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Friden EC-130 Electronic Calculator


This exhibit is dedicated in perpetuity to Robert "Bob" Ragen, chief architect of the EC-130 calculator [7/23/1928-7/20/2012]

Updated 6/18/2014


This is a truly wonderful and historical machine. It is one of the earliest all-electronic desktop calculators, and is generally regarded as the first solid-state transistorized electronic calculator, although there is evidence that Sharp (Compet 10) and IME (IME 84) actually introduced their first electronic calculator just days before Friden did. Earlier electronic calculators used relays or gas-discharge tubes, such as the Casio 14-A relay calculator (1956), or the thyratron tube-based Sumlock Comptometer/Bell Punch Anita C/VIII (1961). The Friden 130 pioneered the use of Reverse Polish Notation (RPN), a method of entering math problems using a multi-register stack. RPN logic made complex calculations easier to perform without having to write down intermediate results and re-enter them into the calculator when needed. Friden continued the use of this stack-based method of calculating in its second generation of calculators (an example being the Friden 1162), but for some reason the principle was never patented by Friden. The use of the RPN methology applied to electronic calculators was originally patented by Mathatronics, in their Mathatron calculators, which hid the RPN implementation from the user, but used it internally to carry out the mathematical operations. Later, when Mathatronics was liquidated after being purchased by Barry Wright Corp., Hewlett Packard purchased the rights to the patent, as a means to protect their use of the RPN method in their first electronic calculator, the HP 9100A. HP's use of RPN proved so successful that HP still uses it on many of their calculators to this day. Later calculators from Singer/Friden (111x-Series and beyond) abandoned RPN in favor of more conventional arithmetic logic.

The story behind the development of the Friden 130 is somewhat shrouded in the mists of time, but it appears to be that Friden management realized that the days of the electro-mechanical calculator were numbered sometime in 1960, after hearing of work involving the development of an all-electronic calculator in Britain. The implication that electronics could take the place of the intricate mechanical machines was huge, and potentially threatening to Friden's market leadership position. Friden management wanted no chance that thier bread and butter business could be threatened. Something had to be done quickly to assure that Friden would enter the electronic calculator marketplace.

In 1961, Sumlock Comptometer, Ltd., set the calculator world on end when it introduced the first commercially available electronic calculator. The Anita Mark 7 and Mark 8 calculators caused many makers of electro-mechanical and relay calculators to realize that the future of calculating was with electronics. Electronic circuitry is fast, quiet, and reliable. Electro-mechanical calculators were noisy, slow, and had lots of moving parts that required regular maintenance to continue to operate properly. Relay calculators, while less noisy, and faster than electro-mechanical machines, also had moving parts (relays rely on mechanical movement to close switch contacts), and also had myriad switch contacts that wore over time and required periodic maintenance and adjustment. On top of this, relays take up a lot of space, use a lot of power, and are relatively expensive. The problem for the companies that sold electro-mechnical or relay calculators as their bread-and-butter business was that while they had brilliant mechanical and switching engineers, they had little in the way of the electronic engineering talent needed to design a practical electronic calculator. Most of the electronics engineers were working in military, space, aviation, computer, or communications technology, and those markets snatched up all of the electronic engineers as soon as they graduated from college. This led to a shortage of electronic engineers, especially those who knew anything about solid-state (transistorized) design, making folks with these talents a rare find in the early 1960's.

Robert Ragen, 1988
Image Courtesy of Dick Ahrens

By researching patent information, along with some first-hand information from a number of former Friden employees of the time, it has become clear that the essential contributor to the architecture and design of the Friden EC-130 was a brilliant electronic engineer named Robert Ragen. Ragen worked for Friden prior to the development of the Friden 130 on government-related electronics projects that Friden was involved in. The word is that the work involved secret electronic communications systems development (Data Encryption) for the National Security Agency. Those who would know details about this work, even to this day, are not forthcoming with information relating to the government projects, so one can assume that whatever the work was, it was and is still deemed critical to the defense and security of the United States. Whatever it was, it did provide Friden with some of the electronic stepping stones on the path towards developing a fully-electronic calculating machine to take over in place of the mechanical masterpieces that Friden was so famous for.

Friden also had some other in-house electronics expertise that had been acquired through the acquisition of a calculating-related product from Benson-Lehner Corporation. This machine integrated a modified Friden electromechnical calculator (Model STW-10) with a solenoid-activated typewriter and a cabinet full of relay and stepper switch logic, to make an automatic billing machine that could perform invoicing and accounting work, driven by programs fed into the machine on punched paper tape. Friden called the machine the "Computyper", and began making refinements to the Benson-Lehner design, creating different versions of the Computyper with successively more features. While initially electro-mechanical machines, the Computyper work did help bring additional logic and switching theory expertise to the company.

Along with the experience gained with the Computyper, there was also work being done on development of Friden's own small electronic computer system, which eventually became the 6010 electonic computing system. The 6010 was a basic computer targeted at office applications such as billing, payroll, inventory, and other accounting-related business activities. This work was done mostly in parallel with the development of the EC-130, and expertise was shared between the projects.

