原创 The microprocessor at 40 - The dawn of electronics (Part 2)

It's difficult to track down the history of the resistor, but Georg Ohm published his findings that we now understand as Ohm's Law in 1827. So the three basic passive elements—resistor, capacitor, and inductor—were understood at least in general form in the early 19th century. Amazingly it wasn't till 1971 that Leon Chua realized a fourth device, the memresistor, was needed to have a complete set of components, and another four decades elapsed before one was realized.

Michael Faraday built the first motors in 1821, but it wasn't until the 1860s that James Maxwell figured out the details of the relationship between electricity and magnetism; 150 years later his formulas still torment electrical engineering students. Faraday's investigations into induction also resulted in his creation of the dynamo. It's somehow satisfying that this genius completed the loop, building both power consumers and power producers.

None of these inventions and discoveries affected the common person until the commercialization of the telegraph. Many people contributed to that device, but Samuel Morse is the most well-known. He and Alfred Vail also critically develop a coding scheme—Morse Code—that allowed long messages to be transmitted over a single circuit, rather like modern serial data transmission. Today's Morse code resembles the original version but with some substantial differences. SOS was dit-dit-dit dit-dit dit-dit-dit instead of today's dit-dit-dit dah-dah-dah dit-dit-dit.

The telegraph may have been the first killer app. Within a decade of its commercialization, over 20,000 miles of telegraph wire had been strung in the U.S., and the cost to send messages followed a Moore's Law-like curve.

The oceans were great barriers in these pre-radio days, but through truly heroic efforts Cyrus Field and his associates laid the first transatlantic cable in 1857. Consider the problems faced: with neither active elements nor amplifiers a wire 2,000 miles long, submerged thousands of feet below the surface, had to faithfully transmit a signal. Two ships set out and met mid-ocean to splice their respective ends together. Sans GPS, they relied on celestial sights to find each other. Without radio-supplied time ticks, those sights were suspect (four seconds of error in time can introduce a mile of error in the position).

William Thomson, later Lord Kelvin, was the technical brains behind the cable. He invented a mirror galvanometer to sense the miniscule signals originating so far away. Thomson was no ivory-tower intellect. He was an engineer (at that point in life) who got his hands dirty. He sailed on the cable-laying expeditions and innovated solutions to the problems encountered.

While at a party celebrating the success, Field was notified that the cable had failed. He didn't spoil the fun with that bit of bad news. It seems a zealous engineer thought if a little voltage was good, 2,000 would be better. The cable fried. This was not the first nor the last time an engineer destroyed a perfectly functional piece of equipment in an effort to "improve" it.

Amazingly, radio existed in those pre-electronic days. The Titanic's radio operators sent their dit-dit-dit dah-dah-dah dit-dit-dit with a spark gap transmitter, a very simple design that used arcing contacts to stimulate a resonant circuit. The analogy to a modern AM transmitter isn't too strained: today, we'd use a transistor switching rapidly to excite an LC network. The Titanic's LC components resonated as the spark rapidly formed, creating a low-impedance conductive path, and extinguished. The resulting emission is not much different from the EMI caused by lightning. The result was a very ugly wide-bandwidth signal, and the legacy of calling shipboard radio operators "sparks."

TV, of a sort, was possible in the late 1800s, although it's not clear if it was actually implemented. Around 1884, Paul Nipkow conceived of a spinning disk with a series of holes arranged in a spiral to scan a scene. In high school I built a Nipkow Disk, although used a photomultiplier to sense the image and send it to TTL logic that reconstructed the picture on an oscilloscope. The images were crude, but recognizable.

The next killer app was the telephone, another invention with a complex and checkered history. But wait—there's a common theme here, or even two. What moved these proto-electronic products from curiosity to wide acceptance was the notion of communications. Today it's SMS and social networking; in the 19th century it was the telegraph and telephone. But it seems that as soon as any sort of communications tech was invented, from smoke signals to the Internet, people were immediately as enamored with it as any of today's cell-phone obsessed teenagers.

The other theme is that each of these technologies suffered from signal losses and noise. They all cried out for some new discovery that should amplify, shape and improve the flow of electrons. Happily, in the last couple of decades of the 1800s inventors were scrambling to perfect such a device. They just didn't know it.