Abstract: An electrical control system includes a matrix made up of electrically conductive lines and columns which cross each other at predetermined locations where a plurality of connecting circuits are provided for respectively electrically connecting the lines and columns to each other at selected locations. The connecting circuits respectively include Zener diodes respectively having threshold voltages distributed among a plurality of different threshold voltages of different discrete magnitudes. The level of the signals supplied to the lines can be correspondingly modulated. A receiving structure electrically connected to the columns for receiving output signals therefrom includes components having thresholds of detection corresponding to the magnitudes of the threshold voltages of the Zener diodes of the connecting circuits. These components of the receiving structure include operational amplifiers polarized by Zener diodes which are connected in cascade.