Arduino Pullup

When using Arduino, we often use push buttons to trigger certain actions. To read the state of a push button, we need to connect it to a digital input pin of an Arduino. However, sometimes we might encounter a problem of intermittent button readings due to electrical noise or other factors. This is where a pull-up resistor comes in handy.

By using a pull-up resistor, we can ensure a stable and known state for the input pin when the button is not pressed. This is achieved by connecting one end of the resistor to the 5V power supply and the other end to the input pin, with the button connected between the input pin and ground. When the button is not pressed, the resistor keeps the input pin at a HIGH state.

Internal Pull-up Resistors

Arduino boards have built-in pull-up resistors that can be enabled in software. These resistors are connected between the digital input pin and the 5V power supply inside the microcontroller. By setting the pinMode of the input pin to INPUT_PULLUP, we can activate the internal pull-up resistor.

Here's a code snippet that shows how to enable the internal pull-up resistor:

const int buttonPin = 2;
int buttonState = 0;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  buttonState = digitalRead(buttonPin);
  Serial.println(buttonState);
  delay(100);
}

In this example, we define an integer variable buttonPin that holds the digital input pin number where the button is connected. We also define another integer variable buttonState that we use to read the state of the button. In the setup() function, we set the buttonPin to INPUT_PULLUP mode. In the loop() function, we read the state of the button using the digitalRead() function and print it to the serial monitor.

External Pull-up Resistors

In some cases, we might need a stronger pull-up resistor than the internal one. In that case, we can use an external pull-up resistor. The value of the resistor depends on the specific requirements of the circuit. A typical value for pull-up resistors is between 4.7kΩ and 10kΩ.

Here's an example circuit diagram showing how to use an external pull-up resistor:

In this example, we use a 10kΩ resistor as a pull-up resistor. One end of the resistor is connected to the 5V power supply, while the other end is connected to the input pin where the button is connected. The button is connected between the input pin and ground. When the button is not pressed, the input pin is pulled up to a HIGH state by the pull-up resistor.

Conclusion

In conclusion, pull-up resistors are useful when working with push buttons or other digital inputs. They help to ensure a stable and known state for the input pin, even in the presence of electrical noise or other factors. Arduino boards have built-in pull-up resistors that can be enabled in software, and external pull-up resistors can also be used when needed. The specific value of the pull-up resistor depends on the specific requirements of the circuit.