Teensy 3.6 DAC noise

[ffro]

Hi I m new to this forum, so please fogive me if the question is not well posed or as already been answered.
I m using a Teensy3.6 board to read data from an encoder and then write the estimated angular position to pin A21 using analogWrite.
I ve noticed a problem and I d like to know if it is a known behaviour and if there is any way to mitigate/solve it.
The problem is the following:

After 12h of working time the analog output started to be noisy (noise range +-0.2V) which make it unusable for the purpose.
I then tried to change the ouput pin from A21 to A22 and the noise is reduced to the original values (noise range +- 0.005V).

Since i only changed the output pin without altering the circuit i can assume the noise does not come from othersignals connected to the DAQ nor from the power supply.
Is there a way to solve the problem?

thanks in advance!

The connection layout is quite simple,
- Input TTL signal A+, B+ on digital pin 6 and 7
- Analog Output on pin A21 connected to a DAQ

The board is powered using 5V from a dedicated power supply.

i used the following script:

Encoder myEnc(6, 7);

const float MPI(3.14159265358979323846);
const int nSteps(4096*2);

void setup() {
  analogWriteResolution(12);
  Serial.begin(9600);
  Serial.println("Basic Encoder Test:");
}

long oldPosition  = -999;

void loop() {
  long newPosition = myEnc.read();
  if (newPosition != oldPosition) {
    float angleRad = 2.0*MPI*static_cast<double>(newPosition % nSteps ) / static_cast<double>(nSteps);
    if ( newPosition < 0 )  {
      angleRad += 2*MPI;
    }
    
    long analogAngle = (long)(angleRad/(2.0*MPI)*4096);
    analogWrite(A22, analogAngle);

    oldPosition = newPosition;
  }
}

 

[PaulStoffregen]

Very mysterious...

I d like to know if it is a known behaviour

I can't really give you an answer, other than this question, where I can say this definitely isn't a known behavior. I especially can't see any reason (regarding Teensy) why it would work well for 12 hours and then unexpectedly become noisy.

 

[jonr]

Does it occur if you get rid of all the encoder hardware and software? How about with a constant analogWrite() value?