The MCU and Lonworks based Visual intercom system design (1)

Summary: introduces the intelligent community of the access control system, can be regarded intercom system design principles as well as hardware and software implementations; made for intelligent video intercom system solution.

Use the combination of SCM and Lonworks Visual intercom system that overcomes traditional 485 communication rate low, the communication distance is short of defects, increasing the system's bus and monitoring equipment compatibility.

　　

With the intelligent housing community, traditional Bell has far less able to adapt to modern families.

It is hoped that the adoption of a new way to understand the visitor, while ensuring their safety, reduce unnecessary trouble. Therefore all kinds of door bell quietly entered the millions.

From a simple tool to multifunctional Mengen Mody, General Electric, standard users are getting higher and higher, intercom system has become a modern multipurpose, efficient modern houses important protection.

With raw building intercom system, as well as urban residential area of construction and development, continual innovation. From the initial General Danyuanmen intercom, the Visual Danyuanmen intercom, to networking management, intelligent building intercom system has become a compatibility powerful integrated system. It can be said that the intelligent building intercom system is not only convenient for residents and visitors of the controlled door systems, and residential property management and security management essential to effective means, is a modern residential area essential facilities.

1 Lonworks bus technology

General Visual intercom system mostly by SCM and RS-485 bus, although the cost is low, but the restrictions by RS-485 bus, without relay, communication distance can not be too far away, communication rate cannot be too high, and the relay will increase the cost, increase the design development and construction of maintenance more difficult.

If you use simple Lonworks bus, and reduces network on other bus device compatibility, increase development costs and design problems. The author uses Lonworks based on-chip and the intercom technology, not only can overcome these shortcomings and be better able to play to the advantages of both. The entire system is the doorway Unit hosts and indoor Visual extension, on the network, depending on whether they are different communications node. In the common communication network, the node on the node to access the agreement is different, and for Lonworks network device communication, you only need to use a technique called LonTalk network standard language implementation. LonTalk Protocol consists of a variety of different devices on the network allowed each intelligent communication underlying protocol.

LonTalk Protocol is also known as ANSI/EIA709.1 control network standard that provides a range of communications services that makes your device applications to network with other device to send and receive messages without having to know the network topology, or a network of name, address, or other devices.

LonTalk Protocol can optionally provide end-to-end message confirmation, certified and priority of message to send to provide provisions restricted the number of transactions. To support network management service allows remote network management tools to network and interact with other devices, including network address and parameters of reconfiguration and download applications and report network problems and start/stop/reset device applications. Lonworks systems can communicate on any physical medium, including the power line, twisted pair, radio (RF) and infrared (IR), coaxial and fibre.

At the same time, LonTalk support in the communication media for hardware collision detection, LonTalk can automatically are colliding packets Cancel again.

If there is no collision detection, when a collision occurs, only get responses or answers when heavy transmitters. Lonworks is priority zone forecast p a stick CSMA algorithms to implement collision detection. Experiments show that 36 node on the Internet, using ordinary p a stick algorithm, when to be transmitted per second, Venda 500 ~ 1 000 package, collision rate by 10% to 54%; whereas the use of prediction p-stick CSMA algorithm in 500 Pack following collision rate is very low when in the 500 ~ 1 000 package, collision rate stable at 10 percent. In the network of the MAC layer to improve emergency response times, you must provide an optional priority mechanism that allows the user to each need priority node to assign a specific priority time slice (priority slot). In the send process, priority data packet will be sent within the time slice, the priority time slice can be divided into 0 ~ 127 any registration, low-priority node needs to wait a long time. This time slice in p a probability before time slice (i.e. the nodes of random wait time before), non-priority node will have to wait for the priority time slice is complete, then wait for the P-probability time slice and sent, so join the priority node has a faster response time, and thus better able to improve network utilization.

In the design of intelligent community, using Lonworks bus can use many of the control line and communications circuits integrated into cheap twisted pair, both saving development and construction costs, and facilitates the planning and management of the network.

2 system design

　　

For the entire Park, uses a star rating network; for larger community communication systems, you can use domain management.

Park network structure as shown in Figure 1.

　　

　　

　　

Figure 1 Park network chart

All nodes by AT89S52 microcontroller system and Neuron Chip TMPN3150B1AF constitute core modules, plus the FTT a 10A transceivers and the peripheral circuit.

Neuron Chip 11 I/O port that can be used by the software's flexible configuration 34 different interfaces, SCM strong realWhen the control has guaranteed real-time data transfer. The entire system is more than one network, subnetwork and child network expansion via Lonworks router. Each node via Lonworks bus for network communication, connected to each other to twisted pair, communication rate of 78 kb/s, video intercom system for video and audio through the simulated signal audio bus transport. The programme uses the 2-level bus design, realized in the same system at the multiple calls of the function. At the same time, set the network data management and data servers, real-time control of the network and the computer network for information sharing.

3 node hardware design

Node hardware design is by SCM and Lonworks joint control.

Node hardware schematic diagram shown in Figure 2.

　　

　　

　　

Figure 2 node hardware schematics

(1) CPU。

Node CPU use industrial grade AT89S52 and Neuron Chip family TMPN3150B1AF, 3150 chip without program storage space, hence the need to add external RAM, storage including LonTalk Protocol, Neuron C library function and Task Scheduler's system map, including Neuron C compiler-generated user application code, and other application-specific parameters of images. 3150 chip 11 application I/O pin, the pin can be configured in various ways and to provide a minimum spread circuit of flexible I/O functionality is available through the software set to 34 optional way of working. In this system, set it as a way 2, also known as output (bit output) to control relays consisting of audio switcher.

(2) transceiver.

Selection of Echelon Corporation FTT-10A, communication rate of 78 kb/s, coupled with the isolation transformer and a Manchester encoder, supports multiple network topologies.

(3) the program memory.

Selection of Winbond company W27C512 — 45, you can easily use to directly download the LonMaker application mappings, its large capacity for future extensions.

As a result of the microcontroller and Lonworks technology approach, not only compatible with the indoor traditional monitoring equipment, and improved network efficiency of communication and transmission rate, simplifies the whole system, reduces the possibility of hardware errors, improves the reliability of the system, greatly reduces the workload of hardware design.

In workflow, on the one hand, when an exception occurs within the household, such as generating more than normal concentration of smoke as well as Windows and doors are opened improperly, the monitoring equipment such as the acquisition of appropriate monitoring signal will be sent indoor Visual extension, 51 chip judgment sending Neuron Chip after processing, after transceiver on the Lonworks network, and transmitted to the Central Administration for the display and alarm, in order to facilitate community managers to take timely action in response; on the other hand there are visitors through cell host sends a request to indoors, you start the host CCD camera, and makes the corresponding video switch pick-up, will be guest images real-time delivery to indoor Visual extension of the display, convenient household identification.

When heads up and the door the host is connected to the electromagnetic lock, cut video, released on line resources for other visitors to use.

4 node software design

　　

4.1 Lonworks section

Neuron Chip for Neuron C programming language, it is derived from the ANSI C and ANSI C for deletion and updating.

For example, the Neuron C from events to drive the execution of tasks; Neuron chip provides milliseconds, and second the 2 types of software timer.

The main process as shown in Figure 3.

Its main tasks are as follows: first timer I/O objects and software and to set the variable definition of the initial value, determine whether there are "unlocked" signals, and starts the timer start timer, the Timer ends, Neuron Chip to accept the new scheduled task.

　　

　　

　　

Figure 3 main program flowchart

Neuron Chip (neuron chip) is at the core of Lonworks technology, it is the one with multiple processors, read-write/read-only memory (RAM/ROM) and [1] [2]