Author Topic: about external crystals  (Read 992 times)

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Offline karlisTopic starter

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about external crystals
« on: August 28, 2011, 05:52:31 AM »
Hello.

Since i`m not a pro in electronics nor programming, and i`m willing to learn a lot in these areas, i`m wondering, if i realy need to connect external crystal to MCU ? Or it is needed only when i want to operate in higher frequency or in some specific frequency?

I have Atmega16 and Atmega8 wich is dead due fuse bit fail :(

My goal is to make a tank robot (have 4 360 deg. hacked servos) and in future tachometer for car.

Thans for your responses.

Offline Soeren

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Re: about external crystals
« Reply #1 on: August 28, 2011, 05:51:32 PM »
Hi,

[...] i`m wondering, if i realy need to connect external crystal to MCU ? Or it is needed only when i want to operate in higher frequency or in some specific frequency?

Some controllers need a crystal, others can (also) be run from an external RC oscillator with a timing accuracy of around 1%, if less accurate timing can be tolerated.

IOW If you're going to do anything time critical, like high speed comms, event timing or similar, you need a crystal. For most other jobs, the internal oscillator will be fine.

A 1% error is the equivalent of 14.4 minutes in 24 hours, so clearly the RC oscillator is a nogo for a time keeping job.


I have Atmega16 and Atmega8 wich is dead due fuse bit fail :(

How do you determine the cause to be brickin'?

Do you hope to bring them back?
If so, here's a couple of possibilities, but I'd personally use them as door stops and just get new ones, but of course, if you keep bricking them... If you've killed them in off any other way, there's no help in those.
http://www.mtcnet.net/~henryvm/4AvrFuseBuster/
http://www.der-hammer.info/hvprog/index_en.htm


My goal is to make a tank robot (have 4 360 deg. hacked servos) and in future tachometer for car.

You only need 1 servo/motor for a tank thread. With 2 motors, they will be battling each other if they're not exactly the same speed (and they never are).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline joe61

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Re: about external crystals
« Reply #2 on: August 28, 2011, 08:34:27 PM »
I have Atmega16 and Atmega8 wich is dead due fuse bit fail :(


In addition to the links Soren provided, there's a tutorial about recovering from bad fuse programming on the avrfreaks site http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=106325

I've used this info to recover a few mistakes with clock bits, for the others, I just ordered one of these, and I'm learning to be more careful :-)

http://mightyohm.com/blog/products/hv-rescue-shield-2-x/

Joe

Offline karlisTopic starter

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Re: about external crystals
« Reply #3 on: August 29, 2011, 12:11:36 AM »
Yes i would like to unbrick them some day, and i beleave i messed it up with wrong external clock fuse, but i have added a crystal befour that, i`ll try with bigger crystal, maybe it brtings it back from the dead :)

Thanks for your replies, they were realy helpfull

Offline Soeren

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Re: about external crystals
« Reply #4 on: August 29, 2011, 10:15:16 PM »
Hi,

[...] i`ll try with bigger crystal, maybe it brtings it back from the dead :)
The size of the X-tal won't change a thing.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline karlisTopic starter

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Re: about external crystals
« Reply #5 on: August 30, 2011, 11:29:52 AM »
so its a goner, thanks for information ;)

 


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