bin@primate.wisc.edu (Brain in Neutral) (05/22/89)
Do devices exist that can be put on a phone line to indicate whether the line is already in use? This would be used in a situation where two people in a home each have a modem, and one wants to know if the other is on, without picking up a phone to find out. All that would be necessary is a little thing with an LED. Thanks, Paul DuBois dubois@primate.wisc.edu rhesus!dubois bin@primate.wisc.edu rhesus!bin
dave@westmark.UUCP (Dave Levenson) (05/24/89)
Most modems are configureable for use on multi-line key telephone systems. When this option is selected, the modem closes a relay contact accross the second pair in its phone cord (the black-yellow pair if standard inside wire color-coding is followed on the RJ-11 jack). You can build a busy-lamp using a low DC voltage and a suitable indicator lamp switched by the black-yellow pair, and the indicator will be lit whenever either modem is off-hook. For example: |---| /--------------------------------> YELLOW 110 vac ====| |==== 10vac ~ |---| \------>|-----/\/\/\/----->|-----> BLACK ^ ^ | ^ ^ | | | | | | | transformer diode | resistor led | | 68k~ | | | | | V V to other indicators like the above: resistor + led -- Dave Levenson {uunet | rutgers | att}!westmark!dave ...the man in the mooney
bote@csense.UUCP (John Boteler) (05/26/89)
From article <298@indri.primate.wisc.edu>, by bin@primate.wisc.edu (Brain in Neutral): > Do devices exist that can be put on a phone line to indicate whether > the line is already in use? This would be used in a situation where > two people in a home each have a modem, and one wants to know if the > other is on, without picking up a phone to find out. There is a discussion in comp.dcom.telecom raging about this now. I came up with a different idea while reading your request, plus this has been used in a similar configuration before. Dig yourself up two relays, fairly small and cheap, which operate on ~5-10 volts and pull in with about 5-10 ma of current; you can find these at Radio Shack for maybe $5 US. Connect each relay's coil in series with the tip of each phone line. Connect each relay's normally closed contacts such that they interrupt the other line when the first phone is off-hook and drawing current through the relay. Now you won't possibly be able to use the other phone when the first is in use, and vice versa. Automatic exclusion key! -- Bote uunet!cyclops!csense!bote {mimsy,sundc}!{prometheus,hqda-ai}!media!cyclops!csense!bote