I recently put together one of the very cheap ($15) toy digital oscilloscope products from JYE Tech, the DSO150, see?
The main board comes fully assembled and tested, with an STM32, rotary encoder and attached colour TFT, circuit diagram at
Could this become a neat Morse Tutor with some work to the sketch and a little hardware in place of the supplied analog board?
73,
Bob GM4CID
