A simple circuit for transmitting information over low-voltage power lines. Transmission of control signals via the power bus

After reading the following material, the joke about the “Ethernet card killer,” which is a patch cord with an RJ-45 plug at one end and a 220 V network plug at the other, will no longer seem so witty. True, you will need to connect the appropriate PowerLine adapter to the break in this wire...

The famous joke that most inventions come from human laziness applies very well to data networks. Since communication between computers in the office became mandatory, and Ethernet became the de facto standard, there have been ongoing attempts to make this communication even easier - for example, by eliminating the need to lay additional cables.

We have already written more than once about various technologies that allow you to “save” on the wiring of a separate network infrastructure - for example, about HomePNA, which involves the use of telephone wiring, or about wireless networks of the Wi-Fi / 802.11x standard. The technology that will be discussed today uses to build local networks... ordinary electrical wiring that exists in any building.

PowerLine technology has a complex and changeable fate. Several times it was predicted to have a central place in the development of home information networks. Then they “forgot” about it, so that as the technological base improved, they came back again and proclaimed it almost a panacea. Neither research agencies nor IT publications have paid attention to this sector of the market (as it turned out, there are only a couple of more or less serious publications on this topic in RuNet, and even fewer in Uanet).

Partly wanting to fill the current information vacuum, partly due to the next wave of commercial interest in this democratic and, at first glance, extremely simple idea, we decided to continue the conversation started in the review “PowerLine Networking, or Gigabits from an electrical outlet”, adding it with a story about the cost of effort to achieve stable operation through the power supply network. Readers are offered a detailed overview of PowerLine technology, as well as tests and our impressions of the operation of devices that are already actually available on the domestic market at fairly reasonable prices.

You really don’t take us for fools.
In your project you indicated 70 meters of cable and 10 network sockets.
Do you think our computers are still solar powered?
Did you eat energy? Perhaps you are planning to drill new holes?...
(From a discussion of network costing, 1996)

From this whole rather comical story, when I had to prove for a long time and convincingly financial director a small company that the information cable and sockets really need to be laid and mounted, because the power network is one thing, and the information network is completely different, I remember the final question, symbolizing farewell to the last hope: “So, it’s impossible to use the same wires?” . If you close your eyes to some “non-technical” formulation of the question itself, this person is quite easy to understand. The luxurious renovation of the mansion had just finished, and the need for the organization to operate with a well-established “diskette circulation” system, located in only four rooms on three floors, in a single network was dictated more by considerations of prestige than by pressing need.

Was it possible in those days to answer this question in the affirmative? Back in 1996 no. Wireless networks are expensive and unstable. Both the current technologies and transmission protocols over power networks (X-10, CEBus, LONWorks), as well as many others, which from advertising pages promised to “saturate our home with intelligence” and subsequently sunk into oblivion without a trace, were rather exotic on the domestic market. They were characterized by either a low exchange rate, or poor noise immunity, or the first and second at the same time, and were deterred by the unreasonably high cost of terminal devices.

PowerLine: childhood, adolescence, youth

...and experience, the son of difficult mistakes...

Meanwhile, history has preserved many attempts to use “unsuitable” wires as a physical medium for data exchange. It is easier, of course, to operate with telephone “copper pairs” - their parameters were standardized, and the laying rules were subject to fairly strict requirements, unified in a number of countries. This is probably why the first viable technology for transmission over alternative wires was the technology proposed by Tut Systems (mid-90s). As you know, on its basis, the standard for data transmission over telephone wiring, HomePNA 1.0, was soon adopted. Even though the first version of this standard was not very “advanced”, in a HomePNA 1.0 network with up to 7-10 computers, it was generally possible to get 1 Mbps with a distance between them of about 100-150 m.

Although home network wiring is, for a number of reasons that we'll get to later, an even less fertile environment, the idea of ​​using a single vehicle to power devices and transmit control signals goes back almost to the beginning of the era of electricity. In the patent annals of the 20s of the 20th century, it was possible to discover a proposal based on “... the use of tones of several vocal [sound range. Note author] frequencies for turning on and off devices through the wires through which it is powered.” Moreover, as a control signal setter in the extended patent formula, the enterprising author “stakes out” the use of... a whistle and a microphone with an amplifier.

But it is quite difficult to objectively state who exactly took the next decisive step “into the socket”; the development of technology represented a long chain of tactical research victories and strategic market defeats. Conducted search work were characterized by fragmentation and differed in areas: some companies set themselves the task of getting rid of additional wires when transmitting audio signals; as a result of their work, various “babyphones” and “intercoms” appeared already in the 40s. Others (this already dates back to the end of the 70s) put their efforts into noise-proof control systems via the power supply network, the operation of which did not require high communication speeds. Still others, through various intricacies, tried to “squeeze” the bandwidth occupied by the video signal (it amounts to a few megahertz) into a regular power cable. True, in practice it often turns out that economic efficiency from the use of these solutions, as a rule, turned out to be imaginary.

It became obvious that embodying, albeit sophisticated, but essentially analogue or quasi-digital approaches to the formation, encoding and transmission of information and being bound by the technological limitations existing at that time (such as the high cost of DAC, ADC and other components of the digital processing path signals), commercial versions of “serious” devices cannot be created. This, in the end, cooled the ardor of the explorers, and for a good ten years the idea slowly “cooked in its own juice.” However, you can still find on the market communication devices (intercoms, mini-PBXs) and simple control devices (for example, lighting several lamps in a chandelier) that operate over network wires, mass-produced, and on the Internet you can find descriptions of original projects and various interesting designs: from amateur ones (usually using tones of the audio or ultrasonic frequency range to form a set of commands) to sensors, decoders and command devices for the needs of industrial electronics.

And no matter how childishly primitive these devices may look from the heights of technological development today, it is thanks to a number of conceptual solutions of those years that we can today talk about devices for transmitting information via power supply wires, which have proven in practice that they are capable of ensuring high speed and noise immunity of the process exchange and have sufficient resources to address devices on the network. The latter fact is especially important during mass distribution, as it determines the ability to unambiguously identify to whom the information is directed. For those who consider this requirement not so critical, let us recall an American joke telling how pressing a button on a network remote control remote control coffee maker (apparently working on principles close to the above-mentioned patent!) led to the execution of a command to defrost the refrigerator and turn on the watering of the lawns on the neighbor’s property.

