Electronics Project: Sound level meter with audio announcement for library
As our final year project we are going to present “Sound level meter with voice announcement”. Our project measure sound pressure level and display it on 16*2 LCD. 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.