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Feed a perfect sinuois but not get a perfect one using the "passthrough" code.



I'm a newbie in real time DSP. I got my STM32H725G-DK and super excited for it.

I imported the "passthrough" to the IDE (STM32CubeIDE) and program the board.

As instructed, I connected the blue jack (LINE IN) to a sig. gen. generating a sinusoid at 10 kHz using Analog Discovery 2 (AD2) using a TRS-2-RCA (BNC) . Then, I connected the green jack (LINE OUT) to the scope (AD2) using a TRS-2-RCA (BNC).

The on-board display does not show the spectrum of the input sinusoid as expected.

The scope channel connected to the green jack (line out) does not show a good sinusoid.

0693W00000FDZIfQAP.jpg0693W00000FDZJ4QAP.jpg0693W00000FDZKvQAP.pngBlue is the input to the STM32H735 and the yellow is the one at the output of the board.

0693W00000FDZKqQAP.pngWhen, the frequency of the sinusoid decreses, e.g., 1kHz, the waveform at the output becomes a rectangular waveform?!?!


Here are some quantities that are good to know about the setup:

  • Board sampling frequency is set to 44100.
  • The frame rate of the on-board screen for computing spectrum is 2^13.

Any insight/solution to resolve this issue is very much obliged.

Chief II

As first your out is 10x then seems your signals on output overdrive amplifier = rectangle.

As second your ADC setup create LPF and 10kHz is overband. Try correct ADC sample time.