The period of adolescence in the development of technology is usually associated with a number of projects carried out in 1997-2000. experiments on data and voice transmission in pilot projects of leading research laboratories. In addition to little-known companies at that time, such giants of the telecommunications industry as Siemens, Nortel and several communication service providers in Germany and the UK took part in them. And although the plans were truly Napoleonic (Norweb Telecom managed to conclude agreements with a dozen leading energy companies in Eurasia) and promises were distributed generously (1.5 pfennig per minute of work on the Internet), the idea of ​​large-scale use of electrical wiring was once again “out of luck.”

There are many explanations and reasons for this: the high level of spurious radiation from devices, and their cost, comparable to the price of DSL and cable modems, and the design imperfections of terminal devices, and unstable software for them, and severe pressure from large telecommunications companies... All this is true, but, in the author’s opinion, marketing mistakes related to the peculiarities of the perception of decisions by those to whom they were addressed played an important role here. Let us remember that it was during these years that the victorious march of “twisted pair” took place under the slogan “Fast Ethernet to every office.” And the specialists responsible for small office networks, who had suffered with BNC connectors and terminal terminators, were clearly not inclined to experiment with new and, moreover, rather crude technology that did not promise high speeds and inheriting the topology of the boring “coaxial” Ethernet. As for the cautious ordinary burghers participating in the experiments... The expectation is that they will defend a technological solution, even a very promising one, to the detriment of their own current needs and financial interests, as the history of the development of technology repeatedly testifies, is doomed in advance “...show him a copper penny and do with it what you want.”

Even though the first attempts to put the organization of home networks and “distribution” of the Internet on a commercial basis did not lead to the expected revolution in the telematics services market, already in 2001, mass-produced devices with the modest inscription “HomePlug 1.0” proved during operational tests conducted in 500 homes, What effective work via the power supply network is possible in 98% of cases.

Rice. 1. The outlook outlined by analysts is encouraging.

The reliability, survivability and fairly high speed included in the standard, according to analysts, made telephone companies think about how tightly they hold “their piece of the pie,” which served as one of the factors for the further reduction in prices for Internet connection services.

Providing Internet access services is the most attractive, although not the only area of ​​application of technologies for transmitting information over power wires. Today, all known directions within which the development of such systems as the basis for the exchange of information through power networks is seen can be roughly divided into three groups.

Group one. Environment for information exchange between monitoring and control devices of the home automation system

A house full of electrical appliances and hospitably serving its owners appeared in the science fiction novels of Ray Bradbury back in the 60s. And until now, most of us perceive these ideas as popular science fiction, by no means cheap and far from vital. But the original idea is to connect together a controller (control unit), a computer, a printer, a telephone, climate control sensors and various actuators (such as controlled switches, air conditioning, heaters, kitchen appliances, an aquarium and a lawn watering system) there is nothing shameful or supernatural contained. Moreover, its individual elements that are already available for implementation today can and should be considered as the basis for creating a comfortable, autonomous, safe and energy-saving (according to some estimates, up to 20-25% of costs) control system of the future. It can be assumed that as the cost of energy resources and electricity continues to rise, the payback period will decrease. And I would like to believe that in the near future, significant initial investments will cease to be a serious obstacle to their implementation...

It is clear that such a unified environment, including a PC, computer peripherals, and household devices, can only function if there is a local information network, the main requirement for which is a high and guaranteed level of reliability, determined, first of all, by the degree of perfection of the exchange technology used data. It is also obvious that the appearance of interface sockets for connecting USB, FireWire or Ethernet on a kettle, vacuum cleaner or sconce lamp is unlikely to be received with joy by the buyer. Although let’s not promise that there will probably be a manufacturer who will manage not only to integrate all this into his coffee maker, but also to convince the client that he has dreamed about this all his life.

By the way, it is with the advent of new versions of information transfer technologies that the process of rethinking the concept of a home security system is associated, including a wide range of sensors (fire, motion, glass breaking, etc.), monitoring subsystems (including security cameras), fire extinguishing equipment and access control objects. Here, however, emphasis should be placed. For now, we can talk about “secret police” used as auxiliary ones (either additions to existing ones, or autonomous ones), because to connect to a centralized security or fire system An appropriate certificate may be required both for the sensor and, in general, for the technology for transmitting this information. According to a number of preliminary estimates, technical specifications such decisions security systems(primarily in terms of reliability and security of the transmission channel) are comparable or even better than those of existing wireless ones.

Group two. PowerLine Phones & Media

In principle, there are also original devices on the telephone solutions market. So, back in the summer of 2002, the Ascom company from Bern announced that it had begun producing a new series based on a proprietary PLC adapter. The Voice over PowerLine solution offered by the company is based on small, attractive boxes, each of which can connect from one to four voice (or fax) endpoints and organize up to two pairs of telephone conversations simultaneously. The press release emphasizes that the use of new types of products does not worsen the parameters of “computer” exchange in the network on electrical wiring.

Otherwise, telephony solutions are based on standard classic Voice over IP, and PowerLine adapters play the role of banal converters of the Ethernet-to-PowerLine environment, into the network connector of which an IP telephone is connected.

The first experiment in music transfer under the idea of ​​​​combining consumer electronic devices into a single home infrastructure is associated with a demonstration by Motorola, Phoenix Broadband and Sonicblue, when a computer connected to an electrical outlet sent files downloaded from the Internet over the network to a Sonicblue Rio MP3 player.

The main requirements for such systems are to ensure a certain QoS and, in the second case, also to satisfy the growing “appetites” of audio and video streaming applications with high quality. They become stricter if there are several such flows, or if data is transferred in parallel by other types of applications. Practically, when using devices of the HomePlug 1.0 standard, the possibility of transmitting two MPEG-1/2 streams without noticeable delays while maintaining network activity (a certain average standard “streaming turnover”) between five or six other subscribers was proven. A significant event was the practical demonstration at the Consumer Electronics Show held in Las Vegas in early 2003 of the first transmission at 30 fps of high-quality video over the PowerLine network deployed at the stand. The show was held by ViXS Systems (developer of chips and video software) and Cogency Semiconductor (manufacturer of the PiranhaT chipset). By the way, it is reported that the experiment was duplicated by broadcasting via a WLAN channel, and the difference between the first and second transmission methods could not be detected.

