## Friday Free Board Quiz – the prize is A20-OLinuXino-LIME – Crystal Resonators Load Capacitors

A20-OLinuXino-LIME is our popular Linux OSHW computer.

You can win this board! To participate in the Quiz is enough to re-tweet the Twitter Quiz announcement message.

To double your chances you have to answer the Quiz question

The Quiz question is: How load capacittors are calculated for crystal resonator which operates in serirs resonance?

You have time to re-tweet and/or answer until Monday 29nd of February.

In Monday we will post the correct answer and ask random.org to generate random number in range then announce the winner and ship the board by post/airmail.

Good Luck!

1. inakizi
Feb 25, 2016 @ 22:02:59

It depends on the Load Capacitance of the Crystal to be used (CL) and the stray capacitance (Cs) of the PCB. Basically the series capacitance of the capacitors (C1 and C2) plus the stray capacitance must be equal to the Load Capacitance of the used crystal. So:

CL = (C1*C2)/(C1+C2) + Cs

So usually C1 and C2 are slightly lower than double CL.

2. bremenpl
Feb 26, 2016 @ 07:09:34

In series you dont use load caps.

Feb 26, 2016 @ 13:57:14

As per my knowledge, load capacitance is not defined for crystal resonator operating in series. It is taken as zero

Feb 26, 2016 @ 14:09:12

Load capacitor is not used in series resonant crystals

5. CL: load capacitance crystal
CI: capacitance of uC port
CP: capacitance of PCB wire

C1,2 = 2x (CL – CI – CP)

6. @Alex: That what I’ve seen in atmels SAM3S datasheets!

C = 2x (CL – CI – CP)

CP is mostly between 1 and 2 pF.
CI is somethimes not specified (p.e. old freescales).

PRO-TIPP: Use coolant spray (CRC 75) and a heatgun and test,test,test!

A few years ago I had a pcb which only works correctly in the summer month.. and I had used NPOs for the crystal!