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[on:]

Hello! I'm playing with IR receiver.. it is photo transistor. The problem is if I disconnect all (except usb) and look into Serial Monitor analogRead(A0) returning strange values (about ~200-300) but not 0. Why?

[Reply #1 on:]

the input is floating (definition of nothing connected) therefore does not have a defined voltage applied to it.

[Reply #2 on:]

Can you post your code and a schematic you use?

[Reply #3 on:]

no schema at all .. just arduino connected to usb ... code..

Code:

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}

void loop() {
  sensorValue = analogRead(A0);            
  Serial.print("sensor = " );
Serial.print(sensorValue);  
}

[Reply #4 on:]

If it only prints 0's it could be that the A0 line is grounded somehow. Can you check the other analog ports?

[Reply #5 on:]

how sensor is connected?

if sensor make ground connection when it got ir try with these two lines....

Code:

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
pinMode(A0, INPUT)
digitalWrite(A0, HIGH)
}

[Reply #6 on:]

The analog pin is not connected to anything and the pin mode is not set. The reading should float and be about good for a poor random number generator.

[Reply #7 on:]

Code:

pinMode(A0, INPUT)
digitalWrite(A0, HIGH)

Is no good because it makes the analogue input into a digital input and enables the internal pull up resistor.

See:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html
About floating inputs.