Development of Remote Intelligent House Control Device Based on ARM7

1 Overall design

As shown in Figure 1, the intelligent home appliance control system consists of a home intelligent control module, a home internal network system, and a GPRS module.

(1) Home smart controller: This part is the core of the system. It adopts embedded system design, can automatically run and process data, and manage and control the home system through RS485 bus. The controller also uses GPRS module to realize the communication between the home system and the external network, so that users can remotely control the home system through SMS and the Internet. At the same time, the controller also provides users with a human-machine interface through a keyboard and display screen, which is convenient for users to realize local control.

(2) Home system: The home system uses a single-chip microcomputer to form a number of small control systems to control various household appliances, and these small control systems are networked through a unified control bus, connected to a home intelligent controller, and controlled by the home intelligent controller.

The specific functions of the home intelligent controller system include:

(1) Data collection of household appliances: The data of the status of household appliances, including indoor temperature, lighting appliances, anti-theft doors, etc., is collected and fed back to the user after being processed by the controller.

(2) Local control: Users monitor home appliances through the keyboard and display on the controller.

(3) Remote control: Remote users can control and query the home system by sending text messages or through the Internet.

(4) Automatic alarm: When the controller detects an alarm signal such as illegal intrusion or excessive temperature, it will promptly trigger the indoor alarm device and notify the user by sending an alarm text message.

(5) Temperature query: Users can query the indoor temperature through the controller.

(6) Infrared home appliance control: Receive user commands and control infrared-controlled home appliances such as televisions and air conditioners through infrared transmitting circuits.

2 System Hardware Design

2.1 Hardware system structure

This article uses Samsung's S3C4480 chip as the central control module of the controller, which is responsible for communicating with GPRS communication module, home system module, data storage, keyboard, display and other modules, as well as data collection and processing of the system. It is mainly divided into two parts: home intelligent controller and home system.

2.2 Hardware Design of Smart Home Control Devices

The circuit design of the controller is mainly divided into the following modules:

(1) Peripheral circuit modules of ARM processor S3C44B0: including power management, keyboard, display, and data and program storage devices such as SDRAM and Flash.

(2) GPRS communication module and its peripheral circuit design: The GPRS module is used to realize data transmission between remote users and control terminals. This paper selects the MC35I module of Siemens. Its peripheral circuit design mainly completes the circuit design of the power supply part of the MC35 module, data transmission, module startup and shutdown, and working mode indication.

(3) Serial port expansion: GPRS modem dial-up Internet access requires the processor to provide a complete 9-wire serial port, but S3C4480 only provides a 3-wire serial port. Therefore, this paper expands the complete 9-wire serial port by connecting an external dual-channel universal asynchronous receiver and transmitter ST16C2550.

(4) RS485 converter: The RS485 interface chip 75LBCl84 from TI is used to realize the conversion between the TTL level of the S3C4480 (single-chip microcomputer) serial port and the RS485 level. The input impedance of this chip is twice the standard input impedance of RS485 (≥24kΩ), so 64 nodes can be connected on the bus.

2.2.1 Peripheral Circuit Design of ARM Processor

2.2.1.1 Use of development board resources

The development board provides a wealth of external resources. In addition to the necessary configurations such as power supply, clock source, reset circuit, etc., the following briefly introduces some of the resources used by the system:

External memory configuration: 2MB Flash, 8MB SDRAM, providing storage space for the storage and operation of system data, programs and operating system kernel.

Extended network port: 10M network port, RTL8019AS, this part is used to download the operating system kernel and application programs from the PC.

LCD interface (with LCD display): 320×240, STN, 16 gray levels, maximum 640×480256 colors.

Keyboard: The keyboard and LCD interface are used to provide the user with a local controlled human-computer interaction interface.

Serial port: Two standard RS232 ports. Used to connect to a PC and perform system debugging via a hyperterminal.

JTAG interface: JTAG emulator can be used to perform online simulation through the JTAG boundary scan port. Currently, there are two standards for JTAG, namely 14-pin interface and 20-pin interface. The development board uses the standard 14-pin JTAG interface, supports the full range of ARM7 processors, supports STD, parallel port connection, and supports network debugging function.

Buzzer: used as indoor alarm signal device.

2.2.1.2 System Memory Allocation

S3C44B0 supports big/little end selection for data storage (selected through external pins); it has 8 memory banks, each of which can reach 32MB, totaling up to 256MB; the access size of all memory banks can be changed (8 bits/16 bits/32 bits); among the 8 memory banks, Bank0~Bank5 can support ROM and SDRAM; Bank6 and Bank7 can support ROM, SRAM and SDRAM, etc.; the starting addresses of 7 memory banks are fixed, and the starting address of 1 memory bank is variable.

The Flash in the development board uses SST39VFl60, 1M×16 bits, as a program memory mainly used to replace ROM, and can also store some important data when necessary. The SDRAM chip in the development board uses HY57V641620, 4M×16bit, with a storage capacity of 8MB. Use SDRAM as system memory.

