A simple shield for a 3-channel generator with an OLED display.
Encoder change the current bit. A short press of the encoder button moves the current bit. A long press toggles the current generator. When switching, the frequency is recorded in EEPROM and is not reset when turned off.
A schematic diagram of a device with a printed circuit board is located - https://easyeda.com/UN7FGO/SI5351_OLED_SHIELD
You can also use this version of the generator - https://easyeda.com/UN7FGO/ARDUINO_SI5351_OLED_VFO
A brief description of the project can be read here - http://un7fgo.gengen.ru/?p=2084 (sorry, only in Russian).