Analog pin interference T3.0

Hi Paul/Forum,

I've noticed some strange behavior of analogread. Changing the voltage at one pin influences the readout of the next pin being read.

The circuit consists of 4 potentiometers (104k) wired to analog pins 0 to 3. The graphs are made with Processing using a modified version of the sketch included in the teensyduino graph example.

First the teensy reads all 4 pins and you can see the effect of each potmeter on the next pin being read (the large value changes are of course me rotating the pots), with pin 3 affecting pin 0. But if I simply change the sketch to only read pins 0 and 2, using the same circuit, the same effect occurs. This time ignoring the pins not being read (with 0 affecting 2 and vice versa). This behavior occurs all the way to pin 9.

I doubt this behavior is normal and being a total newb I have probably tortured my T3.0 many times by making some wrong connections and also doing the teensyduino tutorials at 5V instead of 3.3V. Any clarification on this issue? Did I cripple my poor T3.0? Thanks in advance!

Code:
void setup()
{
  Serial.begin(9600);
}
void loop()
{
  Serial.print(analogRead(0));
  Serial.print(",");
  Serial.print(analogRead(1));
  Serial.print(",");
  Serial.print(analogRead(2));
  Serial.print(",");
  Serial.println(analogRead(3));
  delay(50);
}
Graph1.png
Code:
void setup()
{                
  Serial.begin(9600);
}
void loop()                     
{
  Serial.print(analogRead(0));
  Serial.print(",");
  Serial.println(analogRead(2));
  delay(50);
}
Graph2.png
 
Last edited:
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