Electrolytic display cell and control therefor

An electrolytic display comprising:

• a display electrolytic cell including a counter electrode, a reference electrode and a plurality of display electrodes spaced from each other and from said counter electrode, and an electrolyte contacting all said electrodes and filling the space therebetween, said reference and display electrodes being in contact with one face of said electrolyte and said counter electrode in contact with the opposite face;
• a negative voltage source;
• a constant current generator so connected between said counter electrode and said reference electrode as to cause a positive voltage to appear on said reference electrode;
• an operational amplifier having its noninverting input connected to said reference electrode;
• and
• switching means connected to each of said display electrodes for selective connection of each to said negative voltage source or to the output of said amplifier;
• whereby the magnitude of erasing voltage supplied to said display electrodes when connected by said switching means to the output of said amplifier is dependent upon the impedance of said cell as determined by said reference electrode and constant current generator.