DIY Quiz Buzzer Circuit for School/College

The DIY Quiz Buzzer Circuit operates entirely through analog and discrete digital logic, without requiring any programmable microcontrollers. Power originates from a 230V AC mains supply stepped down via transformer X1, rectified by the 1A bridge rectifier BR1, smoothed by the 1000uF 35V electrolytic capacitor C1, and regulated down to a stable 5V DC rail by the LM7805 voltage regulator (IC1). This regulated supply powers the logic and indicator stages. When a participant presses one of the push-to-on switches (S1 through S8), it inputs a signal into the 74LS373 priority encoder (IC2). The priority encoder instantly locks out subsequent inputs and identifies the first switch pressed, ensuring fair play. The output from the encoder drives the corresponding 5mm LEDs (LED1 through LED9) to visually indicate which player buzzed in first. Simultaneously, switching transistors T1 and T2 (2N2219 NPN transistors) act as electronic switches to drive the piezo buzzer (PZ1), providing an audible alert when any valid button press occurs. Resistors R2 through R10 (5.6k) act as pull-down or current-limiting networks alongside R1 (1k) and the 100-ohm current-limiting resistors (R11 through R18) configured across the LED and transistor interfaces to ensure proper logic level stability and component protection.