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Based on the smoke detection system alarm fire (see Figure) – Automatic fire alarm, fire alarm, plant and equipment – Fire Industry

Summary: Review with the MC14468 ionic smoke alarm detection, MCU 8051, nRF401 a single chip RF transceiver integrated automatic fire alarm. Since the introduction of wireless communication technology and FSK (Frequency Shift Keying) modulation and demodulation technology as the core nRF401 RF transceiver, the system performance greatly improved, especially to make the system real-time alarm and reliability.

Keywords: MC14468, 8051; nRF401, FSK, fire alarm
I. Introduction The story of modern architecture is characterized by the continued escalation, mainly to easing the scarcity of land, from the perspective of, but also to consolidate the power supply, heat supply, gas supply, easy control and management centrally. Now, if the general type (such as residential) or Deluxe (Such as international hotels) and high-rise buildings are becoming more emphasis on fire prevention and safety technology for the application. Due to its crowded floor, in case of fire, evacuation difficulties, struggle and difficulties inevitably will cause serious casualties and property losses. In order to protect the high-rise building safe, reliable and should be designed with high reliability and the alarm of good real-time automatic fire fighting system, its requirements are: (1) When fire occurs, it may be the fastest detection alarm, and can detect fire occurred in specific locations (a specific address code), (2) confirmed checking can be timely informed of firefighters to the fire, (3) fault detection system should have its own characteristics, as the system of low voltage alarm and auto-test to ensure automatic alarm functions of the system and, (4) High anti-jamming capability to prevent the occurrence of false alarms systems.

Present, but and there are several automatic fire alarm, but most of them also belong to the online modality ultimately depend on people contact the fire department, often as not a quick note and cause significant damage. If you can work directly on-line, substantially reduce material damage and casualties. We focus on this issue is an attempt to fundamentally solve the problem offline direct signal transmission the signal from the control room wireless transmission technology or fire department, the first for firefighting.

Secondly, the general structure of the system
The system consists of two parts: the detection of the transmitter and the reception of the control section, the structure shown in Figure 1 and Figure 2. Both the control of the single structure, simple, easy to implement. As a result of a single chip RF transceiver nRF401 in order to achieve the purpose of transmission wireless, quickly can send alarm signals to facilitate the timely control of fire. control transmitter and receiver side chosen test the market has matured, the chip high performance, simple structure and easy to use, reliable and practical. System consisting of three co-chip, testing devices manufactured by Motorola has a circuit alarm light and sound of the MC14468 chip, to get more tests in parallel with the external circuit can be more than smoke detection system, the application circuit Figure 3 shows. Nordic wireless receiver used by new wireless communications company in the U.S. nRF401 based on monolithic radio transceiver, that uses wireless communication and FSK (Frequency Shift Keying) modulation and demodulation techniques, the frequency stability and strong anti-interference, not required to encode the data, the external circuit is simple, easy to use, the application circuit shown in Figure 4. As the low transmission power and high receive sensitivity of design, therefore, subject to restrictions on the Radio Regulations, without requesting permission. introduction nRF401 is one of the main characteristics of this system, which greatly improves real-time system, this security system is very important. SCM 8051, which is not only the MC14468 and nRF401 bridge between the work also control the chip clock cycle, the role of complement each other, and this is a very important role. Since the overall structure system is simple and easy to implement the software, so no special extension 8051.

Test the transmitter and the reception control section
Detector NRF401 circuits 3, MC Series transmitter chip MC14468 was Ionic smoke detector alarm chip, is currently on the market a very popular series fire detection and alarm in one of the smart sensors. When it detects when the smoke particles, which can drive external alarm connection piezoelectric ceramic piezoelectric speaker or buzzer sound, meantime, also the unit of light-emitting diodes (LED) at a frequency of 1 Hz flashing light, the use of smoke detectors light and sound to alert the best results.

MC14468 a walk (test output) directly connected to Microcontroller INT0 when smoke is detected, its production INT0 SCM discharge through the work of the internal timer T0, 90ms of time, T0 overflow interrupt in the interrupt service program, through port number to send data (room number or before a meaningful code of the system) for radio transceiver single-chip nRF401. When it detects smoke, MC14468 100mV tension inherent hysteresis to prevent other external factors (such as insects) caused by false alarms, combined with a microcontroller to generate 90ms delay, you may improve system reliability. T0 remember the beginning of each time, to re-establish the initial value by the software, which is not as 90ms for the MC14468 pin 1 on the signal disappeared or become the next running low and misleading.

NRF401 serial port directly connected to serial port (DIN TXD attached, DOUT RXD) TXEN end of the whole high / low for the software, you can do so nRF401 to launch and switch between receive mode. When you need to implement the Data obtained from the crystal oscillator circuit as its internal 4MHz PLL frequency reference frequency by N PLL and VCO to double the frequency, the center frequency f0 and 433.92 or 434.33MHz (dual channel), modulation, f = f0 f0 ± ± f = 15kHz (The chip modulation is ± 15kHz), the final amplified by power amplifier shot PCB from the antenna.

4, receiving some

NRF401 PCB received from the antenna in the FM signal, set TXEN is low-end microcontroller, PA off to enter the receiving state. FM signals were amplified by low noise amplifier, mixer through (its function is to compensate the plane between the transmitter and receiver high frequency interference) in SI, then the pass band filter and the modulator, after demodulation, a data output. Then switch to release mode single chip, the handshake signals loopback to nRF401 data transmission to the microcontroller, after the passage of the P1 port output LED screen (origin of fire About the Author

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