I have been doing some software work on an open source hardware/software project that produces a video overlay, but also offers an apparent audio out pin that is so far unused. The original developer of the hardware is nowhere to be found, and no questions asked of him have been answered for almost a year.
The board (which has already been produced in quantity, so changing it is not an option currently) offers a hook to an apparent audio out line off PB7:
I would like to get a simple tone of variable pitch on this line. If it could be a smooth sine wave from the DAC, that would be best, but even a rough triangular or even square wave would be useful to the users of this board.
I am not a EE guy by trade, so the 2 hours I've put into researching this might not have been enough. If someone actually has relevant code that would be a lovely miracle, but just general directions for how I might be able to hook the components of the microprocessor together in code would be most welcome. Can I use one of the DACs? Am I limited because this is UART pin?
The alternate functions of PB7 are listed as TIM4_CH2, I2C1_SDA, USART1_RX, FSMC_NL, and DCMI_VSYNC. Are any of those functions useful for making audio?
TIM4 is apparently being used to count horizontal lines in the video:
// Line counter: Counts number of HSYNCS (from hsync_capture) and triggers output of first visible line
See line 274 here: https://github.com/StewLG/PlayuavOSD/blob/master/src/osdcore.c