The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: "Jeff Verive"
Subject: Re: parasitic power
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Tue, 21 Jan 2003 16:57:37 -0600
NNTP-Posting-Date: Tue, 21 Jan 2003 16:57:38 CST
Word of advice: opto-isolator! Unless you want your PC's power supply to
fry your circuit (or vice versa), always interface with an opto-isolator.
You can get some that operate at less than a couple of milliamps - a piece
of cake for most serial ports.
"Thomas C. Sefranek" wrote in message
> Steve wrote in message
> > hello:
> > 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
> 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.
> > steve
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup