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Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!psivax!al
From: al@psivax.UUCP (Al Schwartz)
Newsgroups: net.analog
Subject: Re: Any 555 mavens or PUT weenies out there?
Message-ID: <396@psivax.UUCP>
Date: Fri, 12-Apr-85 21:05:35 EST
Article-I.D.: psivax.396
Posted: Fri Apr 12 21:05:35 1985
Date-Received: Sun, 14-Apr-85 04:01:40 EST
References: <469@umd5.UUCP>
Reply-To: al@psivax.UUCP (Al Schwartz)
Organization: Pacesetter Systems Inc., Sylmar, CA
Lines: 23
Summary: 

In article <469@umd5.UUCP> zben@umd5.UUCP (Ben Cranston) writes:
>The situation is that I want to build a bitbanger serial interface for my
>kid brother's Apple ][+ that plugs into the game port, which has several
>TTL inputs and outputs.  The problem is that the only power supply available
>on the game paddle connector is +5 - and I'd rather not kluge in the Apple's
>two 12 volt supplies on the unused pins or run more wires.  I need a nominal
>amount of + and - 12 for the TTL-RS232 converters (MC1488 or MC1489) and for
>some strapping for DTR type stuff.  Rather than build a separate plug into 
>the wall supply or run on (ick) batteries, I thought I could design a small
>DC-DC converter to run off the available +5 and produce these voltages.
>Ben Cranston  ...{seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben  zben@umd2.ARPA

You can run an RS232 with the voltages +5 and -5.  You already have the +5.
In order to make the -5 you need to get an Intersil 7660 (negative voltage
generator).  I have heard that this part is available at such places as
Radio Shack.  This chip and two capacitors is all that is required to generate
the -5 voltage.
-- 
                                      Al Schwartz
                                      Pacesetter Systems Inc., Sylmar, CA 
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