Crystal preparation

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.


16MHz resonator with capacitors
16MHz resonator with capacitors

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.


ATmega168 pin map
ATmega168(328) pin map

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.

Xtal soldered

Trim excessive wires.

Finalize with insulating electrodes by a short heat shrink tube.

Xtal with heat shrink tube


The assembled picture on a breadboard is shown below.



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