Abstract: The keypad interface element of this invention uses a relaxation oscillator and a digital keypad processor having a counter/timer to decode specific keys. The RC portion of the relaxation oscillator includes a resistance ladder and a set of momentary on pushbutton switches disposed change resistance dependent upon which key is pressed. This causes the relaxation oscillator to produce an output signal having a corresponding frequency. The counter/timer of the digital keypad processor produces a count corresponding to the oscillator frequency. The digital keypad processor latches and holds a binary number specifically identifying the depressed key. A state machine in the digital keypad processor provides transient-free, noise immune keypad decoding.

Abstract: The keypad interface element of this invention uses a relaxation oscillator and a digital keypad processor having a counter/timer to decode specific keys. The RC portion of the relaxation oscillator includes a resistance ladder and a set of momentary on pushbutton switches disposed change resistance dependent upon which key is pressed. This causes the relaxation oscillator to produce an output signal having a corresponding frequency. The counter/timer of the digital keypad processor produces a count corresponding to the oscillator frequency. The digital keypad processor latches and holds a binary number specifically identifying the depressed key. A state machine in the digital keypad processor provides transient-free, noise immune keypad decoding.

Abstract: Disclosed are methods and apparatus for isolating and driving a power supply or power amplifier circuit. The circuits and methods provide for using a modulated PWM input signal and its complement to drive one or more core-less transformers providing an isolated power supply circuit output signal reproducing the PWM input signal. Preferred methods of the invention are disclosed in which steps for receiving and modulating a PWM input signal and its complement are included. In further steps, the modulated PWM signal and its complement control an isolated output driver to provide a power supply circuit output signal reproducing the PWM input signal. Embodiments of the invention are disclosed in which a circuit is configured for receiving a PWM input signal, providing isolation, and outputting a PWM output signal. The circuits include modulators for modulating a PWM input signal and its complement.

Abstract: An apparatus for monitoring speaker cone displacement in an audio speaker includes: (a) an electromagnetic coil structure; (b) a ferrous core structure; the ferrous core structure and the electromagnetic coil structure being mounted with the speaker to effect variable electromagnetic coupling between the ferrous core structure and the electromagnetic coil structure as the speaker cone moves; (c) a signal injecting circuit coupled with the electromagnetic coil structure for injecting a predetermined input signal into the electromagnetic coil structure; and (d) a signal monitoring circuit coupled with the electromagnetic coil structure; the signal monitoring circuit receiving an output signal from the electromagnetic coil structure and generating an indicating signal based upon the output signal; at least one signal characteristic of the indicating signal being related with the cone displacement.