Quizmaster Board is designed to be used in quiz shows. Quizmaster determines who is first to press an answer button, is a problem since more than one person may appear to have pressed the button at same instant of time. To differentiate between the minute time differences in between two persons pressing the buttons is almost impossible for human being.

Only electronic device can do it with accuracy and therefore our Quizmaster is very popular now days with growing competitions being arranged. The circuit given here helps to make students familiar with an interesting device and helps develop understanding and interest of electronics bedsides commercial utilization.
About the circuit :
As shown in the diagram, the circuit is designed around ICs 4012 (NAND GATES) and 4013 (D Flip flop).
The IC 4012 which has two dual FF with SET and CLEAR inputs; is used to  set/ reset FFs. When the competitor presses a button/push switch (say S1), the FF1 gets SET (Q = 1, Pin13) irrespective of D and clock inputs. However to avoid action by noise pulses, the D input and Clock input is connected to logic HI.

This action forces Q output to go HI and Q- (pin12) to go LO. Hi at Q output will force LED D1 to glow through driver transistor T1. The Q- output is connected to inputs of all NAND gates
(N2, N3, N4) in the remaining FF circuits. The NAND gate outputs are in turn connected to CLEAR input of FF ( FF2, FF3, and FF4). This will produce LO state at all other FF outputs (Q) by virtue of being cleared.
The circuit is reset after a round is finished before the next round is to be started. The reset switch S5 shown here forces one input of all.
When next time another button is pressed, the corresponding FF gets SET and all other FFs gets reset thus glowing another corresponding LED.
Thus with press of a push switch, corresponding LED glows and all others get inhibited. The circuit also has a common buzzer, which gives audio alarm when any of the LED glows so as to attract attention of viewers and judges. The common buzzer is activated by another set of transistors driven from same output of FFs. All the buzzer signals are ORed through D5 – D8. The circuit can be easily extended to more number of competitors. For each additional competitor/participant an extra FF and a NAND gates is required to be connected. These NAND gates can be Red and the same result can be obtained. To avoid possibility of interference on account of long length of wires ,the low impedance of RC network connected to SET input has to be kept low .If such problem is faced ,value of R1 –R8 can be reduced to 1k.

Quizmaster Board is designed to be used in quiz shows. Quizmaster determines who is first to press an answer button, is a problem since more than one person may appear to have pressed the button at same instant of time. To differentiate between the minute time differences in between two persons pressing the buttons is almost impossible for human being.

Only electronic device can do it with accuracy and therefore our Quizmaster is very popular now days with growing competitions being arranged. The circuit given here helps to make students familiar with an interesting device and helps develop understanding and interest of electronics bedsides commercial utilization.
About the circuit :
As shown in the diagram, the circuit is designed around ICs 4012 (NAND GATES) and 4013 (D Flip flop).
The IC 4012 which has two dual FF with SET and CLEAR inputs; is used to  set/ reset FFs. When the competitor presses a button/push switch (say S1), the FF1 gets SET (Q = 1, Pin13) irrespective of D and clock inputs. However to avoid action by noise pulses, the D input and Clock input is connected to logic HI.

This action forces Q output to go HI and Q- (pin12) to go LO. Hi at Q output will force LED D1 to glow through driver transistor T1. The Q- output is connected to inputs of all NAND gates
(N2, N3, N4) in the remaining FF circuits. The NAND gate outputs are in turn connected to CLEAR input of FF ( FF2, FF3, and FF4). This will produce LO state at all other FF outputs (Q) by virtue of being cleared.
The circuit is reset after a round is finished before the next round is to be started. The reset switch S5 shown here forces one input of all.
When next time another button is pressed, the corresponding FF gets SET and all other FFs gets reset thus glowing another corresponding LED.
Thus with press of a push switch, corresponding LED glows and all others get inhibited. The circuit also has a common buzzer, which gives audio alarm when any of the LED glows so as to attract attention of viewers and judges. The common buzzer is activated by another set of transistors driven from same output of FFs. All the buzzer signals are ORed through D5 – D8. The circuit can be easily extended to more number of competitors. For each additional competitor/participant an extra FF and a NAND gates is required to be connected. These NAND gates can be Red and the same result can be obtained. To avoid possibility of interference on account of long length of wires ,the low impedance of RC network connected to SET input has to be kept low .If such problem is faced ,value of R1 –R8 can be reduced to 1k.