Detect button on a ground line (reverse eng)

Question

I've found a circuit board that has a couple of circuits (buttons, IR Receiver, LED, USB). The thing is that following the line for interfacing the buttons I came across what seems to be like buttons that are connected only to the ground line of the PCB while the other end is a free pin cable.

Is there a way for the arduino to detect the ground when the button is pressed or a way to detect a short of some kind? There is a smd and a resistor on both buttons.

Circuit:

Main Ground-----Button-----SMD Capacitor-----Resistor(101)-----Free Pin

Thanks in advance!

Edit: Circuit Board

Answer 1

Just connect the ground to the ground on the arduino, and the free pin to a IO pin. Enable the pull-up resistor on that pin using pinMode(<nr>, INPUT_PULLUP);. If the button is not pressed, you will read a HIGH. If the button is pressed you will read a LOW.

Answer 2

It sounds like you might have a PCB with debounced switches on them. One such circuit for debouncing switches looks like this:

That circuit and more about switch debouncing can be found here.

A debouncer basically masks the problem of switch "bounce" which is what happens when the contacts get close and the circuit is quickly closed and opened in rapid succession until a firm connection is obtained. Its a natural problem mechanical switches.

If that's not quite right, maybe you could help us help you better by posting a photo of the board in question.

Answer 3

I did some research on the subjects and I came with a solution: I borrowed the code from here and made some modifications to fit my needs.

const int buttonPin = 6;
const int buttonPin1 = 7;

int previousReading = HIGH;
int previousReading1 = HIGH; 

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(buttonPin1, INPUT_PULLUP);
  Serial.begin(9600); 
}

void loop() {
  int reading = digitalRead(buttonPin);
  int reading1 = digitalRead(buttonPin1);

  if (previousReading == HIGH && reading == LOW) {
     Serial.println(HIGH);         
  }

  if (previousReading1 == HIGH && reading1 == LOW) {
     Serial.println(LOW);
  }

  previousReading = reading;
  previousReading1 = reading1;

}