Abstract: A telephone answering device (TAD) includes a remote access mode which is operative responsive to dual tone multi-frequency (DTMF) signals. At least three bandpass filters each receive an input signal from a telephone line interface provided in the TAD. A software controlled sampling section receives outputs from all the bandpass filters for sampling outputs from the bandpass filters, the sampling section including a multiplexer which receives the outputs from all of the bandpass filters, and a peak hold circuit coupled to an output of the multiplexer. An analog-to-digital converter receives an output from the peak hold circuit, and a digital controller receives the output of the analog-to-digital converter for controlling operations of the TAD in a remote access mode responsive to the detected DTMF signals. First and second ones of the bandpass filters have respective center frequencies corresponding to frequencies of respective DTMF signals and a third bandpass filter has a different center frequency.

Abstract: A speakerphone which employs non-linear amplifiers to compress transmit and receive signals, and level detectors to determine levels of the compressed transmit and receive signals. Compressed transmit and receive signal levels are compared against one another by a comparator with hysteresis, to enable one of two speakerphone modes of operation--either a transmit mode or a receive mode. Fixed attenuators are switched into either the receive signal path or into the transmit signal path, depending upon the current speakerphone mode. The speakerphone functions described herein are readily implemented using inexpensive control circuitry and a standard telephone line interface, which can be shared by a telephone handset and other components of an integrated telephone system.

Abstract: A system for locating an object. The system includes an electronic device, a wireless transmitter for outputting a transmitted signal, and a receiver wherein one of the receiver or the transmitter is mounted within the electronic device and the other is positioned remote therefrom. The receiver comprises a wake up timer circuit for periodically generating a wake up signal, a wireless signal receiver being activated by the receipt of the wake up signal from the wake up timer circuit for generating a detect signal when the wireless signal receiver circuit receives the transmitted signal from the transmitter; and an audible signal generator circuit for generating an audible signal upon receipt of the detect signal from the wireless signal receiver circuit. The wake up timer circuit and the wireless signal receiver circuit are disabled when the audible signal generator circuit generates the audible signal.

Abstract: A digital automatic gain control system includes an envelope detector coupled to a system input for converting an AC input signal into a DC output signal. An analog-to-digital converter has an input coupled to receive the output signal of the envelope detector and an output coupled to a digital register controlled by a digital control circuit. A programmable gain amplifier has control inputs coupled to receive an output of the digital register for controlling the gain of the programmable gain amplifier such that the signal level at a system output of the programmable gain amplifier remains substantially constant as the signal level at the system input varies within a specified dynamic range.

Abstract: A system for locating an object, particularly a remote control, has a transmitter and a receiver, wherein the receiver has circuitry implementing power saving features. The receiver includes circuitry for turning off portions of the circuitry not essential for performing the current task. The receiver additionally only activates the wireless signal receiver portion of the circuitry periodically for short periods of time. The time of activation represents a small fraction of the operational time if the wireless signal receiver portion were to remain activated continuously.