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From: "Thomas C. Sefranek"
Subject: Re: parasitic power
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Date: Wed, 08 Jan 2003 01:35:41 GMT
NNTP-Posting-Date: Tue, 07 Jan 2003 17:35:41 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Steve wrote in message
> I am looking for a way to tell my circuit that I have a PC connected to
> it by an rs232 (db-9) cable. All I really need is enough juice to turn
> on a 2N2222 transistor.
Well, what CURRENT will the 2222 be switching?
(This answer divided by the beta of the transistor dictates the base current
from the DTR line.)
> I thought about using parasitic power by reversing and rectifying the
> DTR and ground line. Because I am now using positive ground, I can no
> longer use ground as ground, correct?
Incorrect! Ground is common return for both polarities.
> The rs-232 cable will be going to
> a TI MAX3232CDR TTL to RS232 converter. If I am using positive ground,
> can this chip still detect the logic changes in the rs232 lines?
Ground has no effect.
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