Re: [avr-chat] avrdude-ATMega32 fuse bits issues

[Galen Seitz]

Terry Karlson <address@hidden> wrote:

> Hmmm...  let's try a quick calculation:
> 
> Take the common breadboard configuration of rows of 5 holes
> connected. Let's calculate the capacitance between 2 parallel rows and
> assume that figure at least indicates the scale of parasitic
> capacitances we're dealing with.
> 
> Yanked a row of contacts out of a breadboard: it's essentially 2 flat,
> parallel leaves (===== viewed from above), so between 2 rows we just
> have a parallel plate cap.  Separation ~ 0.5 mm.  Length of base = 12
> mm.  Now, the leaves within a row start out vertical at the base, but
> above 2 mm, deflect towards each other higher up, so here the
> separation between rows is greater than 0.5 mm (up to about 2.0 mm
> apart).  So, we could take the height as 2 mm and assume that accounts
> for most of the capacitance, but let's just double that to 4 mm just
> to be sure.  (The total height of the leaves is 7 mm.)  So, area ~ 12
> * 4 ~ 50 mm^2.
> 
> I'm not sure exactly what types of plastic breadboard blocks may be
> made of, but a glance at a table of relative permittivities eps{r}
> shows a few plastics in the range 2 .. 3, so take eps{r} ~ 3.
> 
> Thus, C = eps{r} eps{0} A / d ~ 3 * 9e-12 * 50e-6 / 0.5e-3 ~ 3 pF.
> 

Nice job.  In our EE labs at school we were told to use 5 pF for the
capacitance between rows.

galen