Programmable multifrequency audio signal or sequence generator - produces security coded signal from memory in response to keying for acoustic transmission on telephone subscriber line

摘要

The generator generates audio tones simultaneously, or one after another, by a battery-powered IC enclosed in a rectangular housing (12), on the top of which are two input keys (14,16). Outputs from a loudspeaker on the underside of the housing are transmitted by an acoustic coupler into the mouthpiece of an analogue telephone set. The actual tones are determined by a code stored in a memory, and the emission from the loudspeaker is signalled by, e.g., an LED (26) adjacent to the keys. ADVANTAGE - Numerical code for identification of particular user can be transmitted easily without any requirement to memorise up to 10 digits in correct sequence.