Group three. PowerLine Networking and PowerLine Internet

The trend of increasing the number of computers in the home continues to gain momentum, which requires the emergence of cheap and convenient means for combining computers and peripheral devices into a single network when laying new wires is unacceptable or impractical (Fig. 2).

Rice. 2. Structure of the PowerLine home network. Connecting to the intranet/Internet

However, by discussing only one case - connecting several devices within one apartment or private house - the possibilities of using PowerLine are not limited.

The second aspect of using network-over-power technology is to solve the problem of “last mile” and “last feet” when connecting to the Network. Moreover, in 1999, such a solution to the problem was considered so economically correct that a project was “promoted” with the sonorous abbreviation PALAS PowerLine for Alternative Local AccessS, designed in every possible way to promote the introduction of technology into the European market. The calculation of its participants was based on the fact that power supply networks cover up to 95% of human-inhabited areas. Cells of such infrastructure are quite regular, and, according to preliminary estimates, the number of potential users, to cover which there is no need to create a new cable infrastructure, exceeds the number of telephone subscribers by 1.5–5 times (depending on the level of telephony in the region). Experts reasonably believed that where telephone communications are underdeveloped, the demand for connecting to the Internet via the electrical network will be an order of magnitude higher. True, as for PALAS itself, judging by the state of the site palas.regiocom.net, the work of its members is not particularly active.

The structure of such information education may be similar to that shown in Fig. 2. The designed maximum bandwidth per subscriber is usually reduced to 300–500 kbps. At the same time, however, the requirements for the minimum level of information security(mechanisms for user authentication and encryption of data streams) after all, the topology of the formed network is similar to the topology of coaxial Ethernet and allows “everyone to listen to everyone.”

For those who find PowerLine’s “reception” capabilities insufficient, we can offer to use already proven solutions for asymmetric access to information. For example, from a satellite the user receives incoming traffic at speeds of up to MBps, and sends small outgoing traffic via terrestrial communication lines. This solution to the “last mile” problem easily fits into the above structure and is primarily aimed at small companies and discerning private users.

However, here we will have to make a small digression, recalling the differences between foreign power supply systems and the domestic one. If in most countries of the world it is customary to connect two phases and a protective “zero”, then almost all apartments of Ukrainian energy consumers are content with connecting to one of the three phases of the 380 V network and “zero”, i.e. if we consider the task of building a single network based on an apartment building (and the maximum range of HomePlug devices allows this), then in order to unite all users into a “common bus” between “phases” it will be necessary to enable the corresponding bridges. Without going into the details of the circuitry, this is enough simple device, we note that the task of creating infrastructure may go beyond the simple installation of ready-made solutions, tested and certified in the West. Although, with a large number of clients, it may be advisable to combine three groups (subnets) into a single network using an appropriate switch immediately before introducing an external channel into the house.

Concluding this small analysis, let us once again stipulate that the attempt to distinguish between services is more than conditional in the development of modern network technologies The next most important trend after increasing speed is the desire to combine in a single network stream different kinds traffic (data, telephony, video). Another thing is that the required bandwidth for all the desired services at the same time (and, as it turned out, for PowerLine devices it is even less than 10 Mbps) may not be enough (Fig. 3).

Rice. 3. The trend towards combining all groups of devices. Is there enough bandwidth?

And finally, those who intend to organize the provision of Internet access services will have to return to the issue of developing a software package for remote administration and monitoring with advanced functions due to the specifics of this technology. Such a kit, in addition to the standard network capabilities for this case, should allow:

• detect all devices on the network and determine their type ( Ethernet adapters, USB or PCI card) and the MAC address assigned by the manufacturer, as well as provide the administrator with the ability to determine and assign the device’s IP address;
• conduct constant monitoring of the network and create graphs of the congestion of a particular area, as well as collect traffic statistics for each of the protocols used, quickly monitor and check the quality of the connection with each device on the network (at the physical connection level);
• remotely manage clients’ access rights to the service (connect/disconnect a user), change the password to create a user network with your own security settings. It would be useful to provide the operator with the ability to assign which of the specific devices (if one client has several of them) to allow access to the service. Thus, it will be possible, for example, to block the installation by the user of any PowerLine adapter purchased by him independently without approval from the service provider.

Looking ahead, we note that today, of all the software packages reviewed, the Open PowerLine Management software package from Corinex is the closest to these requirements in terms of functionality. It includes the PowerNet Setup Tool, which allows you to find all the MAC addresses of available PowerNet devices. However, in practice it turned out that for it to work, at least one “native” device must be present on the network.

We'll leave it at that for now, leaving economists to conduct a more in-depth analysis. It is obvious that the potential inherent in PowerLine is enormous, and as of today, the use of technology can become a business subject, in particular, for energy supply companies. An example is the Mosenergo program in Zelenograd, the former “silicon capital” of Russia. At the first stage, it is expected to resolve pressing problems associated with accounting for electricity consumption and managing the energy supply system. Next year it is planned to provide services for Internet access, IP telephony, teleconferencing and others.

Technologies for transmitting control signals and information over network wiring

PowerLine definition and classification

PowerLine, Powerline Communications (PLC) family of communication technologies that are based on the use of the existing power supply network (120 V, 220 V, etc.) as a physical medium for information dissemination.

Both existing research areas within the framework of these technologies and devices already implemented “in hardware” can be differentiated by exchange speed.

1. Low-speed exchange (Low Baud rate, sometimes below 0.05 Kbps) with transmission ranges of up to tens of kilometers. Similar PLC systems are already used in the energy sector on high-voltage main systems for transmitting service telemetry information.
2. Exchange at an average transmission rate (Medium Baud rate, usually in the range from 0.05 to 50 Kbps) over average distances not exceeding several kilometers. Such PLC systems allow the implementation of simple control applications and are focused on existing network power infrastructures (home automation, lighting control systems, organization of automatic measurements, monitoring via the Internet, etc.). Information is transmitted in the frequency band 50-535 kHz.
3. High-speed exchange (High Baud rate, from 100 Kbps). The main purpose is “computer” local data exchange. Classic tasks for such systems usually include the task of combining existing printers, scanners and other devices into shared resources, as well as organizing a home or SOHO computer network. It would be fair to include in this class the solution to the entire range of multimedia problems. Due to a number of conflicting requirements, devices are forced to occupy a fairly wide frequency band (in the range from 1.7 to 30 MHz) and provide operation at a distance of up to several hundred meters. Homeplug PowerLine devices fall into this category.