2.2.2 GPRS module NC35 and its peripheral circuit design

2.2.2.1 MC35 module

MC35 is a new generation of wireless communication GPRs module launched by Siemens. It mainly consists of six parts: GSM baseband processor, GSM radio frequency module, power supply module (ASIC), flash memory, ZIF connector and antenna interface.

2.2.2 MC35 peripheral circuit design

(1) MC35I power supply circuit

The module requires a single power supply, providing a voltage of 3.3 to 4.8V (the standard input is 4.2V) and a current of 2A. This article uses LM2576ADJ to provide power for the module. The chip is a step-down switching voltage regulator with an input voltage range of 10 to 40V. It uses a 12V input (obtained through a 220V to 12V transformer) and an output of 4.5V. The power supply circuit design is shown in Figure 2.

(2) Startup and shutdown circuit

The startup circuit is composed of an open-drain transistor and a power-on reset circuit. This paper uses program control to implement it. Its circuit diagram is shown in Figure 3, and its simplified circuit is shown in Figure 4.

The first method is manual control. The circuit is shown in Figure 3. It is mainly used for separate debugging of the MC35I module. When S1 is pressed, the base of Q3 is at a high level, Q3 is turned on, and the voltage of the IGT pin is pulled down to start the module.

The shutdown circuit gives this pin a low level of more than 3.5s through the transistor, which can shut down the GPRS module. The circuit design is similar to Figure 3.

2.2.2.3 Data communication circuit

In terms of electrical characteristics, the serial port of the MC35 module uses the ITU-TV.24 protocol, which is not compatible with the RS232 level. Therefore, level conversion is required.

In this system, we use TI's MAX3238 level conversion chip. The data communication circuit design is shown in Figure 5.

2.2.2.4 SLM card circuit

MC35I also provides 6 SIM card circuit interfaces. The circuit connection diagram of the SIM card reader is shown in Figure 6:

2.2.3 Serial port expansion module

In order to realize the network remote control of the home intelligent controller, it is necessary to dial up to the Internet through the GPRS modem MC35. This design uses AT's ST16C2550 to complete the serial port expansion. The circuit connection diagram of ST16C2550 and ARM processor is shown in Figure 7.

In addition, the serial port output of ST16C2550 is TTL level, and MAX3238 is used here to convert the level into RS232 level of the serial port.

2.2.4 RS485 interface circuit

The home intelligent controller designed in this system uses RS485 bus for the internal network wiring of the home. Since neither the ARM processor 44B0 nor the single-chip microcomputer (AT89C52 from Atmel Company selected in this article) provides a ready-made RS485 bus interface, it is necessary to select a conversion chip to realize the interface conversion. This system uses a RS485 interface chip 75LBC184 produced by TI Company.

2.2.4.1 RS485 interface circuit design

The serial port outputs of 44B0 and the microcontroller are both TTL level, so the connection circuits of 44B0, the microcontroller and 75LBC184 are consistent, and the circuit diagram is shown in Figure 8.

2.3 Home System Module

The home intelligent system integrates home appliance control, security, entertainment and leisure and other functions. This article implements infrared home appliance control and temperature alarm modules in the home system module. Each module is composed of a single-chip microcomputer as a controller, and is connected to the RS485 bus through the single-chip microcomputer to form a home network, and is ultimately controlled by the home intelligent controller.

2.3.1 Infrared home appliance control module

Infrared home appliance control modules are mainly used to control home appliances that contain infrared receiving chips.

2.3.1.1 Design of infrared emission circuit

The infrared emitting device used in the infrared emitting circuit is the plastic-encapsulated TSAL6200 infrared emitting diode. The width and interval of the infrared pulse train are controlled by the time interval of the high and low levels output by the single-chip microcomputer through the I/O port. The modulation circuit is a controllable oscillator composed of two monostable triggers U2A and U2B cascaded from 74LS123. The circuit diagram is shown in Figure 9.

2.3.1.2 Design of infrared receiving circuit

The infrared receiver uses HS0038B infrared receiver, and the circuit design is shown in Figure 10.

2.3.2 Temperature alarm module

Temperature testing and alarm devices are very necessary in household appliances. Many household appliances can read temperature signals through intelligent controllers for autonomous adjustment. When an emergency such as a fire occurs indoors, the temperature test can be used to send an alarm signal to the user in a timely manner to take action.

The temperature sensor is a single-line digital temperature sensor chip DS18B20 from Dallas. The circuit design is shown in Figure 11.

3 System Software Design

The software design of the system is mainly divided into three parts: software design of the home system module, RS485 communication protocol design, software design of the home intelligent controller and the home system communication, and software design of the home intelligent controller. Among them, the software design of the home intelligent controller is the core of the system software design. The software design of this part uses the embedded u Clinux operating system as the development platform, which is responsible for data collection and data processing of the home system, and can communicate with remote users to achieve remote control. It is the key to realize the intelligent management of the home system. The software structure diagram of the system is shown in Figure 12.

4 Conclusion

This device can be used to control parameters such as residential temperature to meet the standards of smart homes (temperature control at 18-28°C); it can organically combine home appliances, anti-theft systems, and water and electricity systems to achieve intelligent management of home appliances and various subsystems. At the same time, it can achieve remote monitoring of home systems through text messages and other means.