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Author Topic: Sanguino Atmega 644p 16MHz Crystal 100nf caps  (Read 1304 times)
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hey guys & gals,

   I have a slight problem here. Last night I soldered together my own Sanguino board. I went with a real bare bones design. I'm using my authentic Atmel avrispmkii USB ICSP programmer.
 
  It all works great. I'm able to upload the basic "blink" sketch onto the chip via the Arduino IDE. There's one major problem. The LED blinks on and off about once every 16 seconds.... leading me to believe the chip is using its internal oscillator of 1MHz instead of the 16Mhz crystal in have installed.

  Sounds like a good theory right? I'm a little unsure though. I'm using some real cheapie crystals I bought from Ebay. The two caps I'm using are good caps, but they're labeled 104 ... which is 100nf instead of the 20-20pf that I should be using.

  Does anyone have experience with this? I'm almost positive it's just using the internal oscillator.

  I was about to test it by de-soldering a leg of the crystal to see if the led will still blink ... but wanted to wait until maybe someone could tell me what might be really happening.

here is what I have in boards.txt (inside my Sanguino folder)

avrispmkii.name=Sanguino w/mkii
avrispmkii.upload.protocol=avrispmkii
avrispmkii.upload.maximum_size=63488
avrispmkii.upload.speed=38400
avrispmkii.upload.using=avrispmkii
avrispmkii.bootloader.low_fuses=0xFF
avrispmkii.bootloader.high_fuses=0xDC
avrispmkii.bootloader.extended_fuses=0xFD
avrispmkii.bootloader.path=atmega644p
avrispmkii.bootloader.file=ATmegaBOOT_644P.hex
avrispmkii.bootloader.unlock_bits=0x3F
avrispmkii.bootloader.lock_bits=0x0F
avrispmkii.build.mcu=atmega644p
avrispmkii.build.f_cpu=16000000L
avrispmkii.build.core=arduino


thanks,
Phil
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Have you changed the fuses (using AVRDUDE)?
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good caps, but they're labeled 104 ... which is 100nf instead of the 20-20pf that I should be using.
Yes putting that value of cap on a crystal is killing it. I bet it works the same without the crystal.
So are you surprised using a capacitor 5000 times too big won't work.
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You need these (22pf) .. may also find on e-bay.

http://www.sparkfun.com/commerce/product_info.php?products_id=8571
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I had exactly the same speed problem with the 644 chip. Take a look here http://www.engbedded.com/fusecalc/

Edit: This is just for information, the caps are the problem here  smiley
« Last Edit: October 05, 2010, 04:38:41 pm by jabber » Logged

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  I haven't used avrdude at all to change fuses ... not really sure how.

Would it be necessary to change the fuses on a fresh chip purchased from Mouser?

  I ordered some 22pf caps. Will try it out as soon as I get them.



thanks,
Phil
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I haven't used avrdude at all to change fuses ... not really sure how.
Surely you jest.  I found a well written description with "avrdude fuses" and "I'm feeling lucky"...
http://www.google.com/search?q=avrdude+fuses&btnI

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Would it be necessary to change the fuses on a fresh chip purchased from Mouser?
1 MHz / internal oscillator is how they ship from the factory.
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  Thanks. I will try this asap.




Phil
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  Got my new caps in today an used AVRStudio 4 to set the fuses for an external Crystal. Works great now. Thanks.
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