The Pierce oscillator is a derivative of the Colpitts oscillator, and can be implemented using a minimum of components. Typically: a digital inverter, one resistor, two capacitors, and a crystal. The circuit I’m testing here is from KF5OBS,
which cuts this down even further by using a BJT in place of the digital inverter and taking advantage of the base-emitter capacitance to eliminate one capacitor
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub
