Abstract:
A potentiometer device including a resistor path and a conductive film spaced therefrom. The film may be brought in contact with the resistor by exerting finger pressure. The tap voltage is stored in a memory and displayed by means of LEDs.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a potentiometer device. Electrical potentiometers have been known for many decades. They comprise a resistor path made of wire or carbon in circular or elongated shape and a tape member or slider movable along the resistor path and making contact therewith. Usually, the tap is manually moved and its position may be recognized. 
     Manual adjustment of a potentiometer takes some time, in particular if a predetermined tap position is to be made. Sometimes this delay is embarrassing. For example, in electronic musical instruments, the so-called &#34;registration&#34; is selected by means of potentiometers and has to be readjusted during play. The handling may be facilitated by replacing the potentiometers by sets of switches, but these, of course, have only a limited number of settings. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a potentiometer device which can be rapidly set to any of its potential settings. 
     It is a further object of the present invention to provide such a potentiometer device with means permitting display of the selected setting. 
     In accordance with the present invention, the potentiometer device comprises a resistor path which preferably is of the strip-shaped, elongated form. an electrically conductive film member is mounted spaced above the resistor path and may be brought in contact therewith by finger pressure, the conductive film member forming the tap terminal of the potentiometer. The tap voltage is thus supplied only during the contact or finger pressure interval, and the setting so selected is to be memorized. The most simple memory, for example, would be a sample-and-hold circuit, but it is preferred to connect the film member to the input of an analog-to-digital converter and to load the output of the latter into a RAM (random access memory) which then holds a digital value representative of the tap voltage. The number of digits of such value determines how fine the setting can be made. Light emitting diodes may be used to display the respective setting. In order to avoid floating of the A/D converter input upon release of the film member, it is preferred to have the film member connected, via a resistor, to a reference potential and to check by means of a comparator whether the actual voltage at the tap differs from said reference potential, and to start a conversion cycle upon only a predetermined difference. 
     The optical display is useful not only in conjunction with manual setting. Many modern electronic organs permit memorizing a registration once elaborated and reading the memorized settings into the internal memory of the organ; light emitting diode displays may be easily controlled by such externally produced signals so that the player has full control of all his registers. 
     Preferred embodiments of the invention are illustrated in the attached drawings and will be explained hereunder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows schematically and not to scale the input and display portion of the potentiometer device in section. 
     FIG. 2 is a partial plan view of the device of FIG. 1. 
     FIG. 3 is a block circuit diagram of the potentiometer device according to the invention including a plurality of input and display portions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first of FIG. 1 and FIG. 2, a support or substrate 10 carries an elongated resistor path 12 and, lateral with respect thereto, a series of light emitting diodes LED 14. A spacer film 16 is apertured for the LED and for the resistor path and insures that a film member 18 contacts resistor path 12 only upon pressure exertion upon film member 18 by exertion of pressure on flexible cover 20. The latter has an electrically conductive layer on its side facing the resistor path. The terminals of the LEDs extend through support 10 to the rear side thereof. The described layout may, of course, be modified; for example, the LEDs may be mounted centrally with respect to two parallel resistor strips, etc. 
     Referring now to FIG. 3, the device comprises sixteen register potentiometers of an electronic organ and allocated processing circuitry. Of the sixteen resistor/film/LED units, only two, however, are depicted in FIG. 3. The taps are scanned in time multiplex. For this purpose, the sixteen taps are connected to the analog inputs of analog multiplexer 30 while the terminals of the sixteen resistors are respectively connected to ground potential and to a supply voltage of, say, 5 volts. Upon finger pressure on the film member, accordingly, a voltage between 0 and 5 volts is fed to the respective multiplexer input. The scanning is effected by means of clock generator 32 followed by a 4-bit counter 34. 
     The output of multiplexer 30 is applied to a load resistor of, say, 50 ohms and to the input of a comparator 36 whose other input is connected to ground. As long as a film member does not make contact with its resistor path, both the comparator inputs are at ground potential so that the comparator output does not produce a control signal. 
     Upon recognition of a potential difference at its inputs, comparator 36 produces a START signal for analog-to-digital converter 38 which converts the analog output signal of multiplexer 30 into an 8-bit digital signal. The respective address is given by counter 34, and under control of a load command on line 40, output data of the converter are written into random access memory 42. The address given by counter 34 as well as data read from memory 42 are used for the internal control of the musical instrument. Further, they are used for display control. 
     A decoder 44 fed with addresses from counter 34 provides a 4-into-16 conversion and supplies a column driver circuit 46 while data from RAM 42 supply a line driver circuit 48. The outputs of driver circuits 46, 48 form a matrix in the intersections of which the LEDs are connected. In result, the LED series of each resistor/display unit indicates the point next to the site where the player touched in the film member. 
     It will be understood that the units disposed side by side may all share a common substrate, a common spacer film, and a common transparent cover film because such a design reduces production costs. Also, the player may set all units by one single finger stroke across all sixteen units. 
     It will be further understood that the display may be set also if the data are not read from RAM 42 but are supplied by an exterior source.