January 2017, summer holiday season down-under, afforded time to build something I’ve been wanting to build for several years, my first Digital VFO. I’ve built a kit Digital VFO with pre-soldered surface mount parts and burned-in firmware, but this was to be a scratch build with Arduino Nano, C code with modifications, and a Silicon Labs si5351 PLL clock generator on a breakout board. I used the wiring map and script from Tom AK2B (modified from one by SQ9NJE ) and uses Jason NT7S si5351 library. The script is simple, supporting a single push-button to cycle frequency increments, and dealing with encoder interrupts, contact debouncing, refreshing the LCD display, IF offset and VFO/BFO outputs. Jason’s si5351 library hides the gutsy device interfacing, giving you a handful of common-sense functions to call… for example, set_frequency() takes as its argument the frequency in centi-hertz (1/100th of a hertz) and the ‘clock 0/1/2’ flag. It couldn’t be simpler. The Adafruit board contains the si5351 and a 25MHz clock (from local IoT supplier Core Electronics). Here’s a video demonstration of the VFO’s features.