Pennywhistle modem

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The Pennywhistle was an early acoustic coupler modem originally designed and built by Lee Felsenstein in 1973, and later commercialized and offered for sale in 1976. It was one of the earliest modems available for hobbyist computer users. [1] Like most acoustic coupler modems, the Pennywhistle was replaced by the Hayes Smartmodem and similar models from the early 1980s.

Acoustic coupler communication device

In telecommunications, an acoustic coupler is an interface device for coupling electrical signals by acoustical means—usually into and out of a telephone.

Modem Device that modulates an analog carrier signal to encode digital information

A modem is a hardware device that converts data between transmission media so that it can be transmitted from computer to computer. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals from light-emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

Lee Felsenstein Computer pioneer

Lee Felsenstein is an American computer engineer who played a central role in the development of the personal computer. He was one of the original members of the Homebrew Computer Club and the designer of the Osborne 1, the first mass-produced portable computer.

Contents

History

Prior modem

As part of the effort that would lead to the Community Memory bulletin board system, Lee Felsenstein had found an Omnitech modem ("or something like that"). [2] Designed to operate at rates as high as 300  bits per second (bit/s), the modem was able to change its speed to match conditions or differences in the modems at either end. In general it was good for only 100 bit/s, the speed that was used for much of its operational life. The modem was attached to a Teletype Model 33 ASR machine at Leopold's Records in Berkeley, California and connected to the SDS 940 mainframe computer in San Francisco. [2]

Community Memory

Community Memory (CM) was the first public computerized bulletin board system. Established in 1973 in Berkeley, California, it used an SDS 940 timesharing system in San Francisco connected via a 110 baud link to a teleprinter at a record store in Berkeley to let users enter and retrieve messages. Individuals could place messages in the computer and then look through the memory for a specific notice.

A Bulletin Board System or BBS is a computer server running software that allows users to connect to the system using a terminal program. Once logged in, the user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging messages with other users through public message boards and sometimes via direct chatting. In the early 1980s, message networks such as FidoNet sprung up to provide services such as NetMail, which is similar to email.

Teletype Model 33

The Teletype Model 33 is an electromechanical teleprinter designed for light-duty office. It is less rugged and less expensive than earlier Teletype machines. The Teletype Corporation introduced the Model 33 as a commercial product in 1963 after being originally designed for the US Navy. There are three versions of the Model 33:

New design

Felsenstein was unimpressed by the Omnitech design, especially its price of $300, [2] and convinced himself he could design a better version. He found that one half of the design problem was easy; generating the proper tones for transmission was simple. The other half of the problem was much harder; listening to the incoming signal and discriminating between the tones for "one" and "zero". The traditional solution was to generate a local reference tone and compare it to the incoming signal, but this was subject to many problems, from noise or distortion on the line, to drifting of the local tone due to events as mundane as temperature changes. [3]

Noise Unwanted sound

Noise is unwanted sound judged to be unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound.

Distortion is the alteration of the original shape of something. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal representing sound or a video signal representing images, in an electronic device or communication channel.

Felsenstein found two key improvements that led to a dramatically less expensive and more reliable design. The first was to ignore the idea of a variable baud rate, which was useful in some contexts, but not when used purely for data communications over known-good lines. [3] The other improvement, which would prove key to the design, was to use the incoming signal itself as the reference tone. While working at Ampex, Felsenstein had learned that the signal would always return to a "one" tone between sending bits of data; his new design looked for these signals and used them to resynchronize a local phase locked loop (PLL). [3] The system stored the "one" voltage generated by the PLL on a capacitor and set the threshold voltage to a fixed offset. The capacitor would slowly recharge and be reset by the next "one' voltage.

Ampex company

Ampex is an American electronics company founded in 1944 by Alexander M. Poniatoff as a spin-off of Dalmo-Victor. The name AMPEX is a portmanteau, created by its founder, which stands for Alexander M. Poniatoff Excellence. Today, Ampex operates as Ampex Data Systems Corporation, a subsidiary of Delta Information Systems, and consists of two business units. The Silicon Valley unit, known internally as Ampex Data Systems (ADS), manufactures ruggedized, high-capacity, high-performance digital data storage systems capable of functioning in harsh environments on land, in the air, at sea, and in space. The Colorado Springs, Colorado unit, referred to as Ampex Intelligent Systems (AIS), serves as a laboratory and hub for the company’s line of industrial control system cyber security products and services and its artificial intelligence/machine learning technology which is available across all of the company’s products.

