What is a data dictionary? - Dataconomy - Dictionary

Let’s start by answering the first thing that comes to mind: What is a data dictionary? A data dictionary, also known as a data definition matrix, contains comprehensive data about the company’s data, such as the definition of data elements, their meanings, and allowable values.

The dictionary, in essence, is a tool that allows you to convey business stakeholder needs in a way that allows your technical team to build a relational database or data structure faster. It aids in the prevention of project disasters, such as requiring information in a field for which a business stakeholder can’t reasonably be asked or expecting the wrong type of information in a field.

Table of Contents

Data dictionary definition

It is a compendium of terms, definitions, and attributes that apply to data elements in a database, information system, or study portion. It explains the denotation and connotation of data elements in the context of a project and offers recommendations on how they should be interpreted.

A data dictionary also includes data element metadata. The information included in a data dictionary may help you establish the scope and characteristics of data elements and the management that governs their usage and application.

Why is a data dictionary important?

Data dictionaries are helpful for a variety of reasons. To summarize, they have the following characteristics:

• Assist in eliminating project data inconsistencies.
• Define conventions that will be utilized throughout the project to avoid confusion.
• Provide consistency in data collection and usage across the team.
• Make it easier to analyze data.
• Enforce the use of data standards

What are data standards?

Standardized data follow standards. Data are gathered, recorded, and represented in accordance with standards. Standards provide a common framework for interpreting and utilizing data sets.

Researchers in different fields must use comparable standards to know that the manner their data are collected and described will be consistent across different projects. Using Data Standards as part of a well-designed dictionary might help make your research data more accessible. It will guarantee that data will be identifiable and usable by others.

The key elements of a data dictionary

It is a document that explains the meaning of each attribute in a data model. An attribute is a database position that contains information. For example, if we wanted to represent the articles on this website, we could have attributes for article title, author, category, and content.

It is generally organized in a spreadsheet. The spreadsheet contains rows for each attribute, with columns labeled for each piece of information relevant to the attribute.

A data dictionary has two essential elements:

1. List of tables (or entities)
2. List of columns (or fields, or attributes)

Let’s look at the most frequent components included in the dictionary.

• Attribute Name – A distinguishing name that is used to identify each feature.
• Optional/Required – Whether information is necessary for an attribute before a record may be stored is indicated by the presence of this checkbox.
• Attribute Type – How you determine what data will be included in a field is defined by this setting. Text, numeric, date/time, enumerated list, look-ups, booleans, and unique identifiers are just a few possible data types.

A data dictionary may include the origin of the data, the table or concept in which the attribute is found, and additional information about each component.

Types of data dictionary

It’s possible to split the dictionary into two categories:

1. Active data dictionary
2. Passive data dictionary

Active data dictionary

When the data definition language (DDL) changes the database object structure, it must be reflected in the data dictionary. The job of updating the data dictionary tables for any modifications is solely that of the database in which the data dictionary is located.The data dictionary is automatically updated if created in the same database. As a result, there will be no mismatch between the actual structure and the data dictionary details. An active data dictionary is current at the time of writing this book.

System Catalog

It’s a term used to describe several things: the System Catalog, system tables, data dictionary views, etc. The System Catalog is a collection of system tables or views incorporated into a database engine (DBMS) to allow users to access data in the database. It also contains information about security, logs, and health.

Moreover, System Catalog has some standards, such as Information Schema.

Information Schema

The Information Schema is a popular System Catalog standard defined by SQL-92. It’s a unique schema named information_schema with preconfigured system views and tables. Despite being a norm, each vendor implemented this standard to some degree, adding its tables and columns.

Some of the tables in information_schema:

• tables
• columns
• views
• referential_constraints
• table_constraints

Passive data dictionary

Some databases include a dictionary in a separate, independent database only used to store dictionary components. It’s often saved as XML, Excel files, or other file formats.

In this scenario, a concerted effort is required to keep the data dictionary in sync with the database objects. A passive dictionary is what you’re dealing with here. There’s a chance that the database objects and the data dictionary won’t match in this instance. This kind of DD has to be handled with great sensitivity.

The passive data dictionary is distinct from the database and must be updated manually or with specialized software whenever the database structure changes.

A passive dictionary might be implemented in a variety of ways:

• A document or spreadsheet
• Tools
  • Data Catalogs
  • Data integration/ETL metadata repositories
  • Data modeling tools
• Custom implementations

Data dictionary example

You’re undoubtedly asking how everything fits together.

Here’s a look at an inventory list, a basic example of a data dictionary.

