Quartz cristal SPK16.000G,who now the frequency tolerance?

I need to now the tolerance,to accurate my stopwatch.

I have no idea what your talking about. Post a link or a datasheet.

I'm looking the datasheet of this quartz.

zainimechanical: I need to now the tolerance,to accurate my stopwatch.

So provide a link to the datasheet for the specific manufacture.

Most crystal resonators are in the 20ppm accuracy range but that is assuming you have matched the proper loading caps specified by the manufacture.

I think I know what the OP is talking about . The part number he quoted is the part number engraved on the top of the crystal on an official arduino UNO. Apparently he has a stopwatch sketch running (or plans to run one) and wants to know the accuracy. I found this post with a Google search of that part number: http://forums.adafruit.com/viewtopic.php?f=25&p=121801

I assume the oscillator is some division of the clock crystal, which says SPK16.000G on the top - presumably 16 Mhz. The hardware says Arduino UNO, board model R2.

Using the above method above I can get +/- 1 second every four days. Maybe better if I kept refining the TIME_CORRECTION value. But I think JChristensen is right - without temperature compensation (e.g. Chronodot) that's about the best I can do.

I agree Westfw - an amazingly small error is unacceptable in a clock application! A mechanical watch that's banged around and encounters large temperature variations keeps time as well as this.

raschemmel: I think I know what the OP is talking about . The part number he quoted is the part number engraved on the top of the crystal on an official arduino UNO. Apparently he has a stopwatch sketch running (or plans to run one) and wants to know the accuracy. I found this post with a Google search of that part number: http://forums.adafruit.com/viewtopic.php?f=25&p=121801

I assume the oscillator is some division of the clock crystal, which says SPK16.000G on the top - presumably 16 Mhz. The hardware says Arduino UNO, board model R2.

Using the above method above I can get +/- 1 second every four days. Maybe better if I kept refining the TIME_CORRECTION value. But I think JChristensen is right - without temperature compensation (e.g. Chronodot) that's about the best I can do.

I agree Westfw - an amazingly small error is unacceptable in a clock application! A mechanical watch that's banged around and encounters large temperature variations keeps time as well as this.

Well the crystal resonator on a Uno does not clock the 328p chip but rather the USB serial converter chip. The 328p uses a ceramic resonator, which has poorer accuracy specifications then a typical crystal resonator, maybe in the 200ppm range.

@OP ,
There you go. The crystal part number in your post title has nothing at all to do with the accuracy of the arduino processor.
Ok ? (understand ? (yes/no)

Hahaha...thank guy.good information,much understand. I have info to share spk16.000G not in datasheets,SPK it's the manufacturer,but from the webite,I can't find the datasheets about this quartz crystal. From other sources of quartz crystal manufacturers ,the lower ppm for quartz crystal is 10ppm frequency tolerance. That good to build oscilator for timing like microsecond stopwatch,but if you want more accurate timing,better we use OCXO(oven contro crystal oscillator) and more expensive oscillator rubidium atomic clock.

I am not sure you understood the information. That crystal has nothing to do with the arduino ,period. It is the for the USB communication timing.

Well, with some really lateral thinking, you could set the 16U2 up as a timebase at say, 10 Hz, sending that reference into pin 0 of the 328 and let the 328 do the counting.

how?

PB4-5-6-7 on the 16U2 are brought out to pads, yes? Same with PB2-3-4.

PB7 can be a PWM output - so program it for 10 Hz, 100Hz, whatever is convenient for time keeping:

OC0A/OC1C/PCINT7, Bit 7 OC0A, Output Compare Match A output: The PB7 pin can serve as an external output for the Timer/Counter0 Output Compare. The pin has to be configured as an output (DDB7 set “one”) to serve this function. The OC0A pin is also the output pin for the PWM mode timer function. OC1C, Output Compare Match C output: The PB7 pin can serve as an external output for the Timer/Counter1 Output Compare C. The pin has to be configured as an output (DDB7 set “one”) to serve this function. The OC1C pin is also the output pin for the PWM mode timer function. PCINT7, Pin Change Interrupt source 7: The PB7 pin can serve as an external interrupt source.

Any new or modified source code compilation for the 16U2 would have to be done outside the normal IDE environment, wouldn't it? That's not something for less then guru type programmers, is it?

That's not something for less then guru type programmers, is it?

You mean like me ? XD

People reprogram the 16U2 for HID interfaces & stuff, yes?
Turning on a PWM output wouldn’t seem that difficult.
Maybe add to this file that is included in the IDE, do the makefile stuff, reload it via the 16U2 ICSP header.

Arduino-usbserial.c (8.25 KB)

CrossRoads: People reprogram the 16U2 for HID interfaces & stuff, yes? Turning on a PWM output wouldn't seem that difficult. Maybe add to this file that is included in the IDE, do the makefile stuff, reload it via the 16U2 ICSP header.

That is my point, when you get to using makefile and compilation, linking, etc, all outside the standard IDE you are definitely talking programmer guru territory. I certainly can't do it even after >5 years of arduino experience, and I suspect you don't have the needed knowledge and experience also? We both know it can be done, but would have little luck explaining to the OP how he can accomplish it?

There's a readme.txt in the same folder, along with a make file. Looks like it's figure-out-able.

If you can explain to me how it can be done, I can explain it to the OP. I have experience training people from scratch.