These improvements meant the modem was able to follow changes in the reference tone no matter what the source of that drifting was, local or remote. It also eliminated the need for a local tunable oscillator, reducing the price of the system.

Commercialization

In 1976, Felsenstein was visiting "the junk man", Marty Spergel of M&R Electronics. Felsenstein had been talking about building a design for a data terminal he called the Tom Swift Terminal, but the design wasn't ready for development. Felsenstein then asked if Spergel would be interested in a related project, a modem that he had previously designed. Spergel was able to cobble together a version of the modem for a price of $109. [4]

The Processor Technology VDM-1, for Video Display Module, was the first video card for S-100 bus computers. Created in 1975, it allowed an S-100 machine to produce its own display, and when paired with a keyboard and their 3P+S card, it eliminated the need for a separate video terminal. Using a 7 x 9 dot matrix and ASCII characters, it produced a 64-column by 16-row text display.

The two then sent a copy of the schematics to Les Solomon at Popular Electronics magazine, where it was featured on the cover of its March 1976 issue. [5] M&R offered the Pennywhistle in kit form for $129.95, or fully assembled for $225. It was offered for sale for several years. [6] For comparison, the Novation CAT was listed at $179 in 1981 after several years of falling electronics prices. [7]

A schematic, or schematic diagram, is a representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the schematic is intended to convey, and may include oversimplified elements in order to make this essential meaning easier to grasp. For example, a subway map intended for passengers may represent a subway station with a dot. The dot is not intended to resemble the actual station at all; instead, it aims to give the viewer information without unnecessary visual clutter. A schematic diagram of a chemical process uses symbols in place of detailed representations of the vessels, piping, valves, pumps, and other equipment that compose the system; in so doing, it emphasizes the functions of these individual elements--and the interconnections among them--and suppresses their particular physical details. In an electronic circuit diagram, the layout of the symbols may not look anything like the circuit as it appears in the physical world: instead of representing the way the circuit looks, the schematic aims to capture, on a more general level, the way it works.

<i>Popular Electronics</i> IT Company

Popular Electronics is an American magazine published by John August Media, LLC, and hosted at TechnicaCuriosa.com. The magazine was started by Ziff-Davis Publishing Company in October 1954 for electronics hobbyists and experimenters. It soon became the "World's Largest-Selling Electronics Magazine". In April 1957 Ziff-Davis reported an average net paid circulation of 240,151 copies. Popular Electronics was published until October 1982 when, in November 1982, Ziff-Davis launched a successor magazine, Computers & Electronics. During its last year of publication by Ziff-Davis, Popular Electronics reported an average monthly circulation of 409,344 copies. The title was sold to Gernsback Publications, and their Hands-On Electronics magazine was renamed to Popular Electronics in February 1989, and published until December 1999. The Popular Electronics trademark was then acquired by John August Media, who revived the magazine, the digital edition of which is hosted at TechnicaCuriosa.com, along with sister titles, Mechanix Illustrated and Popular Astronomy.

Novation CAT

Novation was an early modem manufacturer whose CAT series were popular in the early home computer market in the late 1970s and early 1980s, notably on the Apple II. The Hayes Smartmodem 300, introduced in 1981, helped kill off Novation and many other early modem companies over the next few years.

Description

Like other acoustic coupled modems, the Pennywhistle design was dominated by the two large rubber cups on the top of the device that were used to hold the handset of a standard Western Electric phone. The Pennywhistle had a "step" cut into the front of the case where the various control switches were located, and the RS-232 port projected directly out of the front of the case.

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References

Notes

  1. ↑ Roy Allan, "A History of the Personal Computer: The People and the Technology", Allan Publishing, 2001, pg. 17
  2. 1 2 3 Crosby, "ON LINE AT LEOPOLD'S"
  3. 1 2 3 Crosby, "PENNYWHISTLE MODEM"
  4. ↑ Steven Levy, "Hackers", O'Reilly Media, 2010, pg. 220
  5. ↑ Les Solomon, "Solomon's History", InfoWorld, 15 Oct 1984, pg. 55
  6. ↑ William Hawkins, "Computer add-ons", Popular Science, May 1978, pg. 68
  7. ↑ See ComputerMart advertisement, InfoWorld. 31 March 1980, pg. 12

Bibliography

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