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From: ftpam1@acad3.fai.alaska.edu (MUNTS PHILLIP A)
Newsgroups: sci.electronics
Subject: Re: Help Needed: TTL<->RS232 without -12vdc
Keywords: RS232, TTL, level shifting
Message-ID: <1990Aug25.232127.4269@hayes.fai.alaska.edu>
Date: 25 Aug 90 23:21:27 GMT
References: <7574@scolex.sco.COM>
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In article <7574@scolex.sco.COM>, deanr@sco.COM (Dean Reece) writes...
> 
>Hi, I need some help with RS232 drivers/receivers
>I'm building a project that needs a standard RS232 port, but only has
>available supplies of +5, +12, and +24 volts.  I thought that I
>might be able to use the 0(GND), +12, and +24 kinda like the +/- 12v supply
>usually called for.  I couldn't think of any trivial way to do this,

     You could use a charge-pump inverter to generate -10V or so from the
+12V supply.  This takes as little as an LM555 and some discretes.  I just
use the MAX233 (MAX232 with integrated caps) myself.  If you're really lazy,
I once saw a data sheet for a DB25 connector with the MAX232 integrated.

Philip Munts N7AHL
NRA Extremist, etc.
University of Alaska, Fairbanks