Problems related to the transmission medium, or
Is it really that complicated?

Actually, if we delve deeper into the technical problems, we can try to explain why the cost of a PowerLine adapter cannot be compared with an Ethernet card. Do not forget that the latter is designed to be used in combination with a specially designed transmission medium, and this is what allows it to be simple, accessible and cheap. But once you start transmitting over “non-specialized” wires, the design becomes complex and expensive: it is forced to compensate with its complexity and high cost for working with surrogate network cables.

Let's take a closer look. In the future, we will be interested in a frequency band of several tens of megahertz; its minimum value is determined by the information bandwidth that needs to be provided, in our case up to tens of Mbps. So, in a network cable with increasing frequency (as, indeed, in any other feeder), the value of linear attenuation increases (Fig. 4).

Rice. 4. The power cable itself is not the best environment for propagation of high-frequency signals

In practice, this means that, wanting to receive and process the entire frequency spectrum of the original signal at the other end of the cable, we will have to transmit its high-frequency components tens of times higher in level than in the low-frequency part. There are quite strict restrictions on both the range of frequencies that signals in a cable can occupy and their maximum levels, which forces the use of special techniques to reduce the spectral power density of signals and at the same time use ingenious methods for economical representation (coding) of the original digital signals .

The next problem inherent in apartment network wiring is the reflections that arise in it from inhomogeneities in its structure. Each splice of wires, group of contacts, parallel connection and branch of wires leads to multiple interference of direct/delayed signals and to frequency-selective attenuation. By turning on the light, turning something on and off from the network, using extension cords, we are constantly changing the parameters of this structure, not only for ourselves, but also, to some extent, for our neighbor, powered from the same “phase”. This leads to a fairly well-known effect in wireless radio systems and multimode fiber optic communication lines called intersymbol interference (ISI). There it is caused by multipath propagation of radio waves (i.e., the simultaneous arrival at the receiver of several signals shifted by a certain amount proportional to the difference in the distances traveled by each of them). As a result, a short pulse is “blurred” and turns into a wider one or even into a sequence of several, i.e. the transmitter emitted one pulse corresponding to a symbol (or several symbols in a row corresponding to an information group), but a whole series is detected at the receiver, which leads to to their incorrect interpretation and, as a consequence, to errors in the transmission session and limitation of the maximum channel capacity.

But the total number of different terminal devices that actively influence the parameters of the power network, even in small house cannot be counted. Moreover, many of household appliances(vacuum cleaners, mixers, PCs with cheap power supplies, fluorescent lamps etc.) not only make “noisy”, but are also capable of generating, at the moment of startup, long-lasting series of pulses with amplitudes that are an order of magnitude higher than what we would expect in a 220 V outlet. To this “electrical mess” all that remains is to add a few burnt contacts on the panel and the legendary “Uncle Vanya” with welding." To complete the picture, it is also recommended to remember that network wires not only emit, but also do a fairly good job of receiving radio waves (the band we selected includes radio stations of at least three broadcast and four amateur wavelengths) in order to understand the tangle of problems that device developers are dealing with PowerLine have been fighting for decades.

The nut is hard, but still...

Work continues to improve software products. In a joint statement by Intellon and Corinex, production was promised by May 2003 software, based on the open standard MIB (Management Information Base). Its use will make the installation process more “transparent” and expand the capabilities of local and remote network administration of devices based on Intellon chips (HomePlug 1.0.1 specification). Note that since the HomePlug 1.0.1 standard has so far been implemented “in hardware” only in the development of the “pocket” company of the Intellon alliance, at this point in time we can equate its chipsets with the standard itself. In the meantime, the Corinex website contains the contents of an installation CD containing drivers, PowerNet Setup Tool software and an SNMP agent for PowerNet, which work only with their “branded” devices.

conclusions

Let's summarize all of the above. The entry into the market of PowerLine devices of the HomePlug 1.0 standard from different manufacturers who quite easily find a “common language” suggests that the technology has finally been “cleansed” of serious hereditary compatibility problems and has moved from the category of exotic to the level of commercial use. One can only be surprised that such a logical invention in the “need for inventions is cunning” style did not appear in the post-Soviet space. Although, on the other hand, such a solution, due to the “obstinacy” of the transmission medium, requires implementation in hardware quite complex principles and assumes that the developer has all the production elements of the technological cycle, allowing him to bring the idea to the stage of commercial operation.

Although the stated maximum theoretical throughput of PowerLine networks is 14 Mbps, the actual average data transfer speed turned out to be 5-6 Mbps. These indicators are comparable to the characteristics of HomePNA and wireless networks (WLAN) according to IEEE 802.11b and HomeRF 2.0. The technology is easier to implement than telephone networks, because while a telephone socket is not found in every room, power sockets are everywhere, and even more so next to a computer or printer. There are no “dead zones” typical for wireless solutions (when it is impossible to receive a signal at certain points in the room), and its organization can be cheaper than installing wired Ethernet from scratch. Although the current cost of PowerLine devices per user is comparable or even higher than the price of a WLAN kit (Wi-Fi, excluding the cost of a license), there is every chance that as more companies start producing devices, it will gradually decrease.

For each of the main parameters, HomePlug technology has a worthy competitor. But despite a number of promises to “cheaply connect everyone to the Internet” using other technologies, there is no clear universal solution that combines acceptable quality and simplicity with minimal initial and proportionate subsequent investments for infrastructure on the scale of, for example, an average city home. In contrast to those already mastered, transmission technology via power network wires is characterized by a relatively low level of initial investment due to savings on investments in creating a physical transmission medium. PowerLine networks scale well, i.e. they provide stable operation when connecting new clients, and sufficient power is retained for most practical applications operating speed, proportionally decreasing with increasing distance (up to 200-300 m).

A number of experiments we have conducted show that the high resistance to interference and non-criticality of the transmission medium, embedded in the HomePlug standards, allow us to consider ready-made devices as a kind of semi-finished product for developing our own home and industrial wired solutions.

