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Quiz Competition Buzzer For Eight Players/Teams

We designed a Quiz Buzzer circuit that can be used for eight players/teams in quiz competitions organized by schools or colleges.

Normally, quiz circuits are designed with microcontrollers, but this simple circuit does not use any microcontroller. The heart of this circuit is a priority encoder, 74LS373. The author’s prototype built on a breadboard is shown in Fig. 1.

DIY Quiz Buzzer Circuit
Fig. 1: DIY Quiz Buzzer Circuit on Breadboard

Components Required

Parts List
Semiconductors:
IC1-LM7805, 5V voltage regulator
IC2-74LS373 priority encoder
T1, T2-2N2219 NPN transistors
BR1-1A bridge rectifier
LED1-LED9-5mm LEDs
Resistors (all 1/4-watt, ±5% carbon):
R1-1-kilo-ohm
R2-R10-5.6-kilo-ohm
R11-R18-100-ohm
Capacitors:
C1– 1000μF, 35V electrolytic
Miscellaneous:
CON1– 2-pin connector
S1-S8– Push-to-on switches
X1– 230V AC primary to 9V, G39 500mA secondary transformer

Quiz Buzzer Circuit

Fig. 2 shows the circuit diagram for the quiz competition buzzer.

It is built around a step-down transformer (X1), a bridge rectifier (BR1), a 5V voltage regulator LM7805 (IC1), eight push-to-on switches (S1 through S8), priority encoder IC 74LS373 (IC2), two NPN transistors 2N2219 (T1, T2), a piezo buzzer (PZ1), nine LEDs (LED1 through LED9), and a few other components.



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