# How does this buzzer volume regulation work?

I've found a usage of a buzzer with volume regulation that I hadn't seen before.

Here's the schematic:

Timers PWM are activated like this (Atmel MCU) :

//off
PORTC.DIRCLR = 0b11110000;

//4k7 + 1k
//Enable Timer B/C
PORTC.DIRCLR = 0b01100000;
PORTC.DIRSET = 0b10010000;

//4k7
//Enable Timer A/C
PORTC.DIRCLR = 0b10100000;
PORTC.DIRSET = 0b01010000;

//1k
//Enable Timer B/D
PORTC.DIRCLR = 0b01010000;
PORTC.DIRSET = 0b10100000;

//0k
//Enable Timer B/C
PORTC.DIRCLR = 0b10010000;
PORTC.DIRSET = 0b01100000;


I've cut the complete code since I'm interested only on electrical side.

Can you explain to me how current flows through it to allow volume regulation?

What is not clear to me is that any way I enable or disable pins (GND or VCC), the current should always flow through lines without resistors and will not allow to power BUZZ in other configurations than:

• PWM3 +
• PWM2 +
• PWM0 -
• PWM1 -

Maybe I didn't understand the purpose C9 or buzzer principles.

• Looks like a capacitance piezoelectric resonator tuned with C and 4 ports to inject different signals 2 of them attenuated. Mar 25 at 13:45
• a poor man 2 bit DAC, maybe? Mar 25 at 15:19