1. CIRCUIT
IDEAS
SCHOOL/COLLEGE S.C. DW
IVEDI
QUIZ BUZZER
GOVINDA RAJU TEKUMUDI petition. The circuit uses IC 74LS373 section is IC 74LS373, an octal
and a few passive components that are latch that is used to transfer
M
anual buzzers used for quiz readily available in the market. the logic state at data input pins
competitions in schools and The circuit can be divided into two D0 through D7 to the corresponding
colleges create a lot of confu- sections: power supply and quiz Q0 through Q7 outputs. Data pins D0
sion in identifying the first respondent. buzzer. through D7 are normally pulled low
Although there are circuits using PCs Fig. 1 shows the power supply sec- by resistors R1 through R8, respec-
and discrete ICs, they are either too tion. The regulated 5V power supply tively.
expensive or limited to only a few for the quiz buzzer section is derived One terminal of push-to-on
number of players. from AC mains. The 230V AC mains switches S1 through S8 is connected
The quiz buzzer circuit given here is stepped down to 7.5V AC by trans- to +5V, while the other terminal is
can be used for up to eight players, former X1, rectified by bridge rectifier connected to the respective data input
which is maximum in any quiz com- BR1, filtered by C1 and regulated pins. The switches are to be extended
by regulator to the players through cord wire. The
IC1. Capacitor torch bulbs BL1 through BL8 can be
C2 bypasses housed in boxes with the front side of
ripples in the the boxes covered with a white paper
regulator out- having the name or number of the
put. contestant written over it for easy
Fig. 2 identification. Place the boxes above
shows the the head level so that these can be
quiz buzzer seen by the audience also.
section. At the When the power is switched on us-
Fig. 1: Power supply heart of this ing switch S9 (provided terminals ‘A’
Fig. 2: Circuit of school/college quiz buzzer
WWW.EFYMAG.COM ELECTRONICS FOR YOU • MAY 2006 • 87
CMYK

2. CIRCUIT
IDEAS
and ‘B’ of both the power supply and tarily presses his respective switch, the is tied to ground to latch all the Q0
quiz buzzer sections are intercon- corresponding output data pin goes through Q7 outputs. This restricts fur-
nected), the circuit is ready to use. high. This triggers the corresponding ther change in the output state due to
Now all the switches (S1 through S8) SCR and the respective bulb glows. At any change in the state of switches S1
are open and Q0 through Q7 outputs the same time, the piezobuzzer (PZ1) through S8 by any other contestant.
of IC 74LS373 are low. As a result, the sounds as transistor T1 conducts. Only one of the eight torch bulbs
gates of silicon-controlled rectifiers Simultaneously, the base of tran- glows until the circuit is reset by on/
SCR1 through SCR8 are also low. sistor T2 becomes high to make it con- off switch S9. Note. The complete kit
As soon as a contestant momen- duct. Latch-enable (LE) pin 11 of IC2 is available at Kits ‘n’ Spares outlet.
88 • MAY 2006 • ELECTRONICS FOR YOU WWW.EFYMAG.COM
CMYK