Abstract: An electronic diving apparatus detects pressure by means of a bellows transducer (12). A variable frequency oscillator (10) produces a variable frequency output in proportion to the pressure applied to the transducer (12). A local oscillator (16) produces a fixed frequency signal which is mixed with the variable frequency signal in a mixer-demodulator (14) to produce an audio depth signal. The audio depth signal is provided to up/down counters (30). A time base and synchronizer circuit (24) sequences the counters (30) for an up frequency count and a down frequency count of the audio depth signal. When the difference count exceeds a preset limit, a maximum rate of depth change circuit (34) produces an alarm signal which is transmitted through a beep timer circuit (36) to activate an audio driver and output circuit (28) which produces alarm signal at an audio disk (38). This gives a warning of too rapid of an ascent or descent by the diver.

Abstract: A dual-tone multiple frequency signal generator is provided for use with telecommunications systems, data transfer systems and other applications. The tone encoding system utilizes MOS/LSI integrated circuitry on a single chip powered directly by telephone line voltages. An electronic keyboard circuit provides synchronized pulses to decode single-pole, single-throw keyboard switches by row and column. A crystal-controlled oscillator generates a reference frequency which is divided according to the row and column of an activated keyboard switch to obtain two pulse signals having frequencies representative of the activated switch. The outputs of the divider circuitry are fed to a programmed logic array which generates two digitally coded signals each representing a sinusoidal waveform. A digital-to-analog ladder network converts the digitally coded signals to continuous sine waves, and an operational amplifier combines the sinusoidal waveforms to provide a dual-tone output.