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PC Based Quiz Buzzer: Project tutorial using parallel port

By Harsha and Veena


          Here is a PC based Game show/ quiz buzzer, which makes a quiz 'priority less'. Instead of allowing only the first person who presses the buzzer first to answer, this buzzer introduces a new idea called 'Priority passing'. Uses PC parallel port to input response from the buzzer.  


         The attraction of any game show depends on the visual effects. The way in which they present different rounds makes the game shows effective. The good Quiz show always contains one or more buzzer rounds.
The buzzer makes a round of a Quiz show 'fastest finger first '. The active buzzer makes the team to first respond to the question. A common question will be asked for all the teams in these rounds. The team which presses the buzzer first gets first chance to answer. To avoid confusion of the teams to be answered when one or more team presses the buzzer almost simultaneously, buzzer circuits are used.

         Instead of just showing who pressed the buzzer using some LED or electric bulb, if has some visual effects, audio effects and different options that makes the show entice. So our approach is to make this possible which includes all the features. This project makes the show attractive and easy to operate. This Quiz buzzer is built with the view of making the game show priority less.

        This project uses PC parallel port to input user's response from the switches placed in the participant's table. Response of the teams can be projected on to a screen. Number of all the teams will be displayed in the screen in order of the response.

        This project uses Turbo C version 3.0 for programming. If you don't know the parallel port interfacing, read http://electrosofts.com/parallel : Parallel port interfacing tutorial. If you are using windows xp and other compilers, you may need to read Parallel port interfacing: windows. You can use this idea and convert the project for windows, try it...


This project uses parallel port in normal( unidirectional ) mode. So, we have only 5 input pins available. Here, we assumed there are 6 teams. So we need extra input pins. This can be done by multiplexing the signals.

Circuit of the quiz buzzer consists of the following components:

  • Multiplexer IC 74157

  • 10kΩ resistors (6)

  • 5volt dc power supply

  • D-25 type connectors

  • Push switches (6)

        The circuit diagram is as shown above.  the pins 10,11,12,14 of the D-25 connector are connected to the IC as in the diagram. The pins from 18 to 25 are grounded. Another end of the cable is connected to the LPT1 port of the PC.


Logic diagram of IC 74157

Next part contains the C code of the project and description of the working.

Continue to next part...



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