We need an external crystal (AKA resonator) to have the ATmega chip (Arduino’s brain) work. This crystal needs 2 capacitors (22pF or 30pF) connected to each electrode but there is a handy resonator which has built-in capacitors. You can find these from Digikey, Mouser, Sparkfun, or other electronics suppliers. From Digikey or Mouser, I would use search words as ‘resonator built in capacitor throughhole 16MHz’ for ATmega328 chip. This is what I found from Digikey.
This costs less than a dollar with built-in capacitor. That’s good, but only problem is the electrodes order. It’s pin#1-GND-pin#2 (pin # doesn’t matter). Why is this a problem? Look at the pin mapping diagram of the ATmega.
Pin numbers 8,9 and 10 on the ATmega168 (328 has the same arrangement) are GND, crystal #1, crystal#2, respectively. You see the problem? Yes, we can not simply plug in the resonator we found directly next to the corresponding pins of the chip. Some people use a large breadboard and long wires to connect the resonator to the chip. But I don’t like that. My goal is to make it compact. So I did a little modification to the resonator legs.
First, cut 3 of short (~15mm) 22 gauge wires and plug them into a breadboard.
Solder the resonator like this.
Trim excessive wires.
Finalize with insulating electrodes by a short heat shrink tube.
The assembled picture on a breadboard is shown below.