In the meantime, we want to believe that the devices announced at CeBIT (combined WLAN/PowerLine access points, routers and ISDN/DSL-to-PowerLine modems, multimedia players, video cameras with built-in support for this technology, new Voice over PowerLine, as well as integration kits) to a home network of computers, Web tablets and MP3 players) are already on their way to our customers. Even if these devices are not so widespread yet, this, as far as one can judge from the results of trial operation, is just a matter of time...

This article will discuss methods for transmitting data over power wires of devices. Particular attention is paid to the problems that need to be solved by the developer of such communication devices. Examples are given of the implementation of the receiving and transmitting parts for communication lines via power wires direct current, as well as the implementation of a communication channel via AC power wires of 220 Volts with a frequency of 50 Hertz. Typical algorithms for the operation of a control microcontroller are described.

A little history

The idea of ​​transmitting control signals over power wires is not new. Back in the 30s of the last century, bold experiments were carried out to transmit such signals through the wires of the city's power network. The results obtained were not very impressive, but we should not forget that in those days lamp technology reigned and the element base was not so diverse. To all the problems of a technical nature were added organizational ones: there was no uniform standard- each developer did everything for himself: different frequencies and modulations were used. All this hindered the development of this communications industry.

Operating principle of transmitting and receiving devices

The operating principle of such devices is to transmit high-frequency signals through DC or AC power wires. In AC power lines, signals are most often transmitted at the moment the AC current crosses zero, i.e., when the power voltage is absent or minimal ( Figure 1a). The fact is that the level of interference at this moment is minimal ( Figure 1b). In this case, the signal useful to us is transmitted as if between a series of interference ( Fig 1c).

Rice. 1 (a, b, c). Transmission of a high-frequency signal over an alternating current network

A transformer is most often used to transfer a high-frequency signal to a power network. The receiving part usually consists of a communication transformer and a circuit on which the necessary high-frequency signals are isolated ( Rice. 2).

Rice. 2. Method of transferring high-frequency signals to an alternating current network

In DC power circuits, a similar method of transmitting high-frequency signals is used, but the principle of generating such a signal is different: a powerful switch (transistor) with its transition briefly bypasses the network. There is a slight decrease in network voltage ( Rice. 3).

Rice.3 . Method for generating high-frequency signals in DC networks

A sensitive detector is installed on the receiving side, which detects these voltage dips in the line. Next, these signals are supplied to the input of an amplifier with an AGC function, after which the received signals are transmitted to a logic block, which can be implemented either on small-scale integration microcircuits or on a universal microcontroller or a specialized microcircuit that includes all of the above components. Recently, microcontrollers are increasingly used for such tasks due to their low price and great capabilities. Moreover, the use of programmable devices allows you to change the purpose of such devices by loading into them new program- this is much simpler and cheaper than making a new electronic device with a dozen microcircuits... ( Rice. 4)

Rice. 4. Block diagram of a modern PLC modem

Advantages and disadvantages of this type of communication

The advantage of this type of communication is the sharing of an existing wired power line. That is, there is no need to install a communication line, and there is an outlet in almost any room.

The disadvantages include both the technical complexity of the device and the low speed when transmitting data over distances greater than 100-300 meters.

Also, do not forget that this communication channel can only be organized between those devices that are connected to the same phase of the network and only within one transformer substation- high-frequency signals cannot pass through the transformer windings of an electrical substation.

Note .

In principle, the last limitation is partially removed by the use of passive or active repeaters of high-frequency signals. They are used both for transmitting signals to another phase, and for transmitting signals to the line of another transformer.

Technical difficulties of implementing a communication channel

Organizing a reliable communication channel over a power network is a non-trivial task. The fact is that network parameters are not constant, they change depending on the time of day: the number of devices connected to the network, their type and power change. Another negative feature of the electrical networks of the countries of the former USSR is “hegemony” - powerful transformer substations that power entire neighborhoods! Accordingly, hundreds of subscribers are connected to one phase of the transformer, each of them has a a large number of all kinds of devices. These are both devices with transformer power supplies and devices with switching power supplies. The latter are often implemented with violations in terms of electromagnetic radiation - interference, which creates a very high level of interference in the power network of the building and the city in particular.

Note .

In many countries, compact batteries are used to power buildings. transformer devices. One such transformer powers from 3 to 7 apartments or houses. Consequently, the quality of electricity supplied to subscribers is significantly higher than in our electrical networks. Also resistance between phase wire and neutral higher. All these factors allow us to have Better conditions for transmitting data within an apartment or building than we have in our conditions.

A large number of devices connected to the network leads to low resistance between the phase wire and zero; it can be 1-3 ohms, and sometimes even less. Agree that it is very difficult to “swing” such a low-resistance load. In addition, do not forget that the networks are very large in area, therefore, they have large capacitance and inductance. All these factors determine the very principle of constructing such a communication channel: a powerful output of the transmitter and high sensitivity of the receiver. This is why high frequency signals are used: the network has more resistance for high frequencies.

No less a problem is the poor condition of power networks, both in general and inside buildings. The latter are often carried out with violations, and even the minimum requirement is violated: the main line is made with a thicker wire than the outgoing supply lines to the rooms. Electricians know such a parameter as “phase-zero loop resistance”. Its meaning comes down to a simple relationship: the closer to the electrical substation, the thicker the wires should be, i.e., the cross-section of the conductors should be larger.

If the cross-section of the wires is chosen incorrectly, the laying of the main line is done “as it happens,” then the line resistance dampens high-frequency signals. The situation can be corrected either by improving the sensitivity of the receiver or by increasing the transmitter power. Both the first and second are problematic. Firstly, there is interference in the communication line, so increasing the sensitivity of the receiver to the level of interference will not increase the reliability of signal reception. Increasing the transmitter power may interfere with other devices, so it is also not a panacea.

Common standards. Standard X10

The most famous of the standards for transmitting commands over the power network is X10. This standard was developed a long time ago, in 1975 by the Scottish company Pico Electronics. Data is transmitted using a burst of pulses with a frequency of 120 kHz and a duration of 1 ms. They are synchronized with the moment the alternating current passes through zero. One bit of information is transmitted per zero crossing. The receiver waits for such a signal for 200 µs. The presence of a flash pulse in the window means a logical “one”, its absence means a logical “zero”. The bits are transmitted twice: the first time in direct form, the second time inverted. Typically, modules are implemented as separate devices, but now they are increasingly implemented not on the basis of different components, but using a microcontroller. This reduces the size of the receiver, allowing smart hardware to be built into even a light bulb socket or doorbell.

