An array of relays using the contact to the negative rail to control the rows and/or columns to turn off. With this setup it is not possible to turn off less than one entire row/column but it is possible to keep one only LED on. Each LED's state is the opposite of the relays, equivalent to a "NOT" gate. The dual diodes at be bottom left of each relay is playing the role of an "OR" gate. Therefore, each assembly of LED+relay+diodes is a "NOR" gate. LED is on in each position for which neither the row nor the column is switched.
