Based on smoke detection fire alarm system (Figure) - automatic fire alarm, fire alarm, equipment and equipment - Fire Industry
Abstract: Discussed with the MC14468 ionic smoke detection alarm, MCU 8051, nRF401 Single Chip RF transceiver composed of automatic fire alarm system. Since the introduction of wireless communication technology and FSK (Frequency Shift Keying) modulation and demodulation technology as the core of nRF401 RF transceiver, the system performance greatly improved, especially to make the system more real-time alarm and reliability.
Keywords: MC14468; 8051; nRF401; FSK; fire alarm
I. Introduction Floors of modern architecture is characterized by constantly heightening, mainly ease the shortage of land, from the perspective of, but also to consolidate power supply, heat supply, gas supply, easy centralized control and management. Now, whether general type (such as residential) or Deluxe (such as international hotels) and high-rise buildings, are increasing emphasis on fire prevention and safety technology to the application. Because of its floor more crowded, in case of fire, evacuation difficulties, fighting and difficult, will inevitably cause serious casualties and property losses. In order to protect the safe and reliable high-rise building must be designed with high reliability and good real-time automatic fire alarm and fire fighting system, its requirements are: (1) When fire occurs, can be the fastest detection alarm, and can detect fire occurred in specific locations (a specific address code); (2) verified confirmed, can be timely informed of the fire department fire; (3) fault detection system itself should have its own features, such as the system under voltage alarm and self-test function to ensure the automatic alarm system functions well; (4) high anti-jamming ability, to prevent the occurrence of false alarms systems.
Present, although already there are several automatic fire alarm system, but most of them also belong to the offline mode, ultimately rely on people to contact the fire department, often as not timely warning and cause significant damage. If you can work directly online, will substantially reduce the property damage and casualties. We focus on this issue is an attempt to fundamentally solve the offline problem of signal transmission directly to the signal sent by wireless transmission technology control room or fire department, to the first fire-fighting purposes.
Second, the overall structure of the system
The system consists of two parts: detection transmitter and receiving control section, the structure shown in Figure 1 and Figure 2. Both the control of single, simple structure, easy to implement. As a result of nRF401 Single Chip RF transceiver, so as to achieve the purpose of wireless transmission, can quickly send alarm signals to facilitate the timely control of fire. Control transmitter and receiver test side chosen the market has matured, high-performance chip, its simple structure and easy to implement, reliable and practical. System constituted by the three co-chip, testing devices manufactured by the Motorola has a sound and light alarm circuit of the MC14468 chip, to achieve more parallel testing, with the external circuit can constitute more smoke alarm system, the application circuit in Figure 3 shown. Nordic wireless transceiver used by the U.S. company's new wireless communications based on nRF401 monolithic radio transceiver, which uses wireless communication and FSK (Frequency Shift Keying) modulation and demodulation techniques, frequency stability and strong anti-interference, non- required to encode the data, the external circuit is simple, easy to use, its 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, no need to apply for permits. nRF401 introduction is one of the salient features of this system, it greatly improves the system's real-time, this security system is very important. SCM 8051, it is not only the MC14468 and nRF401 bridge between the play also control the chip clock cycle, the role of complement each other, and this is a very important part. Since the overall system structure is simple and easy to implement the software, so no special extension 8051.
Test transmitter and receiving control section
Detector NRF401 circuits 3, transmitter MC series chip MC14468 was Ionic Smoke Detector alarm chip, is currently on the market a very popular set of fire detection and alarm in one of the smart sensor. When detected when smoke particles, which can drive the external connection piezoelectric ceramic or piezoelectric buzzer alarm speaker sound, meantime, also drive light-emitting diode (LED) to the frequency of 1Hz flashing light, use of sound and light smoke alarm to alert the best results.
MC14468 1 foot (test output) directly connected microcontroller INT0, when smoke is detected, its output of high INT0 SCM through the work of the internal timer T0, time 90ms, T0 overflow interrupt into the interrupt service program, through the serial port to send data (room number or before a meaningful code of the system) to the single-chip radio transceiver nRF401. When it detects smoke, MC14468 own voltage 100mV of hysteresis to prevent other external factors (such as insects) caused by false alarms, combined with microcontroller generate 90ms delay, can improve the reliability of the system. T0 remember the beginning of each time, to re-set the initial value by the software, which is not as 90ms during the MC14468 pin 1 on the signal disappeared or become the next running low and lead to error.
NRF401 serial port directly connected to serial port (DIN connected TXD, DOUT connected RXD), TXEN end of the high / low set by software, can be realized nRF401 launch mode and receiving mode switching between . When you need to launch data, generated from the 4MHz crystal oscillator circuit as its internal PLL frequency reference frequency by N PLL and VCO for frequency doubling, the center frequency f0 as 433.92MHz or 434.33MHz (double channel), modulated, f = f0 ± f = f0 ± 15kHz (The chip modulation is ± 15kHz), the final amplified by power amplifier fired out from the PCB antenna.
4, receiving some
NRF401 received from the PCB antenna on the FM signal, microcontroller set TXEN is low end, PA is turned off to enter the receiving state. FM signals were amplified by low noise amplifier, mixer through (its role is to offset the plane between the transmitter and the receiver high-frequency interference) into IF, and then the band pass filter and the modulator, after demodulation, a data output. Then switch to launch single chip mode, the loopback handshaking signals, nRF401 to the data transmission to the microcontroller, after treatment from the P1 port output to LED display (fire source
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