5 Volts from Mac Serial Ports?

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Article #1692

#1692

From: Kris Livingston
Date: Thu, 20 Jul 1989 15:32

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I am trying to design a board that plugs into the Printer or Modem port on
a Mac Plus or later, and I'd like to know how to get 5 volts from the port.
(Apple removed the 5 volt supply pin from the serial ports beginning with
the Mac Plus.)  Apple does it with their MIDI interface, and Farallon does
it with MacRecorder, so I know it can be done.  Do any of you EE-types know
exactly what is being done on the board that extracts 5 volts from the serial
ports?  Or is this all proprietary?  I'd really rather not have to use an 
external power supply!

As usual, email responses--if there's sufficient interest, I'll post a summary.
Thanks!

Kris Livingston   
krisl@hpindwa.hp.com

Disclaimer:  HP is oblivious to any opinions that I might have expressed above.

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!motcsd!hpda!hpcupt1!hpindwa!krisl
From: krisl@hpindwa.HP.COM (Kris Livingston)
Newsgroups: comp.sys.mac
Subject: 5 Volts from Mac Serial Ports?
Message-ID: <36400002@hpindwa.HP.COM>
Date: 20 Jul 89 15:32:32 GMT
Organization: Hewlett-Packard, Cupertino CA
Lines: 16