[time-nuts] Rb Oscillator - rather fundamental question

Matthew Smith matt at smiffytech.com
Wed Feb 24 08:45:08 UTC 2010


Quoth Kasper Pedersen at 24/02/10 17:44...
> It will.
> Set the fuses as you would have for a 10MHz crystal, and capacitively 
> couple the source to XTAL1. Leave XTAL2 open.
> Do not set the fuses for 'external clock mode'.
> 
> Do put something like 100pF+1k Ohm in series with the input. While they 
> won't promise anything, I have deliberately run 1A into the protection 
> diodes of an ATMega16 for many seconds and still had a functional part.

Many thanks.  I was wondering about doing this; Chris Keuthe quoted the 
figures from the datasheet but then I thought that this would be the 
ratings for an external oscillator, as surely an actual crystal would be 
putting out a much smaller voltage than those quoted.  A few days ago, 
on another list, David had suggested something similar with "faking" a 
crystal for an AT90S8535 RTC.

I also wondered how an AVR could not work when PICs are reported to.

I will certainly use the series R+C as you and David have suggested, but 
will not worry about further protection - the AVR is one of the cheapest 
components in the whole system - I am far more concerned about damaging 
the Rb module than the AVR!

Thanks to all who have answered on this.  I will post a link to details 
when I get this project up and running.

Cheers

M

-- 
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business:      http://www.smiffytech.com/
Blog/personal: http://www.smiffysplace.com/
LinkedIn:      http://www.linkedin.com/in/smiffy
Skype:         msmiffy
Twitter:       @smiffy



More information about the time-nuts mailing list