8 Channel Quiz Buzzer Circuit using Microcontroller

Quiz buzzers are used often at places like educational institutions where it is required for game shows. Conventional systems require human intervention to decide which team has pressed the button and this system can be erroneous and even biased. Another problem arises when two members pressed the button at a negligible interval and it is difficult to guess who has pressed the buzzer first. Here we designed an automatic quiz buzzer system such that when more than one team presses the buzzer, the delay is accurately taken into account and number is displayed. We build the circuit using a microcontroller which scans the input from push buttons and displays the corresponding number on a display device.  It is a simple circuit with minimum number of components and sans any complexities. The microcontroller takes into account the time delay between two buttons and the accurate number is displayed.  Even though this system is only for 8 teams, more teams can be added by using another set of 8 push buttons.

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Principle Behind the Quiz Buzzer Circuit:

The circuit is a simple embedded system with a set of 8 push buttons being the input devices, a microcontroller as the controller and the output devices being a buzzer and a display. The whole operation is carried out by a microcontroller through a program written in C language and dumped inside the microcontroller. When one of the buttons is pressed, the buzzer starts ringing and the corresponding number is displayed on the 7 segment display.

Circuit Diagram of 8 Player Quiz Buzzer using Microcontroller:

8 Player Quiz Buzzer Circuit using Microcontroller – ElectronicsHub.Org

Quiz Buzzer Circuit Design:

The whole design process involves six steps. First step requires designing the circuit; the second step is drawing the circuit on any software like Proteus. The third step involves writing the code using high level language or assembly language and then compiling it on a software platform like Kiel uVision. The fourth step is dumping the code in microcontroller and fifth step is simulating the circuit.

The circuit involves using five major components – a Microcontroller, 8 SPST push buttons, a buzzer and a common cathode 7 segment display.  The microcontroller used in this case is AT89C51, an 8 bit microcontroller manufactured by Atmel.

Reset Circuit Design: The reset resistor is selected such that the voltage at the reset pin, across this resistor is at minimum of 1.2V and the width of the pulse applied to this pin is greater than 100 ms.  Here we select a resistor of 100K ohms and a capacitor of 10uF.

Oscillator Circuit Design: The oscillator circuit is designed using a crystal oscillator of 12 Mhz and two ceramic capacitors each 15pF. The crystal is connected between pins 18 and 19 of the microcontroller

Microcontroller Interfacing Design: The set of 8 push buttons are interfaced to port P1 of the microcontroller and a buzzer is interfaced to the port pin P0.0. The 7 segment display is interfaced to the microcontroller such that all the input pins are connected to port P2.

Microcontroller Code: The code can be written using C language or assembly language. Here we select to write the program in C language using Kiel uVision. This is accomplished by the following steps

1. Create a new project on Kiel window and select the target.
2. Create a new file under the project and write the code.
3. Save the code with .c extension and add the file to the source group folder under the target folder.
4. Configure flash tools and create the hex file.
5. Compile the code by pressing F7.

Once the code is compiled and a hex file is created, next step is to dump the code into the microcontroller. Since here we are not using any hardware device, we simply use Proteus to dump the code. This is done by first drawing the circuit on Proteus and then adding the code to the microcontroller by right clicking on the device.

How Quiz Buzzer Circuit Works?

Once the circuit is powered, the compiler will initialize the stack pointer and the variables having the non-zero initial values and perform other initialization process and then calls the main function. It then checks if any of the buttons is pressed. In other words the microcontroller scans for any of its input pins at port P1 to be zero or at logic low level. In case pressed, the display function is called by passing the corresponding number.  The microcontroller then sends the relevant signals to the port connected to the 7 segment display.

The BCD to 7 segment decoding operation is not required in this case as direct values are send to the port pins or the input pins of the 7 segment display such that the corresponding LEDs start glowing and the number is displayed. Simultaneously, a high logic signal is also sent to the buzzer pin such that current flows through the device and the buzzer start ringing.

Applications of Quiz Buzzer Circuit:

1. This circuit can be used at quiz competitions organized at schools, colleges and other institutions.
2. It can be also used for other games.
3. It can be used as at public places like banks, restaurants as a digital token display system.

Limitations of Quiz Buzzer Circuit:

1. The microcontroller used is a CMOS device and is highly static and hence cannot be touched by bare hands.
2. It is a low range circuit, i.e. it is not possible to operate the circuit remotely.
3. It is a battery operated circuit and can easily run out of power once the battery life time ends.
4. It is a theoretical circuit and in practical application may require some passive components and even designing a linear power supply circuit to power the circuit directly using the mains supply.

source:http://www.electronicshub.org