Power cable pinout

Tue, 9 Jul 91 15:46:32 edt

Here is the pinout diagram of the Ultralite's power cable. This is an end
view of the cable itself (I guessed a pin numbering scheme):

| ____V____ |
| / \ |
| / 7 1 2 \ |
| | | |
| | 6 [ ] 3 | |
| | | |
\ \ 5 4 / /
\ \_________/ /

Pin Function

1 Ground
2 Ground
3 [weird circuit -- see below]
4 Nominal +15V supply
5 Nominal +12V supply
6 Nominal +5V supply

Weird circuit (diode and NPN transistor):

3 __________________
7 --------->|-----|

We have no idea what the "weird circuit" is for.

The +15V supply is a current source for charging the molicel which
puts out about 80mA (.1C charging rate) and shuts off when the battery
voltage reaches a preset value -- this is why you can leave the supply
plugged in continuously without damaging the battery. The red charging LED
indicates when the current source is on.
I observe that the charging current is independent of the
Ultralite being on or off so it seems to me that the battery will charge
up equally well if the system is on or off.

The +12V source seems to supply main power in lieu of the internal

The battery itself has a 12V nominal voltage. My battery gets
charged up to 15V by the external supply, but this quickly drops to about
13.5V during the first few minutes of operation. At this battery voltage,
my Ultralite draws from 300 to 375 mA depending on the setting of the
backlight and CPU speed options -- switching to low speed saves about 25mA
(7%) and switching to low backlight saves about 50mA (13%).
I have noted down some battery voltages as the battery was dicharging but
I don't have them with me now. The low-battery light comes on at a voltage
of about 11.5V which, for me, is only the 30% charge point of the battery --
I can get another 1/2 hour or so of use after this point.
The battery is dead at about 10V -- at this point, the machine can't boot.

The +5V source seems to be used to run the floppy disk drive. At some
point we will try to figure out if this source is used at all inside the
Ultralite -- if not, then it may be possible to use an external 12V battery

The supply itself uses a switching circuit which regulates only the
+5V output (the actual voltages on the +12V and +15V being non-critical
since they are regulated elsewhere). The green power-on LED is driven by
the +5V output.

At some point I am going to try powering the beast from an external 12V
battery. I will let you know how this works out.

Bob (rca@rle-vlsi.mit.edu)