A simple app for an STM32 Nucleo-F030R8 board that produces a variable freqency tone in the audio range based on a potentiometer. Piezo speaker is driven with a differential square wave to get 6.6Vp-p.
Place a piezo speaker across PA6 and PB6, which are mapped to TIM16_CH1 and TIM16_CH1N.
Connect a potentiometer wiper at PA0, which is mapped to ADC1_IN0. Connect the ends of the potentiometer to CN7 pin 8 (GND) and pin 12 (3.3V).
The current frequency is output on the STLINK UART (38400,8N1) and udated every 100 ms.
The TIM16 and ADC1 drivers are hand-written.