As mentioned earlier, a high-frequency signal cannot propagate beyond the transformer substation and phase. Therefore, to obtain communication in another phase, so-called active repeaters are used. But it must be taken into account that the receiver listens to the signal only at certain times. Therefore, they use either “smart” receivers with changed parameters

This communication standard has both pros and cons. Firstly, he developed it a long time ago, there were no microcontrollers then, and all circuitry was analog, using numerous components. Therefore, the communication protocol is very low-speed: no more than one bit is transmitted in one network period. The fact is that the bit is transmitted twice: in the first half-cycle it is transmitted in direct form, and in the second half-cycle - inversely. Secondly, some commands are sent in groups. This further increases the communication time.

Another significant disadvantage of this protocol is the lack of confirmation of command receipt by the device. That is, having sent a command, we cannot be sure of its guaranteed delivery to the recipient. This also does not promote the spread of this standard.

Own experience. Let's reinvent the wheel.

Having tested in real conditions numerous ready-made devices that allow transmitting commands over a power network, I came to a disappointing conclusion: at home, with a limited budget, without specialized devices and (what is there to hide?) knowledge, it will not be possible to invent something ingenious . But nothing and nothing prevents you from making a nice craft for yourself, under your specific conditions. This also means the scope of application of such a product, the distances over which commands must be transmitted, as well as the functionality of such a device.

Let's complete some formalities in the form of some kind of terms of reference for our project.

1. the device must transmit data via power network wires;
2. data must be transmitted during current “pauses,” i.e., when the network voltage is minimal;
3. the reliability of the communication channel is ensured both in hardware (optimal signal level at the receiving point) and in software (data is transmitted with a checksum to detect damage to the received data, commands are transmitted several times, the fact that the receiving device has received the command is confirmed by sending a corresponding signal back to the host device);
4. let's simplify to required level both data exchange protocols between devices on the network and the type of modulation. Let's assume that one bit of data is transmitted for 1 millisecond. A unit will be transmitted in the form of a burst of pulses of this duration, and a zero will be transmitted in its absence;
5. on the network, all devices listen to signals, but only the device to which such a command is addressed executes the received command. That is, each device has its own individual address - number.

The circuitry itself of the executive part of such devices may be different. We are interested in the circuit of the receiving and transmitting parts.

On Fig 05 shows a diagram of a real device transmitting commands over a power network. The executive part of the device controls the brightness of the lamp, i.e., it is a dimmer.

Let's take a closer look at the diagram. Transformer T1 and diode bridge D1-D4 provide power to the device. Node R8\R11, diode D6 and transistor Q1 provide formatting of the signal indicating the minimum voltage in the power network (frequency 100 Hz). Buttons S1-S3 are used to locally control the operation of the dimmer: they change the brightness of the lamp, allow you to save this parameter as default, as well as the rise and fall time of the lamp. The LED displays the dimmer operating modes and the fact that signals are being received. The remaining LEDs display the brightness of the lamp and the time of brightness change.

Resistors R11 and R12 form a voltage divider and are used to set the “sensitivity” of the receiving part of the device. By changing the resistance ratios of these resistors, you can influence the device’s response to both interference and the useful signal.

The T2 communication transformer is used for galvanic isolation of the receiving and transmitting parts of the device, and also transmits high-frequency signals to the building’s power network.

The transmitting part is made of transistor Q2 and one of the windings of transformer T2. Pay attention to the zener diode D5 - it is this that protects the transistor junction from breakdown during short-term high-voltage interference in the network.

The receiving part is somewhat more complicated: one of the windings of the transformer T2, together with the parallel oscillatory circuit L1\C2, form a complex circuit of the receiving path. Diodes D8 and D9 protect the microcontroller input from the voltage limit. Thanks to these diodes, the voltage cannot exceed the value of the supply voltage (in our case 5 Volts) and cannot become negative below minus 0.3-0.5 Volts.

The process of receiving signals is carried out in the following way. Polling buttons and working with the display do not have any special features. Therefore, I will not describe their work.

The receiving subroutine waits for a current zero crossing signal. Upon the occurrence of this event, the analog comparator polling procedure is launched, which lasts about 250 microseconds. If no signals were received, then the subroutine starts its work from the very beginning.

When any signal is received (the comparator has issued a logical one at its output), the procedure for analyzing the received signal is launched: for a certain time, the comparator is polled for the presence of a long signal. If the received signal has the required duration, then the received signal is considered reliable. After this, the admission procedure starts required quantity bit of data transmitted by the remote device.

Having received all the data, it is analyzed to see if it matches the checksum accepted in the same parcel. If the data is received reliably, then the command is recognized as valid and executed. Otherwise, the received data is ignored and the program is executed again.

The process of transmitting signals to the network is also carried out entirely by the microcontroller. If it is necessary to transfer data, the subroutine waits for the starting condition: receiving a current zero crossing signal. Having received this signal, a pause of 80-100 microseconds is maintained, after which a packet of pulses of the required frequency and duration is transmitted to the power network. High-frequency signals pass through a small capacitance with virtually no loss high voltage capacitor C1 to the network. Bursts of the required frequency are generated using a hardware PWM generator available in this microcontroller. As experiments have shown, the most optimal signal transmission frequency lies in the range of 90-120 kHz. These frequencies are allowed for use without the need for registration with the relevant supervisory authorities in both Russia and Europe. ( StandardCENELEC)

And now the answer to the most frequently asked question: What is the communication range between such devices? The answer is simple:

The communication range is influenced by many factors: the quality of power lines, the presence of “twists” and mounting boxes, the type of load and its power...

From practice: in a small town, on a power line supplying 30-50 private houses, in the morning and during the day (when less electrical appliances are used) the communication range is significantly higher than in big city with hundreds of apartments in one phase.

I will answer the second common question: how to increase communication range? To do this, you can increase the power of the signal transmitted to the power network, as well as improve the receiving part of the device.

The power amplifier can be made using the common TDA2030 or TDA2003 chip (although the parameters declared by the manufacturer are different, they work well)

The receiving part is more difficult to modify:

1. add an input amplifier and AGC;
2. add narrowband filters at the input of the device. The simplest solution is this: a serial circuit tuned to the required frequency.

