Saturday, December 15, 2012
  Before Morse 1

The basic idea of mechanical signaling was well-known in Europe before electricity arrived. Mirror-based semaphore systems had been used for a century in France and England. So in 1820, when Oersted figured out that an electric current passing through a coil of wire could move an iron bar, the next step was obvious to many inventors and investors.

Charles Wheatstone, a 'shy sensitive boy' from a musical family, was one of many who picked up the notion. He had already made some mechanical gadgets to amplify and carry sound, working from his musical genes.

Given his acoustic nature, it's sort of surprising that his telegraphs were so thoroughly visual.... but maybe not. All the early telegraphs were visual, using keyboards for sending and dials, pens or printers for receiving. These were intended for personal use by untrained people. After Morse's pen-based system was established, the operators realized they could understand the patterns better by ear. (And that's not surprising, since our hearing mechanism is built for language.) This realization quickly led to a switch from personal use by untrained people to centralized use by professionals who mastered the Code. Keyboards, dials and printers quickly disappeared, and simple keys and sounders became universal. Visual telegraphy might have developed directly into something like today's computer networks, but the auditory Code took it in a different direction, more of a public service utility.

Wheatstone connected up with the more practical and business-oriented William Cooke in 1835, and a series of commercially usable telegraphs followed. The first type used electromagnetism directly and simply, with five compass needles responding in opposite directions to opposite currents. Two wet cells powered the sender. A center 'ground' made it possible to energize each of the 5 magnets in opposite directions.

The keyboard continued the two-sided logic. The front row of keys ran through a bar connected to the positive side of the batteries, and the back row ran through a negative-powered bar. When you pushed on one key, it connected either negative or positive voltage to a spring that fed one of the magnets. [Note: the unit I copied for this model had 6 buttons in each row; it appears that the 6th button is a dummy or perhaps drove an alarm of some sort.]

Each letter is indicated by two needles leading along the diamond patterns to a letter, requiring a two-key 'chord' on the keyboard.

Here we have E indicated by positive current to the 3rd magnet and negative current to the 1st magnet.

This is a wildly inefficient way of using the available parts. Five needles with three positions should create 243 patterns [from 3 * 3 * 3 * 3 * 3]. That would accommodate upper and lower case letters, numbers, and punctuation easily. But the diamond uses only 20 of the possible patterns, not even 26. Users must have developed a set of altered spellings to work around the missing letters. Apparently Wheatstone thought an easily read 'map' was critically important.

Note the six wires leading out the right side. Five active wires capable of carrying negative or positive voltage, and one ground. The receiving unit, identical to the sender, would pick up the combinations and show them on its needles.

This meant you'd need five wires for EACH individual pair of sender and receiver.

In modern terms this system used 'parallel data transfer'. Each letter could be formed and sent almost instantly, which seemed like an advantage in theory. But 'serial transfer' telegraphs won the game despite their comparative slowness. A serial system takes a finite time to form the pulse pattern for each letter, but it requires only one wire. In real life the materials and labor involved with running wires and selecting circuits made five-wire systems wildly expensive. (Five times the copper, five times as many insulators, five times as much space on each pole, five times as much overhead congestion in cities.... )

Polistra is unhappy with the keyboard for obvious reasons....

So she trained a pair of bees [who know something about magnetic signaling!] to perform an example phrase. The red-eyed bee takes care of the positive (front) keys, while the blue-eyed bee takes care of the negatives.

The five-needle telegraph was clearly meant to be home furniture rather than an industrial mechanism. Reminds me of the first generation of personal computers, with keyboard and screen in one unit.

Bilateral symmetry seems to have been a strong theme for Wheatstone. Later on, he was responsible for one HUGELY IMPORTANT idea that resonates through all electronic circuitry. He developed the idea of differential measurement, using symmetry to balance out imperfections in the tools and conditions.

