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Key words: 1-Wire; single bus; home monitoring network; web server; TINI
Overview As people's living standards and housing conditions improve, the living environment and safety will also increase. The requirements for summarizing these aspects are collectively referred to as the home monitoring network. A complete home monitoring network should include security monitoring; environmental monitoring; smart home appliances; remote control and several major aspects of web servers.
For home monitoring network applications, there are already some solutions, mainly in the following three ways:
1) Wireless solution, where all monitoring units in the home are wirelessly connected to the host. The significant advantage is that there is no need to lay cables for network connections. However, there are also obvious disadvantages: each monitoring unit needs to be replaced periodically due to the use of battery power, which is susceptible to strong external electromagnetic interference and high cost;
2) Power carrier scheme, that is, all monitoring units in the home are connected to the host through power lines. This way, thanks to the existing cable, there is no need to re-route. However, there are many problems in the application of some low-cost power carrier communication methods in China, such as poor reliability. Moreover, after the power outage, the home monitoring network will be invalid;
3) The traditional wired communication scheme adopts the serial communication methods commonly used at present, such as RS-485/RS-422, CAN, and the like. Among them, RS-485/RS-422 is the most widely used and has relatively low cost. However, due to the need for microprocessor control, the cost is still relatively high compared to home monitoring network applications, especially when monitoring a single I/O; while CAN provides higher reliability while cost It is also higher than the RS-485/RS-422 communication solution.
In addition, these solutions also have a common shortcoming, that is, the lack of uniform standards, resulting in poor interoperability between monitoring units of different functions. In order to solve the shortcomings of the above schemes, this paper proposes a 1-WireTM single bus using Dallas Semiconductor as a solution for home monitoring network to solve the cost, standard and openness constraints in home monitoring network applications.
1-wire technical standard
The 1-wire single bus is different from most standard serial data communication methods, such as SPI/I2C/Micro-wire. It uses a single signal line to transmit both data bits and time-synchronized clocks for data bits, and the data transmission is two-way. of. Most 1-wire devices do not require an additional Power Supply and can draw sufficient supply current directly from a single bus (ie parasitic supply). The hardware interface for the 1-Wire single bus is shown in Figure 1.
Each 1-Wire device has a world-wide, factory laser-scaled 64-bit ROM ID code (with 8-bit CRC), which is a globally unique identification code of 256 different combinations. It can be used both as a product identity and as an address identifier in a multi-node application. Therefore, all home monitoring units using 1-Wire devices have a unique identification code and do not have to manually assign the physical address of the network. Access to 1-Wire devices requires a standard 1-Wire protocol that supports a normal rate of 16kBit/s and a high-speed mode of 142kBit/s. It is required to operate in strict order and timing. For details, please refer to the 1-Wire protocol standard.
1-Wire Product Features Although the functions of each home monitoring unit are different, they are composed of basic digital I/O, analog I/O, and storage units. Network expansion devices are also needed, as well as Web servers that support monitoring network access and connecting to the Internet. All microprocessors with programmable I/O ports can be used as 1-wire masters, with strict implementation of the 1-Wire protocol.
The 1-Wire home monitoring unit is built into a variety of home monitoring objects, but they can be composed of basic functional units, such as switching input/output, analog input/output, and monitoring of special functions. unit. The following sections discuss how to use the 1-Wire device to construct the functional units required in a 1-Wire home monitoring network.
1-Wire Digital I/O
The DS2405/DS2406/DS2408 can be used for digital signal input such as switch button status detection, door and window status, water leak detection, and gas leak alarm. The monitoring unit based on this type of device eliminates the need for local power or battery power and connects only two wires to the 1-wire bus, which solves the power supply and data communication, greatly simplifying system design, field wiring and system expansion. Figure 2 shows a typical 1-Wire digital input circuit (not limited to leak detection applications). In addition, the DS2405/DS2406/DS2408 can be used for open-drain outputs (such as controlling N-channel MOSFETs), non-contact electronic switches (such as controlling triacs), and holding digital outputs such as relays. When controlling zero-power devices, such as N-MOSFETs, holding relays, etc., there is no need for local power supply, and local power supply or remote power supply is required only when continuous power consumption is required. The 1-Wire digital output circuit is essentially identical to the 1-Wire digital input circuit. Its digital output can be directly or indirectly controlled by lights, household appliances switches, water heaters, door locks, etc. according to application requirements.