This material is prohibited from copying and distribution, either in whole or in part, without permission.

21-11-2013

Julia Truchsess

Electronic Design

The circuit solves the problem of information exchange via a cable in which there are no free wires left. An amplitude-shift keyed carrier signal can be transmitted over low-voltage power lines.

Sometimes it becomes necessary to organize data exchange when there are no more unused conductors left in the device cable for a dedicated communication line. Typically, this problem is solved using a high-frequency carrier modulated by data and transmitted over power lines, in particular, along the wires of home electrical wiring.

Searches on the Internet showed that, despite the relevance of this problem for many developers, no one offers simple, cheap and reliable solutions for low-voltage systems. Below is the result of an attempt to fill this gap. Please note that without special circuit safety precautions, this circuit is not suitable for high voltage applications.

The device, which requires only a handful of discrete components and a couple of chips, can reliably transmit and receive data at speeds of up to 32 kbps on a carrier frequency of 2.6 MHz. This speed could likely be increased many times over by using a higher carrier frequency and changing component ratings accordingly. The circuit can operate on a cable with a capacitance of up to 10 nF and has a low level of electromagnetic radiation. It transmits data in a standard serial asynchronous format compatible with UART, but nothing prevents developers from using Manchester encoding or other protocols.

For simplicity, carrier amplitude manipulation is used and no circuit solutions are provided to suppress intrinsic noise, other than a good signal-to-noise ratio. If desired, developers can implement software error detection and correction.

A PIC microcontroller with a set of peripherals is ideal for our circuit. In particular, its PWM module or programmable timer will be used to generate square-wave carrier signal pulses, as well as a high-speed comparator with rail-to-rail inputs (Figure 1). Of course, if you have the appropriate peripheral devices, you can use any other microcontroller.

The diagram shows two transceivers. Transceiver 1 (left) is the "remote" node receiving power from the "base" Transceiver 2 (right). Inductors L1 and L2 isolate the high-frequency carrier from the low-impedance power rail.

Several nodes can be connected into a multipoint bus if each node is separated from the power line by decoupling inductance. Small surface-mount inductors can be used, but their operating current must provide power to the load with some margin.

The transmitting part of the transceiver is made on a single-channel three-stable U2 bus driver of the TinyLogic () family. The driver outputs are connected to the bus through elements R1 and C1. Resistor R1 provides some filtering to reduce the level of electromagnetic radiation generated by the steep edges of the rectangular carrier.

The receiver connection point is formed by elements C2, D2 and D3, followed by two peak detectors. The first detector, with a time constant equal to approximately one-third the duration of the information bit, demodulates the carrier to restore data synchronization. The second, with a time constant approximately 50 times the duration of the data bit, adaptively restores the carrier level. Resistors R3 and R5 divide this level to approximately two-thirds the carrier amplitude.

The outputs of both detectors are connected to the inputs of the internal analog comparator of the microcontroller, which finally generates rectangular data signals, which are then sent to the UART through an external circuit. Resistor R4 slightly biases the non-inverting input of the comparator upward to provide a predictable log level in the absence of exchange. 1".

It should be noted that the input and output of the transceiver are always connected together, so care must be taken that the program ignores signals received from its own transmitter.

In Figure 2, the yellow waveform shows the raw digital data sent by the remote transceiver to the transmit UART port. Blue shows the result of carrier modulation as seen on the power rail. Pink color indicates the demodulated and reconstructed signal coming from the comparator output to the RXD UART input.

Figure 3 illustrates the details of the demodulation and data recovery process. The input amplitude-keyed signal (blue), after processing by two detectors, is fed to the inverting and non-inverting inputs of the comparator (yellow and green, respectively). The data recovered from the comparator output is shown in pink.

Julia Truchsess made successful career, creating a range of electronic toys including MicroJammers, Rhythm Rods and Singing Bouncy Baby, many of which sold millions of copies. In the late 1990s, Julia came up with the idea of ​​digital photo frames, the production of which was soon organized under the Digi-Frame brand. After the debut of Digi-Frame, many began to produce similar products large companies, but according to reviewers, the Digi-Frame was "the Rolls-Royce of frames."

Julia runs Pragmatic Designs (www.pragmaticdesigns.com), founded in 1986.

To comment on materials from the site and gain full access to our forum, you need

» Interfaces
» Computers and peripherals
» Laser
" Medicine
» Monitors
" Music
» For beginners
» Open MK platforms
» Advanced technologies
" Nutrition
» Application of microcontrollers
» Radio
" Radio controlled models
» Retro
» Robotics
» CAD and software
» Lighting technology
» Networks
» Power electronics
» Solar energy
" Cellular
» Satellite equipment
" A television
" Telephone
» Theory
» Directions for use
» Digital
» Arduino

Search for: "Multi-command control of loads over two wires"
Added words from the dictionary: " wire "

Radio designer, November 2015 Maksimov A.N. In the article Multi-command control over the power grid (RK 06-2014, pp. 35-38), the author proposed a simple circuit consisting of...
.. N. Multi-command control over the electrical network. zh.Radioconstructor, No. 6, 2014, pp. 35-38. Rybin L.N. Remote control system for sixteen objects. and. Radioconstructor, No. 6, 2014, pp. 21-23.
.. the transistor is almost open (resistance R3 is chosen such that the voltage at its collector does not exceed 2-3 V). And its load is the generator on VT1 and VT2. If a low-frequency signal is applied to the base VT3 through capacitor C5, then...
.. pressed keyboard button. To convert the binary code at output D1 into decimal code, a decoder is used on two multiplexers D2 and D3 of the K561KP2 type. Each chip has eight channels connected to one common point Y...
.. determined by the L2-C2 circuit tuned to a frequency of about 135 kHz. This signal is fed through capacitor C1 to the phase wire (necessarily to the phase wire). In this case, the neutral wire of the network is connected to the common wire of the transmitter. Current on...

19-09-2016

The load requires additional wires, as well as installing a resistive sensor near the load, which is extremely difficult when the load is inaccessible for intervention. Another method is to minimize the voltage drop by...
.. single-wire compensation method. If the remote load circuit does not share a ground with the regulator, two wires will be required: one to the load and one to provide the ground bus return current path. Current sensor amplifier...
.. gaskets, which sometimes may not exist and, in addition, leads to an increase in the cost of the system. An alternative to additional wires is to compensate for the voltage drop in the line directly at the regulator using a special...