It's an old idea in measuring weight. By putting a known weight in one pan of a balance scale and the unknown in the other pan, you eliminate everything but mass. Local gravity is the same for both, friction affects the single pivot point for both; wind and humidity affect both sides the same way. Though difference measurement is intuitive in that one case, it took some highly non-intuitive tricks to make it work with electricity. The 'Wheatstone bridge' isn't used much in its original form, but the notion of differential measurement spawned the Operational Amplifier, which now forms the core of most analog circuitry.

More broadly, any time you have a 'processing element' of any type, a balanced circuit eliminates non-linear effects. Push-pull amplifiers, the long-tailed pair, CMOS digital devices.

Finally, Nature had the idea first. Most of our neurons are built as comparators or balances, with excitatory inputs and inhibitory inputs.

Wheatstone's telegraph faded after a while, but his balanced-circuit idea is one of the grandest and deepest of all inventions, right up there with fire and the wheel.

= = = = =

Later artistic note for Poser types: I've released this model on my ShareCG page, along with the Breguet system and the Gray telautograph.

<< Home

blogger hit counter
My Photo
Location: Spokane

Polistra was named after the original townsite of Manhattan (the one in Kansas). When I was growing up in Manhattan, I spent a lot of time exploring by foot, bike, and car. I discovered the ruins of an old mill along Wildcat Creek, and decided (inaccurately) that it was the remains of the original site of Polistra. Accurate or not, I've always liked the name, with its echoes of Poland (an under-appreciated friend of freedom) and stars. ==== The title icon is explained here. ==== Switchover: This 2007 entry marks a sharp change in worldview from neocon to pure populist. ===== The long illustrated story of Polistra's Dream is a time-travel fable, attempting to answer the dangerous revision of New Deal history propagated by Amity Shlaes. The Dream has 8 episodes, linked in a chain from the first. This entry explains the Shlaes connection.

My graphics products:

Free stuff at ShareCG

And some leftovers here.

March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / May 2007 / June 2007 / July 2007 / August 2007 / September 2007 / October 2007 / November 2007 / December 2007 / January 2008 / February 2008 / March 2008 / April 2008 / May 2008 / June 2008 / July 2008 / August 2008 / September 2008 / October 2008 / November 2008 / December 2008 / January 2009 / February 2009 / March 2009 / April 2009 / May 2009 / June 2009 / July 2009 / August 2009 / September 2009 / October 2009 / November 2009 / December 2009 / January 2010 / February 2010 / March 2010 / April 2010 / May 2010 / June 2010 / July 2010 / August 2010 / September 2010 / October 2010 / November 2010 / December 2010 / January 2011 / February 2011 / March 2011 / April 2011 / May 2011 / June 2011 / July 2011 / August 2011 / September 2011 / October 2011 / November 2011 / December 2011 / January 2012 / February 2012 / March 2012 / April 2012 / May 2012 / June 2012 / July 2012 / August 2012 / September 2012 / October 2012 / November 2012 / December 2012 / January 2013 / February 2013 / March 2013 / April 2013 / May 2013 / June 2013 / July 2013 / August 2013 / September 2013 / October 2013 / November 2013 / December 2013 / January 2014 / February 2014 / March 2014 / April 2014 / May 2014 / June 2014 / July 2014 / August 2014 / September 2014 / October 2014 / November 2014 / December 2014 / January 2015 / February 2015 / March 2015 / April 2015 / May 2015 / June 2015 / July 2015 / August 2015 / September 2015 / October 2015 / November 2015 / December 2015 / January 2016 / February 2016 / March 2016 / April 2016 / May 2016 / June 2016 / July 2016 / August 2016 / September 2016 / October 2016 / November 2016 / December 2016 / January 2017 / February 2017 / March 2017 /

Major tags or subjects:

Carbon Cult
Defensible spaces
Experiential education
Grand Blueprint
Гром победы
Language updates
Natural law = Sharia law
New toys

Powered by Blogger