As you can see, a dictionary organizes critical information about each attribute in a business-oriented way. It also groups information that may be found in multiple documents and specifications, making it more straightforward for your database developer to create or change a database that fulfills company demands.

Functions of data dictionary

A dictionary may be used for a variety of things. The following are some important uses:

Data dictionary in database systems (DBMS)

The information about data structures is kept in special formats in most relational database management systems – predefined tables or views that contain metadata for each component of a database, such as tables, columns, indexes, foreign keys, and constraints.

A data-driven tool generates reports based on the database schema, including all parts of the data model and programs.

Data modeling

Data models can be constructed with the data dictionary as a tool. This may be accomplished using specialized data modeling software or simply a spreadsheet or document. In this instance, the dictionary acts as a specification of entities and their fields, assisting business analysts, subject matter experts, and architects in collecting requirements and modeling the domain. You’ll develop and deploy a physical database and application following this document.

Documentation

It is also possible to use a data dictionary as a reference and cataloging tool for existing data assets – databases, spreadsheets, files, etc.

With a few formats and programs, you can achieve this:

• You may export read-only HTML or PDFs from a DBMS with database tools.
• Excel spreadsheets that have been manually created and maintained.
• The data modeling tools utilize reverse engineering.
• Database documentation tools.
• Metadata management/data catalogs

All of these efforts are for healthy database management.

What is database management?

A database’s data can be organized, stored, and retrieved using Database Management. A Database Administrator (DBA) may use various tools to manage data throughout its lifecycle.

Designing, implementing, and supporting stored data to increase its value is the goal of database management. There are different types of Database Management Systems.

• Centralized: All data resides in one system handled by a single person or team. Users go to that one system to access the information.
• Distributed: The organization wanted a highly scalable system that allowed data to be accessed quickly.
• Federated: Data is extracted from your existing source data without the requirement for extra storage or replication of original material. It combines numerous independent databases into a single colossal item. This style of Database Architecture is ideal for integration projects involving many different types of data. The following are examples of federated databases:
  • Loosely Coupled: The relational structure of a component database is defined by its federated schema, which must be accessed via a multi-database language to access other component database systems.
  • Tightly Coupled: Components use separate processes to generate and publish into a connected federal schema.
• Blockchain: A decentralized database architecture that allows you to keep track of your finances and other transactions securely.

Do you think your data dictionary will lead the road to successful database management?

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'Threat dictionary' gauges cultural response to fear - Futurity: Research News - Dictionary

A new “threat dictionary” identifies language that shows when people feel threatened emotionally or physically and measures the magnitude of that perceived threat.

It’s an algorithmic tool that uses natural language processing to analyze texts.

One of the tool’s creators, Michele Gelfand, a professor of organizational behavior at Stanford Graduate School of Business, isn’t kidding when she asks if a person is an order Muppet or a chaos Muppet. She categorizes cultures and personalities on a spectrum from tight to loose and then examines how those differences affect nations, companies, families, and even individuals.

The two kinds of Muppets (first classified by Dahlia Lithwick in Slate in 2012) make for a pretty good proxy for this split.

Bert, Big Bird, and Kermit are rule followers. They tend to get anxious about unknown situations and aren’t big on spontaneous or rash decision-making. On the opposite end of the spectrum are Muppets like Ernie, Cookie Monster, and Animal. They’re more creative, but also quasi-unpredictable, and sometimes impulsive. Gelfand says she leans loose.

To find out what kind of Muppet you are, take her 20-question tight-loose quiz.

Beyond learning your Muppet-type, the loose-tight model provides a useful way to understand why culture and individuals land in different places on the continuum. The theory is deceptively simple. When groups experience chronic threats—think natural disasters, famine, invasions, or other hardships—stricter rules help them coordinate to survive. They tighten up, Gelfand explains. But groups that don’t experience chronic threat can afford to be more permissive.

Gelfand has been doing surveys and experiments across the globe to study the connection between threats and tightening. But she wanted a tool that could measure different kinds of threats over time and track how they correlate to cultural responses as well as how they predict political and economic shifts. Surprised to discover that no such tool existed, she decided to build one.

The resulting threat dictionary, created with researchers in computer science and psychology at the University of Maryland, College Park, appears in the Proceedings of the National Academy of Sciences.

The threat dictionary

Other researchers have developed dictionaries on other topics, but those efforts relied on people to come up with lists of words. Gelfand and her coauthors created their 240-word threat dictionary with text from Twitter, Wikipedia, and randomly chosen websites. Algorithms combed through the data, selecting words and plotting them on a graph, placing terms with similar meanings closer together.

