Understanding the 22pF Capacitors

I created these notes to help better understand the role of the components we are soldering on the MAKERbuino. They also contribute towards an understanding of the schematic. Please feel free to suggest changes.

The Two 22pF Capacitors

A capacitor is a component which stores charge. When voltage is applied to it, it charges up until it is ‘full’ of charge. During the charging phase, it appears at though current is passing through it because electrons are going into one side of it and coming out the other side. (This is just a result of the charging - the current is not actually flowing from one side to the other side). When voltage is no longer applied, the capacitor releases that charge and the electrons flow out the way they came in.

Many crystals require two capacitors of a specific capacitance to be connected to it in parallel in order to oscillate correctly. For this crystal, the specified capacitance is 22 picofarads for both capacitors. This must be obeyed for the pulse to be 16MHz. The reason the capacitors are required is an advanced topic well beyond the scope of this note. I’m not even sure I fully understand it yet after a few hours of reading! However a good starting point would be to read up on the ‘Pierce Oscillator’ circuit.