piclist 2000\06\05\195846a >
Thread: Paralell port powered little device.
face BY : Mark Willis email (remove spam text)

I have seen more than one Parallel Port card modified such that the DB25
connector's pin 18 is re-defined as +5V (even one re-wired to have +12V
on there IIRC.)  IF you do that, document it WELL, hang a notice tag off
the card and off the printer cable, and still expect to some day have
problems (Fuse the +V line going into DB25 pin 18, ok?)

Try to cut down from 40mA, definitely, if you want to power off the
parallel port.  And check for patents on this (I know one local company
(?IQ Technologies?) had patented this same trick on Serial Ports.)  I'd
bet Parallel Technologies might have a patent here, if IQ Tech doesn't?
(Worked with both places somewhat.)  Not a problem for personal
non-profit use, though.  (It's been a while since then!)

Tricks here:  Have your PC-based code intentionally drive all of these
data lines high, as much as possible.  Siphon power off each of these
pins with a Schottky.  Cap right off those to supply power to the
device.  Obviously you have to do this intelligently...

With 8 pins, you can probably get ~4.6V while drawing 16-20 mA (as an
estimated upper limit.)  Use a plug-in Parallel Port card for this in
case you blow the card up.  Obviously, your protocol has to have room in
it for some of the data lines to be pulled up most of the time from the
PC side - Think "Pull all 8 lines high when in Idle state."  If you can
get by with less current, obviously you only need to pull the lines you
have diodes on, high.

Earlier PC ParPort's Data Out pins: 74LS374 octal latch, sources 2.6 mA
MAX, damaged if pulled low too hard.  Don't want to use a 10,000uF cap
on the other side of those Schottky's, 1uF or so is about it IIRC.  (it
HAS been a while.)

 2   D0          Data Bit 0
 3   D1          Data Bit 1
 4   D2          Data Bit 2
 5   D3          Data Bit 3
 6   D4          Data Bit 4
 7   D5          Data Bit 5
 8   D6          Data Bit 6
 9   D7          Data Bit 7

You cannot do too much with these, as they're OC Outputs (7405's
 1  /STROBE      Strobe
14  /AUTOFD      Autofeed
16  /INIT        Initialize
17  /SELIN       Select In

I'll second Arthur's idea - Joystick port will source quite a lot of
current (Ahem, it's NOT fused inside the PC, usually, and the smell of
smoking ribbon cable's NOT very nice, so be careful you wire it right.)

Keyboard port's also do-able (I'm about to put a laptop on my tech
bench, with an adapter inline with the keyboard cable.)  Buy a
polyswitch to replace the (usually 2A) keyboard picofuse WHEN you blow
it, ask if I can help you fix your laptop.  And I can find those fuses
if you cannot <G>

For information:
http://www.senet.com.au/~cpeacock/  has MOVED to
http://www.beyondlogic.org/ - that's Craig Peacock's pages, GOOD info,
take a look as it's better IMO than before
http://ftp.sunet.se/hwb/ for pinouts on most everything else, BTW <G>


Edson Brusque wrote:
{Quote hidden}

I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)

<393C3EA5.2B6A7F0C@foxinternet.net> 7bit

See also: www.piclist.com/techref/ios.htm?key=port
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