Contest buzzer systems are widely used in school, colleges and TV programs. The team that presses the doorbell earlier has the right to give the answer. Sometimes it becomes very difficult to identify which computer has pressed the button when two computers press the buzzer within a very small time gap. In such cases, the decision may be biased due to human intervention. The buzzer of the contest presented here addresses the problem mentioned above. This test buzzer disables the other inputs as soon as the first buzzer is pressed. This test buzzer can be used for up to eight computers. It builds around 8051 microcontroller (AT89C51).
This contest buzzer system has eight input pins for eight computers. The output is displayed on a seven-segment display (microcontroller interface), which shows the number corresponding to the equipment that has pressed the first button. A buzzer is also emitted for a short duration to give an acoustic alarm. The connections of the seven segments, the input pins and the output pins are shown in the circuit diagram.
For details, see "seven interface segments". There are a total of nine input pins. Eight pins of the P2 port of the microcontroller correspond to eight inputs and one stop pin to reset the buzzer system. On the output side a segment seven is connected to display the corresponding output number. There is also an arrangement to sound a buzzer for a small duration.
When the system starts, segment seven shows no output. The microcontroller continues to scan the input pins. As soon as any of the inputs are pressed, the buzzer sounds for a short duration. Segment seven shows the number corresponding to the input being pressed. Now even if you press any other input pin, there will be no effect on the system until the stop button is pressed to restart the system.