Announcemnt systems are rapidly getting popularity these days becuase no body has time to read news paper or attend any meeting. In the school or college students may get their result announcemnt on the cell phone or any important information as an accounement. Basically it is the system used PIC Microcontroller send sms to the subscriber about any particular annoucement. System reads the sms and announce this on the speaker. This way speaker can send his message through sms to the targetted audience.
The purpose of this project is to light an LED at a central monitoring station that corresponds to a specific speaker, if the speaker is still connected properly in a public address system. The following design requirements were set at the beginning of this project.
• To be compatible with existing public address system hardware. Competing technologies require specific audio amplifiers with network interface cards.
• Capable of being installed in an existing two wire public address system. Installing additional wiring to each speaker would be very costly.
• No batteries to be installed at each speaker, Maintenance cost of replacing batteries at each speaker would be very costly.
The topic of supervision of public address systems due to fire and building codes is becoming more prevalent as codes become more stringent on the topic.The basic design concept is to install monitoring boxes at the end of each string of speakers which would be tuned to 20 kHz. In the absence of an announcement taking place a 20 kHz pilot tone would be sent out onto the lines and the impedance would be measured at the amplifier. If the current changed by ±5mA indicating a fault in the line an alarm would be sent to a GUI via cobranet. This design would make sense if all the speakers were wired in a straight line .The basic operation of the speaker supervision test follows this sequence:
1. Basic Stamp powered on begins test, Power also sent to Speaker Modules.
2. Basic Stamp outputs digital high on PO changing state of DPDT Relay #1 allowing the Basic Stamp to cease the line.
3. Basis Stamp outputs Speaker Module #1 frequency, if still connected properly returns digital high on speaker supervision line.
4. Basic Stamp receives digital high, activates LED that corresponds to speaker #1
5. Basis Stamp outputs Speaker Module #2 frequency, if still connected properly returns digital high on speaker supervision line.
6. Basic Stamp receives digital high, activates LED that corresponds to Speaker #2
7. Basis Stamp outputs Speaker Module #3 frequency, if still connected properly returns digital high on speaker supervision line.
8. Basic Stamp receives digital high, activates LED that corresponds to Speaker #3
9. Test Complete, Basic Stamp powered down therefore outputting digital low on PO changing state of DPDT Relay #1 allowing the public address system audio amplifier to cease the line.
This relay is used to switch from the audio amplifier having control of the line to the BS2 controlling the line. Once the speaker supervision test is initiated using the pushbutton on the BS2, Pin PO will be set using the high command which will automatically place the pin in output mode and place a +5 voltage level on the line. This command will turn Transistor #1 on allowing current to pass through the coil of the relay creating a magnetic field which will switch the state of both poles of the relay. Public address system with multi-point microphone input facilities and provisions for background music.
.1 Microphones, Generally: dynamic, omni-directional and as follows:
.1 Output Level at 1 kHz, Open Circuit: 81 db.
.2 Power Level: 60 db.
.3 E1A Sensitivity: 153 db.
.2 Wall-Mounted Microphones:
.1 Mounting: flush, on standard single gang wall box, rubber shock mounted.
.2 Finish: brushed chrome.
.3 Switch: double pole, double throw pushbutton for push to talk and line shorting.
.4 Frequency response: 100-10,000 Hz.
.5 Impedance: 150 to 200 ohms,
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