Computer- based control system using telephone system standard tones
Ndungi, Fairrez Jacob Musembi
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Analogue signals can be converted to digital form at the source or destination depending on their characteristics, carrier media, transmission, and reception requirements. The Public Switched Telephone Network (PSTN) provides us with a communication grid spread across almost the whole world. Immense volumes of signals are carried through this network. These signals can be utilized for remote control through the telephone system at either end of the communication line. In this study, a Computer-based prototype system appropriate for controlling circuits and appliances miles away over the telephone system is presented. Personal Computer (PC) parallel port was configured, programmed, and used in achieving remote control over telephone system. Ring detection, Timing, Dual tone Multi-frequency (DTMF) Decoding, Switching and Interfacing Circuits are the key building blocks of the system. Software for control, scanning of input and interpretation, was developed using C++ high level programming language. The system was tested for compatibility by connecting it to PSTN. Reliability was tested by repeated use of the system from fixed and mobile lines for switching on and off lights and radio and TV systems. The system was effective in remote control of lights and appliances at home. Experimental results were achieved using a fluke PM3384A Auto-ranging Combiscope.