J
James Arthur
- Jan 1, 1970
- 0
That wasn't my battle plan. My idea was to have the polystyrene "platters"
simply there to have a place to glue the plates onto.
The plates themselves are on the INside of the disks with a thin sheet of
plastic (kitchen wrap, saran wrap, a sheet protector cut in half...) between
them. Something like this, and an ASCII artist I ain't:
@@ grommet through the center hole
******************* top cdrom disk
--------- brass shim stock glued to top disk
=================== thin plastic dielectric
--------- brass shim stock glued to bottom disk
******************* bottom cdrom disk
@@ grommet coming through from top
I calculate somewhere between 500 and 1000 pf for the capacitor with 3 mil
mylar and a 3 mil airgap allowance on both top and bottom plates.
I'm sort of curious why I was off nearly an order of magnitude from the
experimental results.
Jim
Your arrangement was clear, but my response to John wasn't. I was
fixated on the parasitics, and hence the capacitance of the
metallizations through two layers of CDROM material was what
interested me.
I measured this, and I get 133pF +/- 10pF. That's for two full-
circle aluminum-foil plates separated by two CDROMs.
So, you're not off. Neglecting airgaps, half-plates at 1/20th the
distance, through mylar, should give about 10x that value, or 1.3nF.
Best,
James Arthur