Basically the circuit works on two oscillator HF and LF. An oscillator is used to produce periodic or regular repetitive waveform in the form of sine, square, saw tooth or triangular waves.Low frequency oscillator produces waveform at very low frequency generally in the range of 0 – 20 Hz. In this circuit we are using it to modulate the pitch of audio amplifier. In this circuit HF oscillator is formed using N1, N2 along with VR1, VR2, C1 and C2 in free running astable multivibrator mode and LF oscillator is made with the help of N4, N5, VR3, VR4, C3 and C4. In this circuit N3 and N6 are utilizing as buffer.
8 player quiz buzzer can be used in various competition organise in school and colleges to identify the team who has pressed the buzzer first. Advantage of this circuit is once a team has press the switch others are not allowed to press the switch therefore it block other participant. So with the help of this circuit you can easily identify the contestant who has press the switch first. You can use variable power supply ranging from 6V to 15V. You can provide power supply with the help of adapter readily available in market or you can make your own power supply with help of transformer and bridge rectifier. This simple circuit is based on one IC namely 74LS373 with few more easily available components. 74LS373 is a 3 state octal D type transparent latch and edge triggered flip flop.
Piezo buzzer is an electronic device commonly used to produce sound. Light weight, simple construction and low price make it usable in various applications like car/truck reversing indicator, computers, call bells etc. Piezo buzzer is based on the inverse principle of piezo electricity discovered in 1880 by Jacques and Pierre Curie. It is the phenomena of generating electricity when mechanical pressure is applied to certain materials and the vice versa is also true. Such materials are called piezo electric materials. Piezo electric materials are either naturally available or manmade. Piezoceramic is class of manmade material, which poses piezo electric effect and is widely used to make disc, the heart of piezo buzzer. When subjected to an alternating electric field they stretch or compress, in accordance with the frequency of the signal thereby producing sound.
The quiz buzzer systems are widely used in school, colleges and TV programs. The team which presses the buzzer earliest is entitled to give the [[wysiwyg_imageupload::]]answer. At times it becomes very difficult to identify which team has pressed the button when two teams press the buzzer within a very small time gap. In such cases the decision can be biased due to human intervention. The quiz buzzer presented here takes care of the aforesaid problem. This quiz buzzer disables the other inputs as soon as the first buzzer is pressed. This quiz buzzer can be used for a maximum of eight teams. It is build around 8051 microcontroller (AT89C51). This quiz buzzer system has eight input pins corresponding to eight teams. The output is displayed on a seven segment display (interfaced with microcontroller), which shows the number corresponding to the team which has pressed the button first. A buzzer is also sounded for a small duration to give an acoustic alarm. The connections of the seven segment, input pins and output pins is shown in the circuit diagram.