8 Users 74LS232 Quiz Timer

The quiz buzzer circuit given here can be used for up to eight players.

The circuit uses IC 74LS373 along with few components that are readily available in the market. The circuit has power supply section, buzzer, LED, reset-switch, and Team Switch.

IC 74LS373 is an octal latch, used to transfer the logic state at data input pins D0 through D7 to the corresponding Q0 through Q7 outputs. Data pins D0 through D7 are normally pulled low by resistor pack RN1, One terminal of momentary push-to-on switches BT1 through BT8 is connected to +5V, while the other terminal is connected to the respective data input pins. Capacitor C6, C7, C8 (filter) and C9 (de bounce) prevent malfunction like multiple output switching on due to oscillations. Switch connected to RSTA, RSTB used for reset the circuit. The BT1 through BT8 switches are to be extended to the players through cord wire. LED T1 through T8 represent Player 1 through Player 8 , all the switches BT1 through BT8 are open and Q0 through Q7 outputs of IC 74LS373 are low. As a result, LED T1 through T8 is off. When a player momentarily presses his respective switch, the corresponding output data pin goes high and respective LED glows. At the same time, the buzzer SG1 sounds as transistor Q2 conducts. Simultaneously, the base of transistor Q1 becomes high, this pulls Latch-enable (LE) pin 11 of IC2 to ground latching all the Q0 through Q7 outputs which restricts further change in the output state due to any change in the state of switches S1 through S8 by any other player. Only one of the eight LED glows until the circuit is reset by Reset-Switch connected across RTSA RSTB.

Power supply Circuit comprises of Bridge rectifier B1, Capacitors C1 through C5, 5V Regulator IC1 (LM7805), LED1 is power indicator, On/Off switch is connected across SW1 and SW2, B+ B- is used for connecting Battery backup, on event of mains power failure circuit will work with power from 9v Battery.