setting output analog/digital pin to ground

Question

So I need to automaically eject a CD from a Blu-Ray drive, I have a wire welded on the drive's card that if manually connected for a split second (pulse) to the ground of that same card on the drive, will eject the CD. Now in order to do that automatically I'm using an Arduino Nano and I connected that wire to an analog pin "d1" set its mode to Output and connected the grounds of both Arduino and drive together. Here's my code 1

int ds1 = A2; //pin that indicates the existence of the CD inside the drive if HIGH and its inexistance otherwise
int d1 = A3;  //pin connected to the wire that if connected to ground ejects the CD

void setup() {
  Serial.begin(9600);
  pinMode(ds1, INPUT);
  pinMode(d1, OUTPUT);
  while((!analogRead(ds1))) //if the CD isn't inside the drive wait
  {}
}

void loop() {
  analogWrite(d1,0); //eject CD
  delay(500);
  while(!analogRead(ds1)) //if the CD isn't inside the drive wait
  {}
  delay(1000);
}

I'm thinking that maybe setting the pin to 0 doesn't necessarily mean I connected it to the gnd, it's just a possibility if you see anything wrong with the code or have any suggestion please help me

Answer 1

Yes, setting a pin to OUTPUT and setting it LOW effectively connects the pin to ground (via a few ohms of resistance).

There's a couple of things wrong with your code, though, which you should address:

• Use digitalWrite() not analogWrite().

analogWrite(pin, 0) is effectively the same as digitalWrite(pin, 0), but it's ambiguous to someone reading your code.

• You never "release" the pin, so once it goes LOW it stays LOW. You should emulate open drain by setting it to INPUT when not using it.

• You should get into the habit of putting repeated code into functions to make it more understandable what's going on.

For example:

void setup() {
  Serial.begin(9600);
  pinMode(ds1, INPUT);
  pinMode(d1, INPUT);
  waitForCD();
}

void loop() {
  triggerEject();
  waitForCD();
  delay(1000);
}

void triggerEject() {
  pinMode(d1, OUTPUT);
  digitalWrite(d1, LOW); // Press the button
  delay(100); // This is how long the button is pressed for
  pinMode(d1, INPUT); // Release the button
}

void waitForCD() {
  while(!analogRead(ds1)) //if the CD isn't inside the drive wait
  {}
}

• !analogRead(ds1) will only ever be true if the voltage at pin A2 is exactly zero volts. If you really want to read an analog voltage here you should find a threshold value that the value is compared to:

  while (analogRead(ds1) < 100)) {}

Or it may be that you actually want to use digitalRead()...