Design of intelligent residential home control device based on LonWorks network

1 Device hardware design
1.1 Hardware function planning
The functions realized by the intelligent residential home control device include: monitoring the residential room environment (temperature, humidity); realizing remote billing for the three meters (water meter, gas meter, and electricity meter) of the residents; realizing three protections for the residents (fire prevention, gas leakage prevention, and theft prevention); realizing timing control of kitchen equipment; and realizing automatic exhaust control for the bathroom. Each device can be used as an intelligent node, and multiple nodes constitute the intelligent community management network system (i.e., LonWorks network). Setting up a server in the community center can realize the management of the entire network. In addition, home computers can communicate with home control devices to realize the management of indoor equipment.
1.2 Overall hardware design plan
Based on the above planning of the device functions, the device can be divided into two parts, namely, the Lon control module design and the acquisition module design. The control device takes the Lon control module as the core, and completes the various functions of the device by acting on various signals collected by the acquisition circuit. The Lon control module includes neuron chip, memory, crystal oscillator, transceiver, etc.; the acquisition module includes I/O interface circuit, photoelectric isolation protection circuit, drive circuit, buffer circuit, holding circuit, latch circuit and A/D conversion circuit, etc.; the two parts are connected through an 18-pin dual-in-line board edge connector and a 6-pin single-in-line board edge connector, which conforms to the modular design and is easy to install and debug. The schematic diagram of the hardware device is shown in Figure 1.

1.3 Lon control module design
In the design of this module, the selection of neuron chips, allocation of memory, and configuration of communication ports are involved, which are introduced as follows.
1.3.1 Selection of neuron chips
Neuron chips include Neuron3120xx and Neuron3150. The two chips are basically the same in function, except that the 3120 chip contains 2k memory, which is mostly used in hardware structures with fewer functions and no need for memory expansion; while the Neuron3150 chip has 0.5k EEPROM and 2k RAM memory inside, which can be expanded to store information, and can be used to develop more complex application systems. This article selects the Neuron3150 chip as the core device of the development device.
1.3.2 Communication port configuration
The communication port of the Neuron3150 chip can be connected to a variety of transmission media interfaces (i.e., network transceivers) to achieve a wide range of transmission rates. At the same time, the configuration of various types of network transceivers also provides conditions for selecting different communication media. The home control device in this design uses an FTT-10 transceiver configuration and uses twisted pair cables to transmit information with home computers and the entire community management network. The FTT-10 transceiver uses transformer isolation to achieve high isolation and high anti-interference. Its transmission distance can reach 2700 meters and the transmission rate can reach 78 kb/s, which can meet the requirements of information transmission between the device and the host computer. The communication port of the Neuron3150 chip can be configured into three working modes: single-ended working mode, differential working mode, and dedicated working mode. The pin definitions corresponding to different working modes are different, as shown in Table 1.

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The communication port of Neuron3150 chip in this device is configured in single-ended working mode, and the configuration of FTT-10 transceiver is shown in Figure 2, where the CLK end of FTT-10 is connected to CLK2 of 3150 to ensure the timing consistency of the two.

1.3.3 Memory allocation and circuit design
Since the internal memory of Neuron3150 chip cannot meet the storage requirements, in the design of Lon control module, external 32k flash memory and 24kSRAM are used as external memory, of which 16kB (addressing range 0X0000-0X3FFF) flash memory is used to save Neuron3150 chip firmware, and another 16kB flash memory (0X4000-0X7FFF) is used to store various configurations and application information. 24k SRAM is mainly used to store application data and cache of network data packets. The memory allocation diagram is shown in Figure 3:

In the circuit design, the A15 port of the 3150 chip is used to realize the chip select of the 32k flash memory (low level is valid), and the result of the NAND operation of A14 and A13 of the 3150 chip is used to drive the chip select of the SRAM (low level is valid). The specific circuit design is shown in Figure 4.

1.4 Collection circuit design
According to the functions to be realized by the device, the collection circuit is planned to be 12 digital inputs, 12 digital outputs, and 4 analog inputs: the I/07 to I/0010 pins of the Neuron3150 chip are used to receive the indoor temperature and humidity values, configured as a 4-channel analog circuit; the I/OO to I/O-6 pins and the 3-channel I/O ports expanded by the address bus together form 24 digital signals.
1.4.1 Analog input circuit design
The analog input circuit is designed to detect the room environment (temperature, humidity), and the circuit is shown in Figure 5.

The Max186 chip in the figure is used for A/D conversion. It is produced by Maxim Corporation of the United States. Max186 is a 12-bit data acquisition integrated chip. It combines 8-channel multiplexers, large bandwidth tracking/holding circuits and serial interfaces. The 4-wire serial interface can be directly connected to SPI, QSPI Microwire devices without external logic, and uses internal clocks or external serial interface clocks to complete successive approximation analog/digital conversion. The analog input signal entering the chip through the emitter follower is a 0-5 V voltage signal, which can be converted into a digital signal and serially enter the neuron chip in the form of Neurowire bus, and then stored in the memory SRAM. These data can be transmitted to a home computer for display and recording.

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1.4.2 Digital circuit design
Digital circuit design includes input circuit design and output circuit design.
(1) Digital input circuit
The digital input circuit is designed to collect three-meter and three-protection signals. The circuit is shown in Figure 6. The digital input circuit is based on the 6-bus expanded by the I/OOI/O-5 pins in the neuron chip, and forms 12 channels through the chip selection signal. The photoelectrically isolated input end of this circuit is connected to various sensor signals to prevent the components from being burned due to excessive sensor input voltage. Two 74LS245 chips are used as digital input buffer circuits to ensure that the device can accurately receive sensor signals.

(2) Digital output
circuit The digital output circuit is based on the 6-bus extended by the I/OOI/O-5 pins, and forms 12 channels through the chip select signal. The circuit is shown in Figure 6. The two 74LS273 chips in the figure are used as output latch circuits. The circuit maintains the input state, so that the output signal of the Lon control module can be reliably transmitted to various actuators.
1.5 Anti-interference circuit design
In the hardware design process, a variety of anti-interference design measures were considered.
(1) Use a high-quality power supply to power the controller, connect the power supply at a single point, and connect the ground at a single point.
(2) The digital circuit and analog circuit on the circuit board are separated as much as possible, the digital ground is separated from the analog ground, and the ground wire and power wire are as thick as possible.
(3) The input signal is isolated by an optocoupler to prevent the backflow generated by the peripheral device from impacting the system circuit when it is in action.
(4) A discharge diode should be added to the relay coil of the digital output, and a resistor can be connected in series to soften the signal transition edge or provide a certain amount of damping.

2 Program Design
The above functions are modularly designed in the application, mainly including remote meter reading module, alarm linkage module, indoor environment monitoring module, and sequence control module. Each functional module is driven by timer events. The program flow chart is shown in Figure 7:

3 Conclusion
This device can be used to control the temperature and humidity of the house to meet the standards of smart houses (temperature is controlled at 18-28℃, humidity is controlled at 30-70%); this device can accurately collect various information and issue commands in a pre-set manner to achieve three protections (fire, theft, and gas), monitor kitchen cooking utensils and bathroom exhaust, and three-meter billing functions; this device can accurately transmit the information collected by the three meters, the indoor temperature and humidity values, and the status of indoor equipment to the home computer, and the home computer can monitor the work of the control device.