MiniSport Laptop Hacker 12

Published in

· 5 years ago

  

MiniSport Laptop Hacker - Vol 12, 6 Apr 1993 
Copyright(C) 1993 by Brian Mork. 

>>> PORTABLE POWER OPTIONS 
Twelve volt DC universality has again raised its head.  A number of peo- 
ple seem to be interested in running their computer from 12v DC, whether 
from the cigarette lighter or from portable batteries.  No problem!  The 
pinout (pinin?) of the power connector on the left side of the computer 
is very simple.  The Zenith manufactured power supply meant to plug into 
this connector is a switching power supply; be careful measuring its 
voltages, if you do that to compare with my numbers.  Switching power 
supplies only regulate voltages well when they're under load. 
  The round shield of the connector is ground.  It's more than a 
shield--it actually carries the return current.  It is electrically con- 
nected to the forward contact on the batter pack, becoming the BLACK pow- 
er line inside the computer. 
  The single smaller hole is a 5v DC (TTL) input that indicates when the 
AC adapter is being used.  If you're interested in running off a portable 
battery, leave this unconnected.  I'm not sure how (or if) this actually 
gets into the computer.  Apparently the battery pack itself has some cir- 
cuitry that requires the 5v signal. 
  The bottom of the two large holes is a 9v DC input providing power di- 
rectly to the computer.  This 9v doesn't electrically connect to the bat- 
tery pack at all.  It is mechanically routed to the center conductor on 
the bottom of the battery pack, becoming the RED power line soldered to 
the main CPU board inside. 
  The upper, rearward large hole is a 6v DC, used to recharge the battery 
pack.  Directly, or indirectly through a few components, it makes its way 
to the rearward contact of the battery pack and subsequently the YELLOW 
power lead inside the computer. 
  I claim ignorance on the inside of a battery pack.  Does anybody have a 
torn-open pack?  What exactly is the 5v signal used for?  Are there any 
compenents built into the pack or is it just batteries and wires? 
  In any case, I've had complete success running the computer from a 9v 
wall-wart transformer.  Large size paper clips happen to be exactly the 
correct size to make the 9v contact and rub in place next to the ground 
connection.  The Zenith power supply indicates that maximum of 2A is tak- 
en from the 9v supply.  Use an adjustable 3-terminal regulator to bring 
the 12v DC down to 9v.  If you're running straight from the cigarette 
lighter, put some huge inductance in line (a lamp ballast works fine) and 
a large capacitor on the car side of the inductor. A 1 amp diode put 
backwards (banded end toward the car side) will clamp any high voltage 
spikes from arcing into the connector if you pull the paper clip out, 
making the magnetic field of the inductor collapse. 

73, Brian Mork (Opus-OVH)          KA9SNF@wb7nnf.#spokn.wa.usa 
                                   Internet ka9snf@jupiter.spk.wa.us 
                                   6006-B Eaker, Fairchild, WA 99011