Line in use indicator.

[mdshunk]

Years ago I had a simple "line in use" indicator that just teed into the mod cable and would light a little red LED lamp when someone was using any phone on that line. Does anyone have a print or a link so that I can make such a device? Thanks.

[Jacksnap]

Md...,
Basically the voltage difference is what triggers the LED. Off hook voltage drops to about 10V or less versus 30V on. I found this link that is about is as simple as they come.
http://www.aaroncake.net/circuits/phonbusy.htm

Years ago I used to modify phones for the telemarketing groups but have not done this for years since now everything is electronic and has all the bells & whistles built-in for cheap.

[mdshunk]

Thanks Jack. This circuit rings a bell now.

[Ron]

If you search google or yahoo "telephone in use indicator", you'll find sites like below

http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem_Tel.html#ASCIISCHEMTEL_001

3/4 of the way down on the link below:
http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm#inuse.gif

http://www.techlib.com/electronics/telephone.html

$12 for the one below
http://www.gizmocity.com/iui.html

$4 for the one below
http://www.montek.com/catalog/item5741.htm

[Jacksnap]

Ron, you forgot to tell md.. that the $4 only lights up in 'french'... LOL

(and I'm half Canadian!)