Date: Sun, 27 Oct 2002 11:46:55 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: David Nicholas Kayal <davek@saturn5.com>, nbari@unixmexico.com, freebsd-hackers@FreeBSD.ORG Subject: Re: i am looking for a 5 volt signal Message-ID: <3DBC42AF.C68F31B0@mindspring.com> References: <Pine.BSF.4.44.0210270918380.364-100000@blackbox.yayproductions.com> <200210271919.g9RJJFEm091313@apollo.backplane.com>
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Matthew Dillon wrote: > Uh guys. Parallel port digital outputs do not generally have a whole > lot of drive. I really doubt a parallel port output could drive a > relay. Depends on the amperage the relay draws. 8-). I used to use the paralell port output to drive a pulse dialer and "off hook" for a modem that didn't have the capability itself (a 300 baud accoustic couple modem). One of the reasons I laugh when I see the "war dialer" scene in War Games. That said, you damn well better not draw any real current from the parallel port, if you want to avoid cooking it. In other words, do *not* use it to power something external, and if you are using it for a 1/0 signal to something that wangts to switch a lot of volts and amps from a real power supply, consider using an SCR, instead. > > And it's probably TTL level equivalents, not CMOS. Even if you ganged > the output bits together I doubt you would get enough drive out of > them. > > A serial port output (+/-12 but you may see +/-10 or -5 and +12 or other > out-of-spec combinations) is far more likely to be useful in driving > a relay, though again there will not be much drive. It would be far > better to supply the power you need from another source, like a +5V > power supply. Or just get a wallwart with DC output and run it through > a linear regulator. At least then you aren't likely to burn the house > down :-) Get a brick and use an SCR to switch the brick. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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