The final list of words reads like an apocalyptic poem: attack, crisis, fear, frightening, injury, suffer, toxic, unstable.

The team then selected the words that most often co-occur across these platforms. They didn’t just choose synonyms, but terms that were often used in association with language that described threats. For instance, the term “unrest” is frequently used to describe an impending civil war. This approach was more comprehensive than purely human attempts and it allowed the dictionary to capture how people actually write about threats. The final list of words reads like an apocalyptic poem: attack, crisis, fear, frightening, injury, suffer, toxic, unstable.

The dictionary’s 240 words aren’t specific to any scenario and could be used to describe either interpersonal or external threats. They could just as soon describe the terror of a zombie uprising as the drama of a middle school dance. But they get at the underlying psychology of a society responding to threats that may be real or imagined.

The dictionary can also measure the relative magnitude of these threats and compare different levels of threat across texts and over time. That could help organizations, researchers, and societies understand their cultures and intentionally adapt to a given scenario.

Threats in US history

Gelfand and her colleagues tested the threat dictionary by feeding it information from three types of historical threats that the US has faced: violent conflicts like World War II, natural disasters like floods, and pathogens like COVID-19. Using a century’s worth of newspapers as well as stock market data, surveys that recorded attitudes toward immigrants, and language used in presidential speeches, the study examines how those threats predicted cultural, political, and economic shifts over the last 100 years.

Gelfand and her colleagues found that when people feel threatened either by a natural disaster, a disease outbreak, or a human enemy, they tighten up. Presidential approval rates go up, as do ethnocentrism and conservatism. But innovation suffers as cultural slack is picked up. During threat-heavy periods, fewer patents were filed and stock market prices were lower.

The researchers also showed that threatening language is contagious. Adding just a single threat-related word to a tweet about COVID increased the expected retweet rate by 18%.

Gelfand notes that there are exceptions to the threat-tightening link. She found that the US and other relatively loose countries have been slower to respond to the COVID pandemic and ultimately had more cases and deaths per capita. “Generally, loose cultures have had less threat in their histories,” she says. The United States hasn’t fought a war on its soil for over a century. “We haven’t had chronic invasions on our territory, so we’re not used to sacrificing a lot of liberty for constraint. It’s just not part of our cultural DNA.”

Other threats like 9/11 have caused Americans to tighten up in the past, but COVID-19 was different. The threat was invisible and abstract. And in some loose cultures, leaders ignored or downplayed the threat, which interrupted the typical tightening that naturally occurs.

Threatening language can manipulate us

On the other hand, Gelfand notes that leaders can manipulate threatening language in speeches or social media and can artificially tighten groups. In this way, a threat dictionary can help shine a light on how societies react when they feel threatened by identifying when and how often threats appear. Politicians, advertisements, and news reports often use fear to manipulate voters or rally people behind a cause.

“Culture’s invisible, but once we start measuring it, we can talk about it.”

But it’s hard to measure and study when and how much people feel threatened. “In cross-cultural psychology, we want to get as many measures as we can,” Gelfand says. That includes surveys, but also more unobtrusive tools like the dictionary, which she hopes will give researchers an empirical tool to evaluate this complex feeling more precisely and situate it within a larger social, political, and economic context.

It can also help elucidate how those cultural changes affect a company or nation by placing them in a larger social context. Researchers can correlate tightening or loosening with other indicators like stock market prices, public opinion polling, or investor behavior to see how threats affect different parts of society like the economy or immigration policy.

Looseness and tightness

The possible uses for the threat dictionary are vast, Gelfand says. It could be used to track when leaders inflate threats and which groups are labeled as dangerous. Researchers could analyze CEOs’ or officials’ speeches for threat mentions and compare them to fMRI images of what happens in peoples’ brains as they hear those terms.

Social media users could use it to be more conscious of how they’re participating in the spread of threatening messages and make choices about how much of that kind of language they want to see or what they want their kids to see. Gelfand’s threat barometer can be used to track how much threat one is exposed to on social media. The dictionary could also be combined with voting data to predict how a perceived threat might influence election results. Or it could examine how threatening language varies between different media outlets and how it affects the way they report the news.

Tightness versus looseness is a trade-off, Gelfand says, and it has to be balanced: “If you become extraordinarily tight or extraordinarily loose, that really causes a lot of problems.”

