Not getting any output from ECG sensor AD8232 I am trying for the beginning to run a simple Arduino code in order to test the functionality of the ECG sensor. What I am getting on the output are some random values around 600 or around 200. 
I connected everything the same as in any tutorial about AD8232: 
GND -> GND, 3.3V -> 3.3V, L0+ -> digital pin 10, L0- -> digital pin 11, output -> analog pin A0. 
I placed the sensor pads on my body like in pictures (forming a triangle), but regardless of putting the electrodes or not, I always get the same floating signal.
Here is Arduino code:

int ecg;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(10,INPUT);
  pinMode(11,INPUT);

}

void loop() {
  if((digitalRead(10) == 1)||(digitalRead(11) == 1)){
    Serial.println('!');
  }
    else{
    // send the value of analog input 0:
    Serial.println(analogRead(A0));
    }
    //Wait for a bit to keep serial data from saturating
    delay(1);
}


When I run this code I get only "!" on the output, no matter where I put the electrodes on my body. When I comment "if" and "else" parts of the code and print directly only reading from the pin A0, I get those random floating values, like on the image.


I also tried another custom built ECG sensor, but the results are the same. I haven't found the solution anywhere. It is not about the noise, because when I touch the metal box of my PC, I only reduce the values but there is still nothing on the output.
The problem was that I connected GND on the other half of the protoboard and there was no connection. I thought that the whole length of the protoboard is on the same potential for + and -, so GND wasn't connected. After connecting GND pin correctly, all worked perfectly.