Design Note 529 Introduction A common problem in power distribution systems is loss of regulation due to the cable/ wire voltage drop between the regulator and the load. Any increase in wire resistance, cable length or load current ...

20-10-2015

.. (PPTF) and rear (ZPTF) fog lights. Based on the presence of one standard PTF switch in the car, a control circuit for one non-fixed button of two relay switching circuits (PPTF and ZPTF) is required. The PPTF circuit is turned on constantly...
.. on the diagram), and naturally, power supply - pins 7 and 14 of both MSs. Due to the presence of a limiting resistor in the power supply circuit, the load on the outputs should not exceed approximately 1 mA. (or you need to reduce the value of this resistor accordingly, ...
.. the same thing, only the compression is different, but it’s still strange - is this how it should be or what? :rolleyes: I go to the edit - there are two, but in the message there is one... :confused: Ah, now I understand - they are simply displayed differently - one is like a picture, the other...
.. one non-locking button for two relay switching circuits (PPTF and ZPTF). The PPTF circuit is turned on by a constant short circuit to the common wire of the corresponding relay contact. The ZPTF circuit is turned on by a short-term short circuit to the common wire of the control...

04-04-2008

Like a 17-year-old girl in a pioneer camp, IMHO!!! I agree with hrpankov, it is much more efficient to use a full bridge. If the control is assembled using half-bridge IR drivers, then the power section circuit, not counting the necessary current protections, ...
.. with Donetsk. He probably already digested all this a long time ago. ;) http://www..php?t=18305 hrpankov, loading with a resistor is not at all equivalent to loading with a capacitor, which at the beginning of the charge is for...
.. skew so that one of the blocks does not turn off? Those. Was the total current consumption distributed between the two blocks in half? Can it help in my case if I install a diode bridge at the output of each block (as a protective...
.. - made on U-shaped ferrites, and the coils, the entire frame - everything was turned and milled for a certain number. turns of wire. Those. At first I got a trance on - and now I’m thinking about how to power it. There is always an option - linear...

05-02-2016

The 82 V bias and +500 V screen voltage are obtained from transformer T1. The +24 V control voltage is removed from transformer T2. Diode bridges VD13 VD17 and smoothing capacitors C8 C12 are used to obtain high...
.. according to a circuit with sequential connection of rectifiers, which is done using switches SA4, SA7 (switch without load!). In addition, one of the secondary windings of the T3 transformer is divided into two separate identical windings, ...
..with its help, lines L2-1, L2-2 are tuned into resonance at the desired frequency. Differential capacitors have two isolated stators, the terminals of which are connected to the resonant line, and a common rotor, which is connected to the housing. ...
.. the required voltages are supplied via a 20-wire cable from the power supply to the PA. For incandescent circuits, the cable cores are soldered in parallel. An additional polyvinyl chloride cambric is placed on the high voltage wire over the main insulation...

10-02-2007

The limit switch is triggered and the engine stops - based on this, think, all this is very simple, and you are almost ready to put a controller on the control. And in terms of time, apparently, it will be bad, because... The speed of rotation of the engine depends greatly on...
.. voltage in the motor, or will it be necessary to reduce accordingly permissible load per motor (more precisely, to maintain the same load, you will have to make a larger and more expensive motor than a regular single-winding one). In all the ones I've met...
.. three-position switch without fixing (extend-neutral-hide). Antennas of the first type need three wires - two for power and one more for the control signal, while antennas of the second type only need two wires directly from...
.. you need more than one block, open it and copy it. The antenna operation algorithm is as follows. Power supply and one signal from the radio (blue wire). If it has +12V, the antenna extends. +12 disappears - the antenna moves in. Relay reverse. Current limiter...

13-09-2006

The problem is this: I want to install it on a non-original car dashboard, but the catch is that the tachometer receives exactly 2 times more pulses from the control unit than are needed for correct readings. That is, the tachometer...
.. powered it from the 7805 stabilizer (to ground through 200 Ohms - girth +1 volt, total Upit = 6 volts). I didn’t bother buffering, the load there is negligible. I encountered the same problem, the tachometer shows 2 times more than expected, I collected...
.. as close to the conclusions as possible) I also wanted to add that the zener diode at the input does not suppress short-term interference. It is better to replace it with two diodes connected in series, the middle point is connected to the input, minus chains to plus power, plus chains...
.. the necessary conclusions with pieces of copper wire. For example, we connect pins 3, 4, 5, 6, 7, 8 and 10 with one wire (this is a common wire, i.e. minus power supply - by the way, the MS can be fixed to a sufficient piece of a common conductor by soldering it to it...

17-01-2007

14-03-2007

Therefore, I would be very grateful for specifics (which relays should be installed, markings). I know there are car ones, the control current is 0.2 A, the voltage is 12 V, but the output signal will be 3 V. For all other relays, my knowledge is...
.. Maybe it’s better to get up to transistors right away? I would also try to put them on the output, if possible, if the load is permissible. Glass does not interfere with IR rays, as a rule, even darkened ones. SD and FD can be taken from any of...
.. DU. sirak! Maybe you can tell me something? There is a set of m/cx TX2/RX-2, used in Chinese toys. Five-team. Just like two fingers... can you help me with anything? if it's diagrams, then it was already in this thread...
.. diode or resistor - in the case of a diode, the reverse polarity of its connection must be observed), the contact group - into the break of the load power supply wire, depending on the desired operating algorithm (on or off). Basically...

18-06-2007

Both will be blocked. Apparently in this case it is necessary to make the entire system asymmetrical, with explicit priority to one of the control signals - then only one new relay with the ability to switch (block another circuit) will be required. ...
.. sensor Then you will have to replace the original relays with others, specially selected for the same operation and load parameters. Moreover, when connecting both relays and blocking the other without priority, it is possible that both...
.. with water flows - let's say there is some initial water reservoir (analogous to a substation), from which two channels go to two intermediate reservoirs (houses), where some kind of water consumption occurs and from these same two reservoirs go...
.. can they agree on something:confused:? The scheme, both through pipes and wires, will greatly depend on the degree of agreement. And for accurate calculations you can’t do without separate meters (either for water or electricity): o.

04-07-2007

Pages: