LIBRARY SILENCE MANAGEMENT SYSTEM. mechanical engineering projects pdf
As our final year project we are going to present “Library silence manager”. Our project measure sound pressure level. The project is also connected to Audio announcement circuit. So our project continuously measure sound pressure, and compare with critical noise level set using microcontroller programming. If sound noise pressure exceed from set value, voice announcement circuit start play, giving warning massage. This project can be very useful for the college library and everywhere where noise level matter.
A basic sound level meter shows the sound pressure level with different frequency weighting and with different time integration that are used for noise assessment. In almost all countries, the use of A-frequency-weighting is mandated for protection of workers against noise induced deafness.
The standard sound level meter is more correctly called an ‘exponentially averaging sound level meter’ as the AC signal from microphone is converted into DC by a root-mean square circuit and thus I must have a time constant of integration; today, referred to as time weighting. The output of RMS circuit is linear in voltage and passed through a logarithm circuit to give a linear readout in decibels. It follow that decibels is not a unit but simply a dimensionless ratio-in case, the ratio of two pressures. The decibel is a logarithmic unit used to describe a ratio. The ratio may be power, sound pressure, voltage, intensity, etc. Not at all frequency is equally loud. This is because human ear does not respond equally to all frequencies. Our ear much sensitive to sound in frequency range of 1 KHz to 4 KHz. So sound meter are usually fitted with a filter whose response to frequency is almost like that of the human ear. If the A-weighting filter is used, the sound pressure level is given in dB unit.
Condenser mic is used as an input device. The sound is converted into electrical signal using condenser mic. This signal is than amplified by using LM358.For sufficient amplification we are using two operational amplifiers. The audio output is received through pin 2 and feedback is given through VR1. Here VR1 is used to get an output amplitude level between 0 to 4 volts.
LM 358 is dual operational amplifier consisting of two independent, high gain, internally frequency compensated operational amplifier that are design specially to operate from a single power supply over a wide voltage range. Operation from split supplies also is possible if the difference between the two supplies is 3 V to 32 V and VCC is at least 1.5 V more positive than the input common-mode voltage. The low supply-current drain is independent of the magnitude of the supply voltage.
Applications include transducer amplifiers, dc amplification blocks, and all the conventional operational amplifier circuits that now can be implemented more easily in single-supply-voltage systems. For example, these devices can be operated directly from the standard 5-V supply used in digital systems and easily can provide the required interface electronics without additional +-5-V supplies.
This analog output is fed to the analog input of PIC microcontroller. The AVR microcontroller is used because it has internal analog to digital converter. Atmega 8 belongs to a class of 8-bit microcontrollers of RISC architecture. It has 8kb flash memory for storing a written program. Since memory made in FLASH technology can be programmed and cleared more than once, it makes this microcontroller suitable for device development. IT has data memory that needs to be saved when there is no supply. It is usually used for storing important data that must not be lost if power supply suddenly stops. For instance, one such data is an assigned temperature in temperature regulators. If during a loss of power supply this data was lost, we would have to make the adjustment once again upon return of supply. mechanical engineering design projects pdf
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