Vocalize Telephone Number - 02/03/94 EDN Design Ideas: The circuit in Fig 1 is a simple method of vocalizing the digit number of a telephone keypad, which, for someone visually impaired, provide as heLPFul voice confirmation. A 75T202 dual-tone multifrequency (DTMF]receiver decodes the Design by Shwang-Shi Bai,Chun-Shan Institute of Science and Technology, Lung-Tan, Taiwan Voice Scrambler/Descrambler - This is a single-inversion voice scrambler/descrambler. Though no longer useful for police scanners, it would be a fun project for a hobbyist. it was designed for use on a 9-volt battery, but by changing resistor values proportionately, it could be adapte __ Designed by Andrew R. Morris
Watch-Dog for Telephones - Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap misuse indications. Quite often they do not offer guaranteed...__ Electronics Projects for You
Watch-Dog for Telephones - Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap/misuse indications. Quite often they do not offer guaranteed protection against unauthor-ised operation. A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here. This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse. in addition it transmits a loud tone through the telephone lines to prevent further misuse. __
Wireless Telephone Bug - Here's a neat little project that will allow you to monitor your phone line as soon as your phone is off hook. You can use a regular FM broadcast band radio to monitor the conversation. Just remember, it __
Wireless Telephone Eavesdropper Electronic - The IR transmitter connects to a telephone circuit, and transmits both sides of all telephone conversations to any line-of-sight location, within 40 feet. No power is taken from the central office, as long as all phones remain on-hook. The current flows through the phone and back to the central office__ |