Unlike Muppets, who are entertaining because they rarely stray from their core characteristics, people and cultures can adapt to respond more effectively to difficult situations. Gelfand hopes the threat dictionary could help nations, companies, and individuals understand when they need to pivot. For more loose, chaotic types, this could mean tightening up to deal with a pandemic or war. For the tighter, orderly types, this could mean loosening up to create environments that encourage innovation and creative problem-solving.

The point, she says, isn’t that one type is better than the other. It’s the ability to titrate the right mix that really matters. “Culture’s invisible, but once we start measuring it, we can talk about it,” Gelfand says. “We can decide mindfully in what domains we want to tighten and in what domains we want to be loose.”

Source: Sara Harrison for Stanford University

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Mirror-Man: On Aaron Poochigian's Translation of Baudelaire - lareviewofbooks - Translation

A YOUNG MAN from the provinces arrives in the big city to make his reputation as a poet. He translates the work of others, composes beautifully crafted verse, and becomes a consummate chronicler of urban life. That is not Charles Baudelaire’s story. Baudelaire was born in Paris. As a teenager he began writing some of the poems that would evolve into Les Fleurs du mal, and later he translated Poe. The young man described is Aaron Poochigian, who was born in Grand Forks, North Dakota, trained as a Classicist, translated Sappho and Aristophanes, and writes about New York City (and beyond) like a jaundiced celebrator of its virtues and vices. And now he has translated one of his poetic forebears, Baudelaire (1821–’67). What Poochigian gives us in his Flowers of Evil are stylized, vigorous, clear, sturdy American poems, a recognizably 21st-century Baudelaire.

For a taste of his approach, consider Baudelaire’s introductory poem, “To the Reader” (“Au Lecteur”), taking the first stanza as a poetic core sample. Here is the late Richard Howard’s American Book Award–winning translation from 1982:

Stupidity, delusion, selfishness and lust
torment our bodies and possess our minds,
and we sustain our affable remorse
the way a beggar nourishes his lice.

Here is Walter Martin’s version from 1997:

Sin, stinting, senseless acts and sophistries
Pester the flesh and prey upon the mind;
We keep our stainless consciences maintained
Like indigents who fatten up their fleas.

Now Poochigian’s:

For all of us, greed, folly, error, vice
exhaust the body and obsess the soul,
and we keep feeding our congenial
remorse the same way vagrants nurse their lice.

Such remarkable variance of word choice. Until the fourth line one might almost assume the stanzas come from three different French poems. Only Poochigian uses “soul” and the four nouns in his first line. Howard and Poochigian choose “remorse,” while Martin changes the sense entirely to the awkward “stainless consciences.” There’s some confusion about the insect infestation: lice or fleas? Baudelaire gives us the indeterminant “vermine.” Howard selects “beggar” (singular) for Baudelaire’s “mendiants,” while Martin has the bureaucratic-sounding “indigents.” Poochigian wisely uses “vagrants,” which adds a suggestion of errancy and ephemerality. Best of all, Poochigian opens with the inclusive phrase “For all of us,” not those dutiful lists of nouns. He captures something quintessentially Baudelairean with the oxymoronic “congenial / remorse.” In his excellent introduction to Poochigian’s volume, Dana Gioia writes:

For Baudelaire, beauty exists in an endless dialectic between the spiritual and animalistic elements of human nature. The energy of that dialectic animates Baudelaire’s work. It also explains why his poetry is so difficult to interpret; it does not present static insights, but a dynamic relationship between contradictory forces.

That tense dance of opposites appears everywhere in Flowers of Evil. When it comes to sin and “transgression,” Baudelaire has an adolescent streak. You name it, he’ll try it: dope, whores, absinthe, Satan worship, any corruption of the human body and soul. He revels in offending bourgeois sensibilities. After his book was published in 1857, the poet, his publisher, and his printer all were prosecuted for offenses against public morals. More significantly, some of the poems still make for uncomfortable reading. In a poem Poochigian translates as “A Carcass” (“Une Charogne”), Baudelaire writes:

The blowflies in her bowels made a hum;
there also was a horde of seething
maggots flowing like a busy stream
across her ripped and living clothing.

And yet this bad boy was a strict formalist. In his “Note on the Translation,” Poochigian pledges his allegiance to that element of the work. The French originals are written largely in alexandrines, which he wisely has not attempted to replicate. Instead, he relies on English accentual-syllabics. Yes, he counts syllables but also pays attention to word stress and isn’t shy about using iambs. The effect is a more conversational reading of Baudelaire’s lines, with less stilted diction and syntax. To contemporary ears, Poochigian’s versions often sound “natural,” especially since his approach also leaves room for humor, as in these stanzas from “To One Who Is Too Cheerful” (“À Celle qui est trop gaie”):

Sometimes in green and pleasant places
to which I have lugged my great ennui,
I have suffered as, like irony,
rays of the sun chewed me to pieces.

