Sorry, I forgot to mention the load capacitance for those $0.10 crystals from Tayda.? They are spec'd on the website at 16 pF.
I have absolutely no idea (or any way to measure) the actual load capacitance presented to the crystal from the circuit in the T4.1 Raduino so please don't take me to task on that one - LOL.
Jim - W0EB
------ Original Message ------
Sent: 5/17/2021 6:12:00 PM
Subject: Re: [BITX20] Capacitance of the master crystal of the Arduino
My measurements have been more like 4 kHz off, 150 kHz off is a major major error.
On May 17, 2021, at 18:34, Jerry Gaffke via groups.io <jgaffke@...> wrote:
?You're right, 10pf is the max value, not 8pf.
Probably best to set it to 10pf.
My understanding is that the load capacitance setting has nothing much to do with startup drift.
Only with the final parallel resonant frequency when the crystal is placed in a circuit.
These crystals are intended for a circuit with more parallel capacitance than we have,
so in our circuit it operates at about 25.150mhz instead of 25.000mhz.
But that's ok, it gets calibrated out.
Setting it for the minimum capacitance value of 5pF would cause it to operate at an even?
higher frequency.??
I would like to know if I am wrong about this startup drift thing.
Jerry, KE7ER
On Mon, May 17, 2021 at 02:54 PM, Jim Sheldon wrote:
Thanks Jerry,
You beat me to the explanation. ?The OP mentioned a menu routine we (TSW) had in some of our early firmware but we removed it after we discovered it essentially made no difference. ?We just set it to a compromise 10pF and left it there. ?
?
Start up drift is so minimal it isn¡¯t even worth spending time messing with it.
?
Jim, W0EB
TSW Project Coordinator
Jim Sheldon