
 digitalWrite(led1, LED_ON);
 }
}

---

If you want to keep using HIGH and LOW, but interpret them as:

• HIGH = button pressed / LED on
• LOW = button released / LED off

Then you need to modify the circuit:

schematic

^{simulate this circuit}

Unfortunately, there is no pin mode INPUT_PULLDOWN for the button pin, so you need to provide the pull down resistor externally. Make sure to set the pin to INPUT, not INPUT_PULLUP.

A common value for the pull down resistor is 10 kΩ.