about external crystals

[karlis]

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.

[Soeren]

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).

[joe61]

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

[karlis]

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

[Soeren]

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.

[karlis]

so its a goner, thanks for information