| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 2720.1 | sorry, only on older Macs | NUTELA::CHAD | Chad, ZKO Computer Resources | Fri Sep 13 1991 07:02 | 9 |
|
I believe the following to be true but make no guarantees:
Older Macs like the Mac plus, Mac 128k, 512k, etc had a
different serial port that used a 9pin connector, one of
whose pins had power.
Chad
|
| 2720.2 | Power is somewhere on the pins of later Macs too... | BENONI::ARNOLD | The profit is in the details... | Fri Sep 13 1991 11:12 | 13 |
| >>> I believe the following to be true but make no guarantees:
The Apple MIDI interface and the Altech MIDI interface both work on later
Macs (such as the SE) using the serial ports (modem or printer port).
Neither of these interfaces has an external supply of power or a battery
so they're getting their power from somewhere.
Could it be that power only shows up on the pins when the port is
`activated'? Keep trying. Alas, I don't have a pin layout for either
of the interfaces I own.
Good luck,
- John -
|
| 2720.3 | It's magic | RANGER::EIRIKUR | | Fri Sep 13 1991 11:51 | 7 |
| The Apple and the Altech are "parasitic" devices that do some magic to derive
power from the data lines. This seems to work fine as the MIDI interface
doesn't really need much current at all. There seems to be no problem with
these units. Apple should know what they are doing.
Eirikur
|
| 2720.4 | | KOBAL::DICKSON | | Fri Sep 13 1991 15:12 | 12 |
| Remember that among the data lines are some signals that stay "high"
all the time the circuit is in use (like Request-To-Send). If you only
need a small amount of power you could get it from there.
There is also a circuit called a "charge pump" that be used to convert
low voltages into high ones, or of different polarities, again as long
as you do not use much power.
ThunderWare sells a thing that plugs into the floppy port and steals
power for whatever was hoping to get it from the serial port. They
developed these for their scanners. I think they also sell one that
plugs into the wall power.
|
| 2720.5 | Where to find +5Vcc ? | AZUR::DESOZA | Jean-Pierre DE SOZA dtn 828-5559 | Mon Sep 16 1991 11:19 | 21 |
| I have consulted the Macintosh Family Hardware Guide (same format/
editor as I-M 1 to 6) and the pinout of the different connectors is
described. It depends a lot on the hardware you have.
- For those Macs that have a SCSI connector pin 25 provides with +5Vcc
but it is clearly noted that this should not be used for powering
any device, but only for connecting the termination resistors.
The supported current drain is NOT documented.
- For those Macs that have a diskette connector, pin 6 provides with
+5Vcc, 700 mA max, for powering a diskette drive.
10 1
[o\:::::::::/o] (as you see it on the back of the Mac)
19 11
- It's also possible to find +5Vcc on the mouse connector of a Mac
Plus, 20mA max (= useless), or on the ADB bus for the other Macs,
on pin 3 as far as I remember, with a usable current drain, 0.5 A or so.
_____
(4 o 3) (as you see in on the keyboard or on the back of
(2 1) a Mac)
---
I'm sure of the info about the disk drive and SCSI connector, but not
about the ADB bus, I've noted the first, not the 2nd.
|
| 2720.6 | power from Tx lines | COSMIC::DEVANE | | Mon Sep 23 1991 11:55 | 33 |
| I finally have an anwser to my original question. I'm now convinced
(%98) that some interfaces draw their power from the the transmit data
lines.
"Inside Macintosh" has the schematics for the modem and printer
interfaces on the Plus (I assume the SE, II, etc. are the same).
There are no power pins. There are no clever pullups to get +5V.
Only three signals drive out to the connector: Tx+, Tx-, and HSKo.
HSKo remains at a low voltage (~-4.6V) during MIDI operation (ie, when
I'm running the Master Tracks Pro demo) so it's not very useful for
generating a positive supply. That leaves Tx+ and Tx-.
I conjecture that Tx+ and Tx- could be rectified and filtered to
produce a small supply - a few mA @ ~3.5V. One kind soul (who wishes
to remain anonymous) looked inside their Passport interface for me and
thought they found diodes from the appropriate input pins to the power
supply node. That supports my conjecture. Though I haven't had the
opportunity to look inside an interface myself, I think I have come up
with a circuit that could run off this small supply. Now I just have
to build and test it.
If anyone would like to see the circuit if/when I get it working send
me mail. If there's enough interest I could post the schematic to the
archives.
Thanks everyone for the helpful suggestions,
ch
ps: this discussion only applies to newer Macs with the 8-pin mini DIN
connector; the older Macs with the 9-pin connector had both +5V and
+12V on the connector.
|