Sci.electronics FAQ
Telephone-related ASCII Schematics V1.01
Telephone in use light
Detecting a telephone RING
(manual) Phone In-Use Light
Phone to audio interface (SSI202 input)
Phone Off-Hook Indicator
'phone rang' indicator light
Phone Line to Audio
Phone in-use
Telephone Line Monitor (Plans)
Use old phones as an intercom
Phone-In-Use indicator
Telephone Power?
Hold function for Telephone
Digital/Standard Phone Line Tester
Sat Sep 10 17:07:20 2011 - permalink -
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http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem_Tel.html