• Tags: logic-gates, Boolean, truth-table
• Difficulty: Foundation

Digital electronics uses binary logic: HIGH (1, typically 5V) and LOW (0, typically 0V). OR gate: Y = A + B. Output is 1 if ANY input is 1. Truth table: (0,0)->0, (0,1)->1, (1,0)->1, (1,1)->1. Implemented using diodes: two diodes with anodes connected to inputs, cathodes to output through a resistor. AND gate: Y = A.B. Output is 1 only if ALL inputs are 1. Truth table: (0,0)->0, (0,1)->0, (1,0)->0, (1,1)->1. NOT gate (inverter): Y = A'. Output is complement of input. (0)->1, (1)->0. Implemented using a transistor in common-emitter configuration: input HIGH saturates transistor (output LOW), input LOW cuts off transistor (output HIGH). Boolean algebra rules: A+0=A, A+1=1, A.0=0, A.1=A, A+A=A, A.A=A, A+A'=1, A.A'=0.