1-Wire analog measurement
The DS2438/DS2450/DS2760 can be used for analog measurements. In most analog monitoring applications, parasitic power can be used unless the associated sensor requires a large current.
Figure 3 shows the DS2438's 1-Wire humidity sensor with parasitic power. The voltage output of the humidity sensor is proportional to the supply voltage and relative humidity and is related to the ambient temperature of the operation. This requires measuring both the supply voltage of the sensor element and the output voltage of the sensor, as well as the temperature of the humidity sensor. Since the DS2438 has two built-in ADCs and one temperature sensor, which meets the above measurement requirements, the 1-Wire humidity sensor built by the DS2438 is very suitable.
1-Wire Analog Outputs Most of these applications can be designed with parasitic power to simplify design and reduce cost.
As a web server for a home monitoring network, a web server necessarily requires a low-power, low-cost design, so it is impossible to use a PC or a server as a home web server. The DS80C400 network microcontroller includes a 1-Wire master that provides Ethernet access control, built-in TCP/IP protocol, IPv4 support, and IPv6 for future use.
In an environment with an Ethernet interface, the DS80C400-based home monitoring network web server can be directly connected to the network. In addition, TINI's dial-up PPP protocol can be used to access the Internet through a modem connected to the RS-232 interface, a CDMA/GPRS module, or other communication device of the same function. Because TINI supports standard Internet protocols such as TCP/IPv4/v6, DNS, DHCP, HTTP, and FTP, it can pass any built-in browser and host devices that support Internet access, such as PC, laptop, PDA, Mobile phones, etc. After logging in with the necessary security password authentication, a two-way TCP connection between the home monitoring network web server and the host device is established, allowing the user to monitor the home environment and remote control home appliances on a familiar web interface.
The application example of the 1-Wire home monitoring network has now met the conditions for designing a complete and practical 1-Wire home monitoring network. All devices in the home can be detected, managed and controlled with other monitoring units such as 1-Wire digital I/O and 1-Wire analog I/O. Moreover, TINI is used as the web server of the home monitoring network, which allows the user to conveniently browse the indoor environment and equipment on the graphical web interface through the portable device or the PC terminal, and perform remote adjustment and control. Figure 4 shows a more complete application of the 1-Wire home monitoring network.
Conclusion
1-Wire is a simple, low-cost, addressable single bus. All 1-Wire devices adhere to the 1-Wire standard protocol, ensuring compatibility with all 1-Wire-based home monitoring units. Therefore, 1-Wire technology is more suitable for home monitoring networks, and has broad application prospects and promotion value. â–
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3.2 Standard type: usually used as indicator light, with half value angle of 20 °~45 °;
3.3 Scattering type: This is an indicator light with a large angle of view. The half-value angle is 45 °~90 ° or more, and the amount of scattering agent is large.
4. Classification according to the structure of LED
4.1 According to the structure of LED, it is divided into full epoxy encapsulation,
4.2 Metal base epoxy encapsulation
4.3 Ceramic base epoxy packaging and glass packaging.
5. Classification by luminous intensity and working current:
5.1 LED with ordinary brightness (luminous intensity 100mcd) is divided according to luminous intensity and working current;
5.2 The luminous intensity between 10 and 100 mcd is called high brightness LED.
5.3 The working current of general LED is between 10 mA and 10 mA, while the working current of low current LED is below 2 mA (the brightness is the same as that of ordinary LED).
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