When there was no microcontroller and integrated circuits at that time Keypad matrix was controlled by diodes and momentary push on switch. Due to out of space, we have shown 3 Bit keypad matrix by 8 numbers 0 to 7 Three SET RESET Flip-flop circuit used for Bit 1, Bit 2 and Bit 3 position. When we press 5 (1 0 1) both Bit 3 and Bit 1SET Relay and Bit 2 RESET Relay get positive current to energized. This way the Keypad is working.
