I bought several Arduino Pro Mini from different sources: Watterott, EXP-Tech (Adafruit reseller), and so on.
Most of them have a ceramic resonator, which I learned isn't that stable in respect to a constant clock
frequency (fingers crossed that this ad hoc english is enough understandable ... I am no native speaker).
But there is one, which resonator /looks like/ as it could be an Crystal resonator (quartz).
Unfortunately I have neither a BOM nor the schematics of that guy.
It is tight fit to the gorund (PCB) .
I can identify two soldering point but not knowing, whether there is third one right below (for example)
of the housing of it between PC and housing.
The resonator is HUGE in comparison to the ceramic ones and on it it is written:
TXC 8.000
(it is a 3.3V version).
Size of the housing: 1cmx3mmx4mm
Is there any way to determine what exactly it is?
Thank you very much for any help in advance!
Best regards,
mcc
The ceramic resonators are not nearly as good as a crystal - but they are good enough for serial and most other common tasks. Many of the official Arduino boards use a ceramic resonator, not a crystal.
A part marked TXC 8.000 is almost certainly a crystal, and that sure sounds like an 8mhz SMD crystal - post a pic to be sure (many of us, including me, can identify if it's a crystal on sight), but I don't think TXC makes the ceramic resonators... They're huge in the crystal business though!
If you need accurate timekeeping, you might want to look into an RTC module (depending on your needs).
which I learned isn't that stable in respect to a constant clock frequency
How much accuracy do you need?
You might just try an experiment... Maybe run them for 24 hours and count milliseconds and check how far off the milliseconds are.
If it has a metal housing it's probably a crystal. Crystals have two connections, although the case may be optionally grounded.
If you want time-of-day, an RTC (real time clock) module is usually tuned/trimmed for better accuracy than a crystal alone. And, an RTC module either has a built-in battery or a connection for a battery so it can maintain time if power to the Arduino is lost.
No clock is perfect and they all drift, except your computer or cell phone clock which gets its time from an atomic clock somewhere on the network.
thank you for all this help!!!
This is a very friendly forum by the way...but I dont want to bore you with things you may already know 8)
I found a photo on the internet (just googling) which displays a nearly identical Arduino as the one
I have:
(left one). The photo already says "crystal"....what do you think?
(I have no relation to that site other than finding it via google).
Accuracy:
I came the "the other way round":
If I can buy an Arduino Pro Mini with ceramic resonator and one with crystal resonator and both
costs me the same...which one should I take?...AHA!...you see... ?
RTC: Yes, I know of these ones...I experimented with a DS3234, but it eats my coin cells like hell.
That metal thing on the one one the left? That's a crystal alright, in HC/49 package.
Some of the RTC modules on the market have a design flaw and attempt to charge the coin cell battery while the board is powered, which damages the (non-rechargable) coin cells. I don't know which RTC chip the bad boards were based on, though, let alone whether you have them.
DrAzzy:
That metal thing on the one one the left? That's a crystal alright, in HC/49 package.
Some of the RTC modules on the market have a design flaw and attempt to charge the coin cell battery while the board is powered, which damages the (non-rechargable) coin cells. I don't know which RTC chip the bad boards were based on, though, let alone whether you have them.