And then the springtime greenery
so demoralized my heart
that I have ripped a flower apart
to punish Nature’s pomposity.

For all his outrageousness, Baudelaire remains a moralist. Yvor Winters observed that his poems often conform to a common 19th-century poetic structure: “[T]he account of an action, a situation, or an object followed by a moral tag.” Among the poems Winters prized above all others in any language was Baudelaire’s “Le Jeu,” translated by Poochigian as “Gambling.” He sets the scene: “pale, old courtesans” sit around the “green felt” listening to “the garish stones / and metals tinkle.” They are spectators at the roulette table, watching the “poets, who waste their sweat and earnings there.” Baudelaire’s speaker in turn watches the courtesans, “palsied by accursed diseases,” who watch the gamblers. The scene unfolds before his “visionary eyes,” as in a dream. Here is the final stanza:

I shuddered at my envy of that lot
dashing so rashly into the abyss.
Drunk on the blood down there, they choose to set
pain over death, Hell over nothingness.

Poochigian’s Baudelaire is evidence of an ongoing Golden Age of Translation from many languages, including Italian, German, and Russian. It’s a good time to be a reader. We obdurately monolingual Americans, of course, have much to lose, especially in the work of so musical a poet as Baudelaire. Our debt to translators like Poochigian, who are comparably sensitive to both sound and sense, is enormous. In his translation note, Poochigian tells us he has attempted to replicate “the almost magical effect of the originals and to render beautiful in English Baudelaire’s nontraditional beauties — disease, vice, intoxication, and decay.”

It helps that Poochigian is one of our finest young poets. A Baudelairean strain runs through his own work. A poem in his most recent collection, American Divine, is titled “The Satanists”:

hunkered with candles
and all the goodies
demons enjoy,
in the hopefully hexed
and totally scary
dead lot next
to the cemetery.

And here’s a memorable dog in “My Political Poem,” from the earlier Manhattanite: “So cute — one-eyed, scab-nostriled, stumpy-tailed.” Appealing and grotesque, a combination in which his French forebear specialized. Present in Poochigian’s poems, including the translations, is what Baudelaire elsewhere calls “the heavy darkness of communal and day-to-day existence,” but made lighter, funnier, bouncier, with the gravitas muted. W. S. Di Piero has written of Thom Gunn: “He admired Ben Jonson and Baudelaire because their little-furnace forms — those clocking, rhyming meters — could contain fevered appetites and personal anarchy.” That’s Poochigian and his calibrated tension between tidy form and riot: “furnace forms,” with equal emphasis on both words.

Earlier I quoted Poochigian’s opening stanza from “To the Reader.” Here is his version of the poem’s final stanza, including Baudelaire’s most familiar lines:

Boredom! Moist-eyed, he dreams, while pulling on
A hookah pipe, of guillotine-cleft necks.
You, reader, know this tender freak of freaks —
Hypocrite reader — mirror-man — my twin!

Poochigian’s rendering of “mon semblable” as “mirror-man” is inspired. As Gioia points out, the poem is written in the first-person plural, blurring the identities of poet and reader. All of us are implicated.

¤

Patrick Kurp is a writer living in Houston and the author of the literary blog Anecdotal Evidence.

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Text-to-911 translation now available - Seymour Tribune - Translation

The Indiana Statewide 911 Board, in collaboration with INdigital and the state treasurer’s office, recently announced another tool that enhances communications between non-English-speaking citizens and emergency services.

Since 2019, dispatchers at all of Indiana’s public safety answering points have had access to Language Line, which provides voice translating services for 911 callers. Over the past three years, Indiana telecommunicators have used voice translation services for nearly 70 of the more than 250 languages available.

Spanish is the most frequently translated language used, comprising of 91% of the translation calls. Marion, Elkhart, Allen, White and Tippecanoe counties are the top five users of the system.

Speaking at the Metropolitan Emergency Services Agency on March 30, Treasurer Kelly Mitchell, chairwoman of the state 911 board, unveiled significant enhancements to the Text-to-911 system.

Citizens can now send text messages in their native language directly to 911 for help, and they will be automatically translated for the dispatcher. As the dispatcher responds, it will be automatically translated back into the native language of the sender. There are 108 languages available for Text-to-911 translation.

The Jackson County Sheriff’s Department is among those able to translate other languages through the 911 texting system, according to a news release from the department.

