Date: Sun, 27 Oct 2002 15:50:05 -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: <3DBC7BAD.BCB59AD7@mindspring.com> References: <Pine.BSF.4.44.0210270918380.364-100000@blackbox.yayproductions.com> <200210271919.g9RJJFEm091313@apollo.backplane.com> <3DBC42AF.C68F31B0@mindspring.com> <200210272207.g9RM76sX091839@apollo.backplane.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Matthew Dillon wrote: > Huh. I would have expected you to use the current loop on the > phone line to power the dialer. There's a significant amount > of power available there, though you would have to isolate the > circuit since the common mode could be upwards of one or two > hundred volts. Telephone is 24 volts DC, which generally falls off to 18v at the customer permises. Ring is AC line voltage, to support mechanical ringers (e.g. 120v AC between ring, 24v DC between tip and ring). I worked as a lineman on private phone systems starting around age 14. 8-). > You could use an SCR but linear regulators are far, far better > (a little 3-pin TO92 package linear regulator). And linear regulators > have overcurrent protection as well (for themselves, not for whatever > is powering them). It's fairly difficult to blow one up. My SCR suggestion was based on the idea that you wanted to switch lots of volts/amps using Vcc chip levels to do it. THere are actually two threads here now: doing that, and lighting up a small number of LEDs (mention hardware projects, and the EE hobbiest wannabes come out of teh woodwork to ask for circuits... 8-)). Here is a good beginning parallel port project site: LED: http://www.free-hosting.lt/stech/lights/lights.htm Relay: http://www.armory.com/~rstevew/Public/Tutor/SolidStateRelaysDIY.txt Or a kit you can buy, with schematics: http://www.u-net.com/epr/electron/issue2/feat0302.htm Or more serious prebuilt stuff: http://www.lptek.com/io.htm And here is a wider selection, that has parallel port and serial port projects: http://ourworld.compuserve.com/homepages/Bill_Bowden/ ...and I'm disclaiming any responsibility, if you cook something with any of this... -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3DBC7BAD.BCB59AD7>