DAC Voltage Suddenly Unstable

[senorblasto]

I am sending voltage directly from the DAC on the Teensy to the Control Voltage Input on a analog voltage control oscillator.

The voltage was stable for months yet now the output voltage seems to be unstable.

Hardware: Teensy LC and Teensy 3.6

Circuit:

Teensy Synth

Ground ---> Ground
DAC Pin ----> CV Input

Issue occurs on both

Issue occurs with my original code along with the following simplified code.

I guess this instability could have always been there and I simply did not notice til now, but it seems to be new.

I will edit the post and post a picture of the signal on my oscilloscope as soon as I have it.

Is it expected that I send the DAC output through an opamp?

Or would using an opamp as a buffer simply output a buffered voltage with the same issue?

void setup() {
analogWriteResolution(12);
}

void loop() {
  for (int i =0; i < 4; i++){

   float dacU = i*1279.6875;
   dacU = round(dacU);
analogWrite(A21, dacU);
delay(2000);
}}

The voltage fluctuates noticeably at all times.

Thanks in advance

 

[senorblasto]

While taking a picture of the signal on an oscilloscope I realized that reading the signal without the ground connected to the scope looked the same as my issue....

The problem was fixed by connecting ground.

I was using my first ever self designed and printed PCB, looks like I have some grounding issues to fix.
I would delete this if I could, but I guess is good for others to see that people make stupid mistakes....

Use a multimeter FIRST before spending hours checking other things....

I am shocked that the voltage was able to effect the synthesizer and oscilloscope so much without a ground connected??!!

 

[fdaniels]

While you are fixing the pcb its a good idea to at least buffer the DACs output with a 740x adding a 68R at the output of the OpAmp. Its standard for Eurorack that every device protects itself as you cant be sure the other side is nice to your module....

 

[fdaniels]

While you are fixing the pcb its a good idea to at least buffer the DACs output with a 740x adding a 68R at the output of the OpAmp. Its standard for Eurorack that every device protects itself as you cant be sure the other side is nice to your module....

I am shocked that the voltage was able to effect the synthesizer and oscilloscope so much without a ground connected??!!

Its "grounded" via your Teensys USB connection