“Text-to-911 enables direct access to emergency services for those who are deaf or speaking-impaired, having a medical emergency that prevents them from being able to speak or in a situation where making a voice call would put them in danger,” Mitchell said.

“We’ve already seen the benefits of texting to 911,” she said. “It allows people in sensitive situations to communicate with law enforcement, and now, we are removing the language barriers to those services.”

In 2014, Indiana was one of the first states to begin implementing Text-to-911, and by 2016, all 92 counties had the capability.

As a result, Indiana telecommunicators have processed more than 1.3 million inbound and outbound text sessions.

“With technology constantly evolving, this upgrade shows why Indiana is on the forefront in providing 911 services to our non-English-speaking citizens,” said Ed Reuter, executive director of the state’s 911 board. “This new translation upgrade will help bridge the communication gap and speed up sending emergency services when every second counts.”

Mark Grady, chief executive officer of INdigital, said his company works to improve 911 service every day.

“Strong state programs like Indiana lead the nation with good legislation, targeted funding and letting us build better systems,” he said. “Our goal is for everyone to have access to 911 when they need it most. Bridging language barriers and providing more ways to communicate are essential in today’s world.”

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The Mindful Dictionary:A is for Appreciate - Maldon and Burnham Standard - Dictionary

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The Mindful Dictionary:A is for Appreciate  Maldon and Burnham Standard

Hacker Dictionary: RS-485 Will Go The Distance - Hackaday - Dictionary

RS485 is a communication standard that should be part of the advanced hardware hacker’s arsenal; it’s not commonly encountered, but powerful exactly when you need it. It’s a physical layer interface for wired communications that uses a single differential pair for noise immunity, has good long-distance properties, and allows many connections to a single bus. Because of that, you will encounter it in security systems and even cameras, wired sensor networks, DMX512 lighting and all sorts of industrial electronics. For our hobbyist goals, you can absolutely use RS485 to build your home (or room) automation system, or a relatively large robot – without all those worries that wireless brings.

The name might remind you of RS232, and that’s because both RS232 and RS485 are standards that come from EIA (Electronics Industries Alliance). It also might remind you of RS422, if you’ve ever seen this name mentioned online – RS422 and RS485 are closely intertwined, sharing most of the physical layer, and I’ll show how exactly they relate.

At its simplest, a RS485 link is akin to a UART communications channel, but differential and half-duplex, with TX and RX combined into a single communications line. Bytes sent as unclocked data at a pre-arranged baud rate, so your USB-UART adapter or MCU’s UART peripheral will work for most RS485 purposes. Just like with UART, there are only a few commonly used baud rates, so it should be easy to guess. The differential signal means that you will need to use special transmitters and receivers for working with RS485 links – they aren’t pricey, so it’s wise to have a few in stock before the day when you could really use it.

One of the main benefits of  RS485 is that you can put multiple devices on a single link. This is a pleasant difference from logic-level UART or RS232, especially for our sensor and other smart device network building needs. The tradeoff is that an RS485 link is half-duplex – that is, two or more devices cannot transmit at the same moment of time.

If you ever really need a full-duplex connection, where devices X and Y might want to transmit without regard for each other, you will want to use two RS485 links – one link for a “X transmits, Y receives” direction and other for the “Y transmits, X receives” direction, point-to-point style. Congratulations, you’ve invented RS422, but you’ve lost the very useful bus nature of RS485.

Signals are transmitted differentially. In place of one signal, there are two signals: one is always opposite the other – when you transmit a high logic level, line A goes high and line B goes low, and when you transmit a low logic level, line A goes low and line B goes high. The receiver doesn’t measure the absolute level of the signals relative to ground – instead, it measures the difference between them. We have talked about differential pairs before, explaining their benefits like high noise reduction. Using differential pairs is what allows for RS485 links hundreds of meters long that you will see people online brag about building!

One fun part about RS485 is the A/B naming conventions. In the last paragraph, I’ve used “A” and “B” as “non-inverting” and “inverting” signals respectively – that is, voltage on “A” has the same polarity as the logic level of the signal transmitted, but voltage on “B” is the opposite of it.

The RS485 standard, as it’s written, actually has the opposite meaning for these two – “A” is inverting and “B” is non-inverting. However, the RS485 transciever makers have all (consistently) reversed them relative to the standard, to the point where Wikipedia has a good few paragraphs complaining about it. When it comes to the naming convention being used in this article, I will use the signal names you will actually deal with when it comes to RS485 ICs and devices, as opposed to the ones defined in the standard but not actually respected by devices you will encounter. It might be better if the world standardized on “D+” and “D-” as with USB, but that ship has sailed.

