cawapy
commented
7 months ago This is from the 5V voltage dropping by up to approx. 200 mV while the display controller/driver is multiplexing a digit with high number of segments lit.
2 cascaded inverters are used to drive the 2 buzzer lines from 1 sound signal created by the ESP32. The outputs of the inverters correspond to GND and 5V rails respectively. The buzzer "sees" 5V or -5V, which contains the ripple caused by the display controller/drivers which translates to noise directly.
This is a design flaw.
Options:
- Drive second inverter by another signal provided by the ESP. Then the software on ESP could make sure both buzzer lines see the same level when not playing any sound.
- Bind one of the buzzer lines to GND. Again, the software on ESP could then make sure the other line will be driven to same voltage when not playing any sound.
- Stabilize supply voltage of inverter
- Remove buzzer
- Place layers of scotch tape over buzzer's aperture ;-) yes it works! It reduces the buzzer's volume and the noise.
There is unwanted noise comming from the buzzer unless LEDs are off entirely. Depending on LED pattern shown, noise is more more or less intense. While it is way quieter than the buzzer's beep, the noise is unpleasant.