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Support Forum » Oscillator Datasheet

October 28, 2012
by jlaskowski
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I have not been able to find the datasheet for the oscillator that comes with the Nerdkit. Can you please provide a link to it? I think it would be nice to have it in the Members' "Downloads" section of your site with the other datasheets. Mine has "FS14.7P" enscribed on it, but I cannot find the datasheet Googling that.

Thanks. Jim

October 28, 2012
by Ralphxyz
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Well first you would have to look for a crystal not a oscillator.

But I am not sure you would find an actual datasheet.

Actually I just googled "crystal datasheet" and got some general returns on crystals in general. I am not sure if there are any specifics.

Possible if the manufacturer was know you might get some details.

Ralph

October 28, 2012
by jlaskowski
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I need the specific voltage requirements for the supplied oscillator.

October 28, 2012
by Noter
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The voltage requirements specified for the mcu are the limiting factor. If you have some other use for the crystal at other voltages you will probably just have to experiment and see if it works.

On the ATmega you can use the 14.7456MHz crystal in the 4v to 5v range. If you drop to 3.3v supply voltage for the ATmega the frequency must come down to 12MHz or less. These voltage/frequency requirements are found in the ATmega 168/328 spec. Often the internal 8MHz oscillator is selected for 3.3v operation.

October 29, 2012
by jlaskowski
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Thanks. If I remove the oscillator, will it automatically drop to 8MHz? Also, will the USB interface still work for programming?

October 29, 2012
by jlaskowski
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The question about the MCU dropping automatically to 8MHz if I remove the oscillator is still open, but I recall that the USB interface won't work at 3.3V anway, so the clock speed's effect on the USB interface is a non-issue.

October 29, 2012
by Noter
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To change from an external crystal to the internal oscillator requires setting the appropriate fuse values. The easiest way to change fuse values is with an ISP programmer but care must be taken because the reset pin and/or serial programming can be disabled and if that happens you will need a high voltage programmer to recover the chip.

If you change clock frequencies you will have to adjust all software timer based routines to use the new frequency. This is especially important for the serial I/O which is needed for programming with the bootloader. So your programs and the bootloader will have to be updated for the new frequency and loaded back on the chip. Or you could skip the bootloader and just use the ISP programmer to load your programs from now on.

The USB interface converts a USB signal from your PC to serial data at the mcu. If you check it with a meter you will see it's already 3.3v from the USB cable so it will continue to work at if you change the supply to 3.3v.

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