The difference between two signals, rather than their voltage relative to a common ground, is what the controller actually cares about. What happens if they’re close to each other – say, there’s no transmitter driving the line at the moment? If the difference between A and B is within 200 mV, the signal is considered invalid, and your receivers might get confused, or, at best, reject it. To avoid this, biasing resistors are typically used – a pullup on A and a pulldown on B. The typical biasing resistor values are calculated to create a voltage a bit over 200 mV (to account for noise) on receiver inputs after accounting with the cable impedance and termination resistors – essentially, calculating a three-resistor voltage divider.

Common practice is to put two resistors in one spot, and have them do all the biasing work. You can absolutely ballpark something like 500 ohms worth of pull, and this appnote has a straightforward formula on page 4 if you’d like to know more – a simple resistor divider calculation is all it takes. There’s more to the bus, however – let’s dive into the layout and termination requirements.

In differential links like this, especially as speeds get higher, impedance starts to matter – which, in large part, is a requirement for the cabling you use. For a start, it has to be a twisted pair. The recommended impedance for RS485 links is 120 ohms and that’s what RS485 hardware is typically designed for, but for many hobbyist applications, you can absolutely use one of the pairs in an Ethernet cable (100 ohms) or a decent USB cable (90 ohms) and call it a day.

For impedance matching and reflection dampening reasons, RS485 also requires that you add termination resistors at the ends of the network – they’re typically 120 ohms. Typical RS485 modules you can get come with 120R termination resistors, and you likely won’t need to adjust them to match your cable’s impedance – but you will need to remove the termination resistors that are not on the ends of the daisy chain! Interested in more explanations of why termination matters, with pretty graphs and explanations of all the different types of termination possible? This appnote will help you, too.

The RS485 bus doesn’t lend itself to stubs, and especially not to star topology networks – pulling the same link into multiple different directions is heavily discouraged due to reflections caused by signal coming back from ends of multiple different branches at once, and difficulties properly terminating such a topology. The best network will result from daisy-chaining the devices, as in, having them in a straight line, with RS485 devices connected inline, stubs as short as reasonably possible — under six inches is the usual guideline, but less is better.

So how do you actually get into RS485, as a hobbyist just learning about the powers it gives you? If you look up “RS485” at your online retailer of choice, you will encounter these cheap elongated blue modules with pin headers and a terminal block – and feel free to just get those. Most of them have clones of the MAX485 IC – one of the many IC designs for talking RS485 and certainly a staple of RS485 hardware, others being generally pin-compatible for the same feature set, like SN75176 and SP485.

These PCBs come with 120 Ω termination resistors and 20 kΩ biasing resistors – you will likely want to change these. Remove the termination resistors for any modules not at the ends of the link, and replace biasing resistors with those that get you to a stable bus idle voltage point – a pair of 560 Ω resistors on one of the modules will do well for biasing.

The MAX485 works with a single RS485 link, so it is half-duplex: you have to switch it between receiving and transmitting. On the MAX485, transmitter and receiver enable inputs are two different pins, but basically everybody joins them into one pin. This is possible because the RE (Receiver Enable) signal is inverted, and this lets you switch between transmit and receive with a single GPIO. Essentially, you short pins 2 and 3 of the MAX485 together, either with a jumper wire or with a tactically placed drop of solder, then set them to a low logic level for receiving or high logic level for transmitting with a GPIO. If you’re using a USB-UART or UART peripheral, check if you have the RTS signal available to you – it can be directly wired to a RS485 transceiver’s ~RE and DE for seamless RS485 link operation!

You can buy these “MAX485” modules and mostly be set, but the ICs on them are clones and might burn out on you every now and then. Getting some legit MAX485 ICs from a reputable store and replacing them with your hot air station of choice is a good idea if you want your setup to be reliable. One of the problems with MAX485 is that it requires 5 V and might not work at 3.3 V, so you might as well get some MAX3485 chips and solve both of these problems in one go. Otherwise, if you got a Raspberry Pi in one hand and a cheap “MAX485” module in the other, feel free to use any of the level shifting options, from using one of the usual logic level shifters to simply pulling the VCC of MAX485 down with a diode.

With all this customization and rework, you’re probably thinking you might as well design your own RS485 interface. If you’ve already committed to a PCB design for the project, you’re probably right.

The RS485 physical layer lets you put many devices on the same link, like I2C. You cannot do that with three devices that have UART. The requirement, again, is that you only ever have one transmitter active at a time – so, by default, you’d have all transmitters on all devices disabled, and only enabled at a time when one device needs to say something.

