20-08-2012, 04:21 PM
SOUND LEVEL METER WITH AUDIO ANNOUNCEMENT FOR LIBRARY
1SOUND LEVEL.pdf (Size: 1.04 MB / Downloads: 311)
INTRODUCTION
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.
Working
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 PIC microcontroller is used because it has internal analog to digital converter. PIC16F877 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.
PIC16F877
The PIC16F877 is 8-bit microcontroller .The PIC16F877 Microcontroller includes 8kb of internal flash Program Memory, together with a large RAM area and an internal EEPROM. An 8-channel 10-bit A/D convertor is also included within the microcontroller, making it ideal for real-time systems and monitoring applications. All port connectors are brought out to standard headers for easy connect and disconnect. In-Circuit program download is also provided, enabling the board to be easily updated with new code and modified as required, without the need to remove the microcontroller. 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. 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.
Analog-to-digital converter module
The Analog-to-Digital (A/D) Converter module has five inputs for the 28-pin devices and eight for the other devices. The analog input charges a sample and hold capacitor. The output of the sample and hold capacitor is the input into the converter. The converter then generates a digital result of this analog level via successive approximation. The A/D conversion of the analog input signal results in a corresponding 10-bit digital number. The A/D module has high and low voltage reference input that is software selectable to some combination of VDD, VSS, RA2, or RA3. The A/D converter has a unique feature of being able to operate while the device is in SLEEP mode. To operate in SLEEP, the A/D clock must be derived from the A/D’s internal RC oscillator.
CAPACITORS
The capacitor's function is to store electricity, or electrical energy. The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC).
This symbol “ ” is used to indicate a capacitor in a circuit diagram. The capacitor is constructed with two electrode plates facing each other, but separated by an insulator. When DC voltage is applied to the capacitor, an electric charge is stored on each electrode. While the capacitor is charging up, current flows. The current will stop flowing when the capacitor has fully charged. However, in the case of alternating current, the current will be allowed to pass. Alternating current is similar to repeatedly switching the test meter's probes back and forth on the capacitor. Current flows every time the probes are switched. The value of a capacitor (the capacitance), is designated in units called the Farad (F).The capacitance of a capacitor is generally very small, so units such as the microfarad (10-6F ), nanofarad ( 10-9F ), and Pico farad (10-12F ) are used. Recently, an new capacitor with very high capacitance has been developed. The Electric Double Layer capacitor has capacitance designated in Farad units. These are known as "Super Capacitors."