Currently I am working on a project with a stm32f302c8t6 mcu which I monitor an analog signal. I generate a tone using dac when the signal exceeds a certain treshold. My problem is that as soon as I generate the audio the analog signal path is interferred by the audio signal. The audio is output with a buzzer. At first I thought that the current drawn by the buzzer might be the reason.


simulate this circuit – Schematic created using CircuitLab

The dac output is a 440 Hz sinewave. I tried a seperate power supply with a dedicated 3.3v regulator for the audio section with a combination of several bypass capacitors with no success. Any recommendation will be highly appreciated.

  • 2
    \$\begingroup\$ Try replacing the buzzer with a fixed resistor that will allow the same amount of current to flow. If the noise goes away then you know that it is the buzzer itself that is the problem. If that's the case, please provide a link to the datasheet for the buzzer so we can get an idea of what it might be doing. \$\endgroup\$ – Elliot Alderson Jun 23 at 15:32
  • \$\begingroup\$ Please share type of the buzzer (or better: link to its datasheet) anyway. \$\endgroup\$ – Huisman Jun 23 at 20:46
  • \$\begingroup\$ Thank you for your responses.Datasheet of the buzzer is here img.ozdisan.com/ETicaret_Dosya/532541_6784614.pdf. I did try an 8 ohm speaker with the same result.I will try an equivalent resistor if available and inform about the result.The resonant frequency of the buzzer is 2800+-300 Hz.I also tried with the center frequency of 2800 Hz. \$\endgroup\$ – nouwon Jun 24 at 7:00
  • \$\begingroup\$ Problem persists with 10-20... up to 120 ohm resisitors.I am sure that this is a problem about power. \$\endgroup\$ – nouwon Jun 24 at 12:11

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