The maximum number of devices that you can put on a single bus is described through the concept of “unit load”, a function of the input impedance of receivers and the biasing. In other words, receivers put a certain amount of load on the transmission line, and when the line is loaded too much, the signal levels get too low. The unit load values of your ICs can be found in their respective datasheets, with typical values resulting in up to 32 receivers on a single bus, and available transceiver ICs with low enough unit load that lets you get that number up to 256.

For your own RS485 communications on a multi-drop network, you’d want some kind of transmission protocol that has coexistence and addressing in mind. There’s one popular and powerful option you’ll want to know about, and that is Modbus RTU! It is a data protocol you can use on top of RS485, suited for links with a single controller and multiple peripherals. It’s a commercially successful yet open protocol – which is to say, you can speak Modbus in between your own devices, but also to a large range of devices like heavy-duty machinery or energy meters. There’s plenty of decent libraries for Modbus communications for environments like Python and Arduino to do most of the job for you.

You might notice that the “single controller, multiple peripherals” principle is similar to I2C, and that’s not the only way where Modbus and I2C are alike. For a start, Modbus peripherals, too, have addresses. The way that data is accessed in Modbus is also similar to the register-based system that the more advanced I2C devices have: each Modbus device has registers you can read from or write into. Writable registers tend to be referred to as coils, read-only registers tend to be referred to as inputs, and there’s generally agreed-upon register address ranges telling you at a glance which are which. When building makeshift Modbus devices, however, you are free to break these conventions if it suits you.

“Do you need a ground connection for a RS485 link?” is a hotly debated question, just like “do I need to tie my USB port shield to ground”. You will see a lot of people say that a ground reference isn’t technically needed – after all, it’s a differential signal, and at most, shielding could be called for. This will generally work, even! However, lack of ground can result in high common-mode (relative to ground) offset voltage on one of the ends, and while RS485 transceiver ICs can handle quite a bit of that, it can cause issues depending on the kind of devices in your network.

If you’re running a link between devices powered by un-earthed wall-wart PSUs, pulling a common voltage reference along is likely wise. The same goes for a network of battery-powered devices, since voltage induced on one end of the network will happily go onto transceiver inputs of other devices that, in turn, might be capacitively coupled to somewhere else. Not to mention that noise finds a way.

If you are using earthed PSUs on both sides, however, running a separate ground line might create a ground loop. If the “ground” potential at two different locations is wildly different, you may also end up pulling considerable, undesirable current through the common path. Remeber that the two transceivers need a common middle voltage reference, but it need not be “ground”.

If grounding had straightforward answers, we hackers wouldn’t have so many conflicting opinions about it. In case your ground issues get really unmanageable, you can get isolated RS485 transceivers, or, on a budget, use a few 6N137 high-speed optocouplers, maybe even one of those isolated DC-DCs. Typically, there’s solutions available for any RS485 problems you encounter, and people have made RS485 links work in pretty grim circumstances.

If you experience a noticeable amount of data loss or corruption, it’s worth poking your transmission line with a scope or a multimeter. Is the bus idle state within voltage margins, at different points in the network? Do you have ringing on the signal, and how “bad” is it relative to the norm and the signal levels you’d expect? Does ringing change depending on how far the device is in the chain? Echo your Modbus (or other protocol) packets into a debug console – do they arrive intact?

With this knowledge of RS485, you won’t just be able to gain control of more and more powerful devices out there, you will also figure out some fun things that will help you in other areas. For instance, you don’t have to put UART-like communications through a RS485 transceiver, you can simply use it for transmitting the state of a GPIO in a noisy environment. Or you can use an RS485 transmitter to dramatically extend range and stability of WS2812 LED protocol communications, especially when you have high-voltage lines running close to your LED strips.

There’s an idea floating around that you could use the transmitter section of an RS485 driver IC to drive small vibromotors as an improvised cheap H-bridge – and get yourself some fancy haptics-capable hardware as a result. Small-footprint H-bridges, especially for low-power electronics, can get expensive, chip shortages don’t help either – yet RS485 transceivers are cheap and still abundant. Who wants to bet that this will work?

RS485 is an underappreciated topic, and while wireless links are enticing, there’s plenty of space for good old rugged differential communications. Whether you’d like a protocol you can understand, an interference-resilient communications channel, or an inherently secure physical layer for your network, RS485 is here for you. With one more tool in your arsenal, may you design wired long-distance links like never before.

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