Circuit for operating a bar graph display panel

Abstract

A bar graph display panel comprises a gas-filled envelope containing a series of fine, closely-spaced cathode lines connected in groups so that they can be energized sequentially and individually. The panel also includes an anode film supported on the face plate and aligned with and in operative relation with the series of cathode lines. The anode and cathodes are closely spaced and the panel contains an ionizable gas at relatively high pressure. In order to use the display panel to display a bar of light, the anode and cathodes are connected in an operating circuit wherein each of the cathodes is energized or scanned and caused to glow sequentially. An analog signal to be displayed as a bar of light and a ramp signal are coupled to a comparator, the output of which energizes the anode electrode. When the two input signals are equal, the output of the comparator is zero, the anode is cut off, and the time in the scanning cycle when this occurs determines the number of cathodes which have been energized and the length of the bar of light displayed thereby. The scanning operation is carried out continually at such a rate that the bar of light appears to be stationary but is changeable in accordance with changes in the input analog signal.

What is claimed is: 
     
       1. A bar graph display system comprising a display panel comprising a gas-filled envelope including a base plate and a viewing face plate hermetically sealed together,   a plurality of thin, parallel, linear cathodes disposed in a series along the surface of said base plate and positioned sufficiently close together so that, as the series of cathodes is energized and selected cathodes are caused to exhibit cathode glow, the glow of adjacent cathodes appears to blend to form a bar of light, said series of cathodes including a first cathode, a last cathode, and intermediate cathodes,   a reset cathode positioned adjacent to and ahead of the first cathode in said series for use in starting a scanning cycle for said series of cathodes,   an anode electrode disposed on said face plate overlying said series of cathodes,   conductors connected to said cathodes and connecting said cathodes in groups with a single common conductor connected to each such group,   a separate cathode driver connected to each common conductor for energizing each cathode in turn along said series of cathodes,   a reset cathode driver connected to said reset cathode and adapted to be energized first before said separate cathode drivers in a cathode scanning cycle,   an anode driver connected to said anode electrode for applying operating potential thereto, and   a circuit coupled to said anode driver including a signal comparator circuit having a single output connected to said anode driver, said comparator circuit having two inputs, one input comprising a source of a sawtooth voltage, and the second input comprising a source of an analog signal to be represented in said panel by a bar of light made up of a group of energized cathodes, said cathode drivers continually energizing said cathodes in said series and causing said cathodes to exhibit cathode glow as long as there is an output from said comparator and said anode driver is energized thereby and energizes said anode. .Iadd. 2. An indicator device comprising   an envelope containing an ionizable gas at a pressure capable of maintaining a cathode glow discharge,   at least one series of n cathodes spaced from one another along an insulating surface within said envelope, where n is an integer greater than 3,   an anode in gas discharge relationship with each cathode of the series,   first circuit means for respectively scanning said series of cathodes, each such scan beginning with the first cathode in the series and proceeding along the cathodes in the series one after another,   second circuit means controlling the voltage applied to the anode while the cathodes are being scanned,   said second circuit means including a counter for counting as successive cathodes are scanned and maintaining a count which corresponds to the cathode being scanned as the scan moves from cathode to cathode,   a ramp generator for producing a saw-tooth or ramp-shaped waveform during each scan of the cathodes in response to a succession of applied input pulses, the value of the saw-tooth voltage increasing as the counter counts,   a comparison circuit having two input terminals, one connected to said ramp generator and the other for receiving an input signal having a value to be displayed on said cathode series,   said comparison circuit applying a signal to said anode when said ramp voltage bears a predetermined relationship to said input signal, and   means connected to the output of said counter and responsive to the full count thereof for applying a reset signal to portions of said second circuit means in advance of the initiation of a cycle of operation of said     
     
     
        first and second circuit means. .Iaddend..Iadd. 3.  An indicator device as in claim 2 wherein said counter has a total count of n and it recycles for each new scan of the cathodes. .Iaddend. .Iadd. 4. An indicator device as in claim 2 wherein   said cathodes are interconnected into n circuits, where n is 3 or more, each said circuit including a different group of every nth cathode, and wherein   said first circuit means includes a drive circuit for energizing said n circuits in sequence and successively repeating said sequence,   further including input circuit means connected to said drive circuit and said counter. .Iaddend..Iadd. 5. An indicator device as in claim 2 and including an anode driver coupled between said comparison circuit and said anode. .Iaddend.