Abstract: An optoisolator includes one or more light-emitting diodes (LEDs) within a compartment defined by walls of photocells, where the majority of light emitted by the LED impinges directly upon a photocell and is converted to electricity with a minimum of loss. The photocells are attached together by abutting the end of one photocell to the surface of another, as in a butt joint. In one embodiment, the LEDs is inserted into an opening in the compartment and secured by filling the compartment with a light-transmissive, non-conductive material. In another embodiment, the LEDs and photocells are mounted to a substrate. Optionally, each photocell has more than one electrically-independent photosensitive surface.

Abstract: An isolation amplifier that transmits data to a receiver via a current loop, where the isolated portion of the circuit is powered by a photovoltaic array illuminated by a light source powered directly by the current loop. Optionally, the photovoltaic array is additionally illuminated by any excess power tapped from the current loop by the non-isolated portion of the circuit. Preferably, the light source is an array of light-emitting diodes. Preferably the photovoltaic array is an array of photocells sensitive to the same wavelengths emitted by the light-emitting diodes. Preferably, there are optical conductors connecting the LED's to the photocells.

Abstract: A touch sensitive device is associated with at least one key of an electronic musical instrument such as an electronic organ, includes a layer of a pressure responsive, variable conductance material, and exhibits a switching action when subjected to pressure beyond a threshold pressure, any increase in pressure thereafter providing an increase in conductance up to a saturation pressure. The device may be used either as a combined switch and amplitude control or may be used in associated with one or more capacitors to provide either a high pass or low pass touch-control audio filter. In a totally polyphonic instrument a tone generator and touch-control filter are respectively associated with and responsive to each key depression, the output signal from each activated filter being coupled preferably to audio mixer circuitry.

Abstract: A low noise resonant filter of wide dynamic range and low distortion is formed from a number of series-connected filter stages, each comprising a current integrating amplifier driven from transconductance formed from a bipolar differential pair with feedback to one member of the transconductance pair to maintain its transconductance substantially constant. A further bipolar differential pair transconductance at the input stage operates with a widely variable transconductance and provides soft limiting and wide dynamic range, especially when the filter is operated in the resonant mode.

Abstract: The keyboard type instrument includes circuitry for controlling an envelope generator and a voltage controlled oscillator which in sequence operates a voltage controlled filter, and a voltage controlled amplifier both of which receive control signals from the envelope generator. The keys of the keyboard preferably have a common variable conductance touch sensor or transducer associated therewith which is responsive to key depression pressure in excess of a predetermined threshold pressure to control one or more audible characteristics of the played note. In one embodiment vibrato, pitchbend, brilliance and volume of the note are controllable. Associated with the keyboard is selection means including a plurality of audible characteristic selectors and variable means delimiting the range of the audible characteristics.