On Fri, 17 Aug 2012 21:45:44 -0400, Phil Hobbs
wrote:
Jeff Liebermann wrote:
On Fri, 17 Aug 2012 16:40:00 -0700 (PDT),
wrote:
I used only sunlight (Phoenix, AZ, 32N latitute, sky probably 90% clear),
and for EPROMS written with all 0s, over 90% of the bits would erase
in a day, 100% in 2 days, so I'd erase for 3-5 days.
In the late 1960's, I was working on a nifty new product that included
some of the first EPROMs. The prototype was done and the boss
declared that it was time to take a proper photograph for the product
release, manuals, promos, literature, etc. After the photographers
with their bright lights were done, I couldn't make it work. I
eventually determined that all the EPROMs had at least been partially
erased. My guess is about an hour under the very bright lights. I
didn't see the lights but suspect they could have been arc lamps as
incandescent lamps doesn't have enough UV content to erase EPROMs.
Installing a spare set of EPROMS got it working again. After that
experience, I made it a habit of putting labels over the EPROM window.
_Foil_ labels. Paper sometimes wasn't opaque enough.
Agreed. I still have a lifetime supply of 5 1/4" floppy disk write
protect tabs. Most are black vinyl(?) or some opaque black plastic
over paper. They go on easily, and remove without leaving a mess.
Incidentally, I just remmembered that I once won an arguement whether
a stick arc welder will erase an EPROM. An Intel 2764 was used
because I had plenty of them. My guess is that it takes about 2
minutes of exposure to trash the EPROM and about 10 minutes to totally
erase it. Keeping an arc going for 10 minutes was impossible, but 15
seconds at a time was easy enough. I also managed to get slag on
every EPROM, but that was expected.
When I tried to use some of the test EPROMs later, I found that I had
zapped some cells. I don't know how I did that since I shoved the
leads into a crumpled block of aluminum foil.
Assuming 200A at about 10V across the arc, that's 2000 watts. My wild
guess is about 1/10th of that is UV. Assuming a spherical radiation
pattern, a distance of about 10 cm, and an old EPROM chip size of 0.25
cm^2 chip area, the UV power density is very roughly:
Surface area of sphere =
4 Pi r^2 = 4 * 3.14 * 10cm^2 = 1256 cm^2
Power density
= 2000 watts / 1256 cm^2 / 0.25 * 1/10 = 0.64 watts/cm^2
That's 130 times the UV that's delivered by the typical 15mw EPROM
eraser. I would have expected it to erase the EPROM 130 times faster,
but that didn't happen.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558