Tag Archives | pullup

Pushbutton Switch PullUp with digitalRead

This project involves a push-button switch that an Arduino UNO recognizes through code as necessary to activate an LED over a GPIO pin. Assembly of the circuit requires a 330 resistor, 10K resistor, normally open pushbutton switch, and a red LED plus some jumpers. For added clarity about the assembly refer to the photos below. The schematic illustration merely offers a symbolic representation of the setup.

Simple set up of a small circuit to interface with the Arduino UNO R3 SBC. Includes 330 ohm, 10K ohm current limiting resistors, a RED LED, and a small pushbutton normally open switch. Circuit jumpers interface to the Arduino’s GPIO ports.

To register active high and active low states at a GPIO port, it is necessary to apply pull up or pull-down resistors to a circuit’s normally open or normally closed pushbutton switch. It is not an acceptable practice to place a GPIO pin directly to a +5V source, or Ground in order to operate a directly connected switch. The purpose of a pulldown or pullup resistor placed onto a switch is to correctly register an active high or low state at an assigned GPIO measurement pin. To illustrate the connections see the diagrams below:

Simply put, there just must be a circuit path to either a voltage reference or ground reference using a resistor connected to a switch for proper operation. The active voltage present at pin-12, while the button switch is not pressed, is 5VDC. When the pushbutton switch is pressed this voltage level drops to 0VDC. As a 0VDC state is read into pin 12 by the digitalRead operation (i.e. pin 12 becomes grounded), pin 8 presents 5VDC to R2 for the Red LED to illuminate. These states correspond to the Sketch serial monitor “0” or “1” messages presented. While leaving the pushbutton switch unpressed, the serial monitor presents a digital “1” state. While the pushbutton switch is pressed and held closed, the serial monitor presents a digital “0” state. This is due to the placement of the digitalRead command within the continuous program loop.

To run the project it is necessary to assemble the circuit onto a breadboard using the components identified above. When the hardware is set up, it is then necessary to write and run the code to get functional use of the project.

Program & Functional Operation:

Code Setup:

int LEDPin=8;
int buttonPin=12;
int buttonRead;
int dt=250;

void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
pinMode(LEDPin, OUTPUT);
pinMode(buttonPin, INPUT);
}

void loop() {
// put your main code here, to run repeatedly:
buttonRead=digitalRead(buttonPin);
Serial.println(buttonRead);
delay(dt);
if(buttonRead==1){
digitalWrite(LEDPin, LOW);
}
if(buttonRead==0){
digitalWrite(LEDPin, HIGH);
}
}