Creating a Crystal Oscillator!

Hey there! Have you ever wondered you your computer keeps track of time throughout the day, even if you turn it off, disable wifi, and leave it for a month? Well, the answer is a simple, crystal oscillator circuit.

A sample crystal oscillator PCB.

Crystal oscillators typically use quartz crystals cut in different ways to produce resonating frequencies. This is because of the Piezoelectric effect, which is a phenomenon where certain crystals generate electrical charges at a frequency, depending how they’re cut. By supplying an initial voltage, we can apply a mechanical stress to the crystal, which will cause it’s electric charges to vibrate at a certain frequency. We can step this frequency down, to achieve a very stable 1 second pulse, which through some circuitry, can keep very accurate time.

To take advantage of this feature, we can design the Pierce Oscillator Circuit, which uses a NOT gate, combined with a circuit to constantly keep the crystal beating. This works by supplying voltage when the crystal is at its lowest point, thereby reinforcing it’s pulse.

A Pierce oscillator circuit schematic. The capacitors smooth out the pulses, while the Resistor enforces the pulse by forcing one side to have a HIGH, and the NOT gate keeps alternating the HIGH side.

I have been working on recreating this circuit, by using off-the-shelf components at M5. Due to the MOSFET’s amplification section, I can amplify the signals generated by the crystal.

A recreation of the Pierce Oscillating Circuit.

Now that I got this signal, I will be passing it through a chain of flip flop gates to divide the frequency into 1 second.