Quiz Buzzer Circuit using 8051 Microcontroller and 555 Timer

Quiz buzzer systems are mostly used in schools, colleges and also in live quiz competitions broadcasted via television. A Quiz buzzer allows any user to press the switch quickly in response to a question posed during competitions that are conducted in schools and colleges. The pressed switch gives a buzzing sound or alarm for some duration of time and the reaction time is very small. Buzzers can also be used in different applications such as annunciator panels, electronic metronome microwave ovens, and other household applications.

Quiz Buzzer
Quiz Buzzer

A Quiz buzzer circuit can be implemented in several ways with the use of various controllers. These controllers include 555 timers and microcontrollers. The 555 timer based buzzer circuit is a simple and low-cost device wherein the time duration is determined by the resistor and capacitor values (RC constant). A Microcontroller based buzzer circuit is a programmable timer wherein the time duration can be varied by changing the program code of the microcontroller. The following description of both these circuits will help you to compare both the circuits and their operations.

Buzzer Circuit Using 555 Timers

A timer can be operated in three modes such as monostable, astable and bistable for multivibrator circuits. The timer is used for generating pulses using pulse modulation technique. In a monostable mode, the output is set to high for a certain time period determined by the RC time constant when the timer is triggered at pin 2. In a bistable mode, the triggering input is connected at pin 2. When the triggered input is low, the output of the circuit will be in a high state. The reset button is connected at pin 4, and if the input is low, then the output is also in a low state.

Buzzer Circuit Using 555 Timers
Buzzer Circuit Using 555 Timers

As shown in the figure, the buzzer circuit consists of a couple of resistors, capacitors and 555 timers which are set up as astable multivibrators. In an astable mode, there is no stable state and the pulses are generated at a low and high state in square waveform without any help from the user. This mechanism can be used in switching the flash lamps and LEDs.

Circuit Connections: In this circuit, the resistor R1 is connected between Vcc and discharge pin 7. Another resistor R2 is connected between the discharge pin 7 and the trigger pin2. The Pin2 and the threshold pin6 are shorted and connected through a capacitor. This capacitor charges through resistor R1 and R2 and discharges through R2. The Pin1 is connected to the ground for negative biasing, and the pin 5 is connected to the ground through the capacitor, and the pin3 is used as an output. The Pin 7 is connected to the potential divider of R1 and R2 resistors.

Circuit operation: This circuit is in astable mode which itself triggers and changes its states automatically from ‘High to Low’ and ‘Low to High’. When a switch is pressed, then the output at pin 3 is high during the capacitor charging from a power supply VCC through resistors R1 and R2. This capacitor gets charged up to 2/3 Vcc so that the output becomes high through this period and the speaker makes the sound. Then the capacitor starts discharging through resistor R2 till 1/3 Vcc, and the output at pin3 becomes low during this time so the speaker gets muted and completely gets turned off when the switch opens. This process repeats until the square pulses are generated from high to a low state and low to high state based on the RC time constant.


The quiz buzzer circuit with 555 timers can be further developed by using 8051 microcontrollers (AT89C51). In a 555 timer, the time value of the buzzer can be varied depending on the capacitor’s value, by using an 8051 microcontroller – the timing values can be changed by changing the program in the microcontroller. To understand this concept better, a practical example of a quiz buzzer that uses an 8051 microcontroller is given below.

8-Candidate-Quiz Buzzer with an 8051 Microcontroller (AT89C51)

This proposed 8 candidate quiz buzzer system is used in quiz competitions of schools and colleges. The team that presses the buzzer first is given the first preference for answering a question. Sometimes it is very difficult to recognize which team has pressed the buzzer within an infinitesimally small period of time. Coincidentally, if two team players press the buzzer at the same time, then the small time gap condition arises, which can be influenced by taking the opinion through the intervention of human beings.

This system is designed by using AT89C51, which is of 8051 family. This quiz buzzer is designed for a maximum of eight teams. In this system, we can go through the circuit operation and how the buzzer works.

Quiz Buzzer with an 8051 Microcontroller
Quiz Buzzer with an 8051 Microcontroller

Circuit Connections: This microcontroller consists of 40 pins, in which 32 pins are used for input and output purpose. In this system, total nine input pins are used, all the eight input pins are connected as switches to the port1 of the microcontroller, and the ninth pin is set as a reset button for resetting the buzzer system. The eight switches are connected to the buzzer; if any of the switches is pressed, then the buzzer gets blown. A Seven-segment display, which displays the information of the switch that is being pressed, is interfaced with the port 2 of the microcontroller. The microcontroller is programmed in such a way that if any switch is pressed, then the corresponding switch number is displayed on the LCD. The Power supply is connected to the 40 and 31 pins of the microcontroller and the buzzer.

Circuit Operation: When we press any push button from a set of push buttons connected to the port1, then this enables the corresponding pin to logic high. This transition of the signal from low to high at a particular pin enables the microcontroller output logic high for a certain time period. The microcontroller is programmed in such a way that it continuously scans the input pins and correspondingly makes a low path for the buzzer circuit and also displays the number on the seven- segment display corresponding to the input pressed.

The time period of the buzzer can be changed by modifying the microcontroller program with the desired time period. Generally, a microcontroller is programmed with embedded C language in Keil software.

This is all about the Quiz buzzer project designed and developed for 8 teams by using an 8051 microcontroller. We hope that you have got a better understanding of this topic. Furthermore, for any help regarding this topic, you can contact us by commenting in the comment section given below.

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