Design of remote wireless monitoring system for cooking fume based on GPRS

Abstract: Remote wireless monitoring of oil smoke is realized by using GPRS. The monitoring system uses AVR single-chip microcomputer as the control core. It collects the signal of oil smoke gas sensor TGs2100 and sends it to the server PC of the monitoring center through GPRS and Internet, so as to realize remote real-time detection of sensor signal; the control command sent by the monitoring center is received by the single-chip microcomputer through the wireless network and controls the external equipment according to the signal, so as to realize wireless control. Compared with traditional monitoring methods, this system has the advantages of low cost and convenient use, and has broad application prospects.
Keywords: GPRS; AVR single-chip microcomputer; oil smoke sensor; data acquisition; remote wireless monitoring; TCP/IP protocol

Oil smoke can cause serious harm to the human body and the environment, and strengthening the monitoring and control of oil smoke has become the focus of people's attention. At present, most of the domestic oil smoke monitoring methods are on-site monitoring. There are few monitoring systems with remote signal transmission functions, and the monitoring efficiency is not high. With the rapid development of mobile communications, GPRS mobile data communication networks have covered all parts of the country. In addition to the characteristics of fast access, always online, and traffic billing, GPRS also has wireless connection to the Internet service, which provides convenience for remote wireless monitoring. This system uses AVR microcontroller as the control core to detect oil smoke gas, and with the help of GPRS technology, the data is transmitted through the GPRS wireless network and the Internet to achieve long-distance real-time monitoring and management of oil smoke.

l Working principle of the system
The AVR microcontroller is used as the main processing chip to realize the collection and transmission of sensor signals and the reception of remote control commands. The system functional structure block diagram is shown in Figure 1.

When the system is working, the analog signal collected by the oil fume sensor enters the A/D conversion interface of the AVR microcontroller after filtering and amplification. The microcontroller stores the collected data in the extended SRAM and transmits it to the GPRS module, and transmits it to the remote PC through the GPRS network and the Internet connection, and displays it on the data acquisition monitoring software. If the staff of the remote PC needs to control the system, the control signal can be sent to connect to the GPRS service through the Internet. After receiving the signal, the GPRS module of the system also stores the data in the SRAM. The AVR microcontroller reads the data from the SRAM, controls the output warning signal, and controls the relay to control the oil fume purification equipment to take oil fume purification measures.

2 System Hardware Circuit Design
The system hardware circuit is mainly divided into sensor signal acquisition circuit, storage circuit, GPRS module interface circuit, relay output control circuit and other parts.
2.1 Data acquisition circuit
The single-chip ATmega64L has a 10-bit successive approximation ADC with a sampling rate of up to 15 kSPS at the highest resolution, 8 multiplexed single-ended input channels, single-ended voltage input based on 0 V (GND), ADC input voltage range of 0~Vcc, optional 2.56 V ADC reference voltage, and ADC also includes a sample-and-hold circuit to ensure that the voltage input to the ADC remains constant during the conversion process.
The sensor used in the system is the TGS2100 air quality sensor, which has the characteristics of high sensitivity to odor gas and gaseous air pollution, low power consumption, long life, low price, simple application circuit, etc. It is widely used in gas measurement alarms such as cigarette gas, oil fume, odor, etc. The TGS2100 sensor circuit is shown in Figure 2.

Among them: VH is the voltage applied to the heating resistor RH to ensure that the sensor works at a suitable sensing temperature; VC is the working voltage of the sensor. VC and VH can use the same power supply to ensure 5.0±0.2 V DC: RS is the sensitive resistor. Its resistance value changes with the change of smoke concentration; RL is the load resistor. The voltage across it is the output voltage of the sensor. To ensure the accuracy of sensor detection, the power consumption Ps of RS is required to be ≤15 mW when the sensor is working.
2.2 Storage circuit
Since the Ethernet data packet can be up to 1500 B, when the data transmission peaks, the microcontroller cannot store it. Therefore, an extended RAM is used to improve the data throughput capacity of the entire system. Combined with the requirements of this system, the IS62C256 chip produced by ISSI is used. This is a low-power, 32 KB, 8-bit CMOS static RAM. Single power supply 5 V, TTL compatible input and output. Since the capacity is 32 KB, 15 address lines are required for control. In this system, the PA0~PA7 interface of the AVR microcontroller is connected to the high 7 bits of the IS62C256. During the reading and writing process, after the address is transmitted, the low 8 bits of the IS62C256 are latched, and then the data is transmitted.
In addition, the system also uses E2PROM to store some configuration information, such as IP address, clock initial time, etc., to prevent the loss of information after the system power is off.
2.3 GPRS module interface circuit design
The GPRS communication module of this system uses Siemens' MC39i, which has three data transmission modes of GPRS, USSD and CSD, as well as SMS and FAX functions. The module has the characteristics of small size, light weight and low power consumption.
According to the requirements of this system, the functional pins used only include power input, power ground, SIM card pins, control part and data input/output. The system uses a three-wire system (RXD/TXD/GND) to connect MC39i and the microcontroller. For the unused pins in the standard RS 232, if they are output pins, they are left floating, and if they are input pins, they are pulled up by a 10 kΩ resistor. The IGT pin of the module interface is used to start the GPRS engine module, which is enabled by the falling edge.
2.4 Relay output circuit module
The relay output is led out from the microcontroller I/O port, triggering the transistor to turn on the control relay, thereby controlling the operation of the external device. The relay output circuit is shown in Figure 3.

3 System software design
After the system is powered on and reset, the system must first be initialized, that is, its working parameters must be set to ensure its normal operation. It mainly configures some registers, such as the receiving configuration register, the sending configuration register, the data configuration register, the interrupt mask register, etc. The overall flow chart of the system software is shown in Figure 4.

When the system is working, it continuously sends AT commands to the MC39i module through the serial port to query whether there are new commands, and then performs relevant processing according to the commands.
On the PC of the monitoring center server, the data acquisition monitoring software uses VC++ as the development platform and TCP/IP Winsock programming
. The implementation of TCP is achieved through TCP API. By designing a TCP/IP port monitoring program on the PC, the system is controlled and communicated, and the TCP data packets sent by the system are monitored in real time to achieve the purpose of remote monitoring.

4 Conclusion This paper
discusses the use of AVR microcontroller as the main control core and GPRS technology to realize the remote wireless monitoring system of oil smoke. The system can not only be used for oil smoke monitoring, but also for signal monitoring in other fields, and has broad application prospects.