From Newsgroup: comp.sys.cbm

Hi Daniel,

at the beginning of this thread you wrote and asked:

I've talked to Ed/WD [...], but according to him you
had said that one actually should use a 10 Ohm resistance
over the parallel part to be on the safe side. To me it
sounds to be a bit low. If one would use resistance to be
on the safe side, why then just use 10 Ohm, but maby it
makes sense to you or someone else in this group.

I think, this topic could be discussed a little bit more
and perhaps someone knows a VIA protection beside the extra
GND for the parallel cable (creating a ground loop).

Sometimes I heard of using resistors to e.g. protect the
C64's user port. But I personally never used resistors to
protect the Userport of one of my C64's, neither my parallel
cables.

And I _think_, that resistors are pretty useless against
overvoltages as discussed in the "extra GND line" branch of
this thread. To meet the requirements of the VIA chips, so
that it is able to detect a clear High or Low Level, the
resistors most probably would need to be less than 1KOhm.
These values have been estimated for logic levels around
0V to 5V. If you take overvoltages of +-220V into account,
these resistors wouldn't protect anything, because the
resulting current would be too high for the VIA again. Then
the general problem remains.


Is there anybody, who actually used resistors in his/her
hardware application and made positive/negative experiences
with them?


Womo

--- Synchronet 3.18b-Win32 NewsLink 1.113

From Newsgroup: comp.sys.cbm

Wolfgang Moser wrote:

A friend in electronics told me he quite amused after measuring his PC
LPT port to find out, the parallel logic was able to feed up to 10
amps, enough to keep a student cabin warm :-D

Ouch! My poor little VIAs...

I wonder where those 10 Ampere should come from. Must be a major design mistake in that particular PC.

OT: Let's see, if the following chip may help somebody to
construct some better sort of interfaces in the future
(Nicolas told me about)(would still need some additional
microcontroller to support the IEC and/or Commodore
parallel bus):

http://www.ftdichip.com/

And such an improved interface will cost at least three times as much as an XEP1541. I wonder who would buy such a device.

Nicolas

--

Email address is valid for replies (requires Re: in the subject) <--

- See my Commodore hardware projects at http://people.freenet.de/x1541 -
- Visit the German X1541 Shop at http://sta.c64.org/x1541shop_ger.html -

--- Synchronet 3.18b-Win32 NewsLink 1.113

From Newsgroup: comp.sys.cbm



Wolfgang Moser wrote:

That may help for some overvoltage conditions, but I'm not
able to get a proof, if it would protect against +-220V,
this would depend on the diode's breakdown (?) voltage.

At that voltage, you would blow the diode; you need a fuse to cut the line before the diode fries.

If you are worried about a spike conditions, then you need a choke.

Resistors work if they are sufficiently loaded at normal conditions; however they are generally two slow to react to small overvoltages.

I once had to debug a modem. It worked perfectly; it would respond to all AT commands, throw the relay, etc, but not dial out. I found out that it had been directly exposed to a lightning strike through the phone line. The two choke inductors that separated the jack from the circuitry were vaporized. Only a light silver metallic film remained on the board.



--- Synchronet 3.18b-Win32 NewsLink 1.113

From Newsgroup: comp.sys.cbm

"Axell" <Axell@nosp.rogers.com> wrote in message news:3F0CB60A.F74CA09E@nosp.rogers.com...

At that voltage, you would blow the diode; you need a fuse to cut the line before the diode fries.

or get a different diode. There are diodes used to protect aerospace electrical systems from direct lightning strikes, so I'm sure you can find
some geared for shunting off 220VAC. :)

--
White Flame (aka David Holz)
http://www.white-flame.com/
(spamblock in effect)


--- Synchronet 3.18b-Win32 NewsLink 1.113

From Newsgroup: comp.sys.cbm

or get a different diode. There are diodes used to protect aerospace electrical systems from direct lightning strikes,

A simple knot in the cable has been said to protect against lightning strikes as
well.

--- Synchronet 3.18b-Win32 NewsLink 1.113