During the early 1960's, Friden was advertising heavily to attract electrical engineers and technicians to acquire the resources needed for the electronics projects that the company needed to staff. All of the expertise gained from hiring bright engineers as they could be found, the secret electronics work for the government, the evolution of the Computyper, along with the early work on Friden's own computer, all provided the internal expertise necessary to attack the problem of developing an entirely solid-state electronic desktop calculator.

At around the time that the revelation that Friden must develop an electronic calculator, the secret work for the government began to wind down. This made available some of the resources that Friden needed to jump headlong into a project to develop an all-electronic replacement for their mechanical calculators. Friden's senior management designated Friden's VP of Research and Development, Mr. Larry Robison as the driver for the project. Robison had a lot of experience in the computer industry, having worked for Burroughs for quite some time prior to coming to Friden, and thus understood a lot about developing complex digital systems. Robison assigned Bob Ragen as the leader of the development team. Ragen quickly put together a team of other Friden engineers and craftsmen who were put to task of developing a prototype of the Friden electronic calculator.

Through all the efforts to leverage the skills needed to develop the electronic caluclator, one critical piece was missing. Friden had decided that as a result of using a stack architecture for the calculator, it was very important that the machine display the contents of the stack of registers simultaneously. Doing so with Nixie tubes (the predominant display technology of the time) would result in a huge display (four rows of thirteen digits plus sign) that would be very expensive, and make the machine much larger than desired. It was decided that some other form of display would be required. The thought was that a TV-like cathode ray tube display would be best to meet the display requirements. However, the skills to develop the complex mix of digital and analog technology to create such a display system did not exist within Friden, and the timeline was so tight that developing a team to tackle the problem simply wasn't plausible.

The lack of the skills necessary to create a display system for the calculator became a critical path for Friden's calculator development project. To address the issue, sometime in the early part of 1961, Robison reached out to the Stanford Research Institute Computer Research Laboratory for assistance in the development of an electronic display system utilizing a Cathode Ray Tube (CRT), which was to be used for the display in an all-electronic desk calculator that Friden was developing. Robison had dealt with SRI during his time at Burroughs, and knew that SRI had the engineering talent to make the display system a reality. SRI was given a list of specifications, and was asked to determine if it was feasable to develop such a system, and if so, draft a proposal outlining a project to deliver a design for the system, as well as creating a working prototype system. SRI determined that the project was indeed feasable, and agreed to take on the project at a cost of $75,000.

The proposal from SRI was developed by two engineers, Jack Bialik and Milt Adams. Their proposal was promptly accepted by Friden. Bialik was made the project leader. Friden's specifications stated that a display system based on a small 1 1/2" x 5" x 10" CRT that would support the display of four registers of 27 characters each. Friden had also specified that the construction of the display must be completely solid-state (using transistors) other than the high-voltage circuitry to drive the CRT, and the CRT tube itself. The system was also specified to be as cost-effective as possible, as well as consuming the minimum amount of physical space possible. Bialik assembled a team of four engineers (Dave Condon, Dale Masher, Don Ruder, Bill Stevens) along with himself, to create the display system prototype. The project went very smoothly, and in early 1962, a month ahead of the date in the proposal, three prototype systems were delivered to Friden. The prototype consisted of four plug-in circuit boards that contained all of the circuitry needed to drive the display including the high-voltage drive circuits. Along with the display prototype, a simple calculator simulator was developed to demonstrate the display system in operation. The project went so well that in June of 1962, SRI cut a check to Friden for $4,444.62 as a refund on the $75,000 payment that Friden had made for the project.

Friden's legal department felt that the display system was a concept that should be patented. The display system that Bialik and his team had developed had some significant innovation in its design which led to the system being much less complex (and thus less expensive to build) than display systems that had been developed in the past. In the span of less than two years, an agreement was made between SRI and Friden for the patent rights for the display system to be assigned to Friden. In late 1964, Bialik, who at the time was doing contract work for the US military in France, traveled to the US Embassy in Pasis to sign the affidavits of assignment to provide Friden with the patent rights for the display system. US Patent number 3430095 was filed in July of 1965, with Bialik, Dale Masher, and Bill Stevens as the inventors, and Friden Calculating Machine Co. as the assignee.

While SRI was working on the display system, engineers at Friden were busily working on the calculating electronics for the calculator. Sometime around mid-1962, a prototype calculator was completed, utilizing SRI's display system. The prototype consisted of electronics that fit in a box about the size of a small filing cabinet. Sitting on top of this box was a console that provided the user interface for the calculator, consisting of the keyboard and the CRT display system developed by SRI. This initial prototype utilized a magnetic drum (Bryant Model C-105) to both generate the master clock frequency for the calculator (via dedicated pre-recorded timing tracks), and to store the working registers. While useful for a prototype, a magnetic drum just isn't practical for a desktop calculator. It was large, power-hungry, somewhat noisy, and not well adapted to an environment where the calculator may need to be moved around (magnetic drums were shock sensitive, and could also be thrown out of alignment if moved while operating). Some other form of storage would need to be used in the actual product, as a number of calculator makers that opted to try rotating magnetic memory for storage in their calculators found, including Wyle Laboratories (Wyle WS-01) and Canon (Canola 167) would later find out.

Photo of the large-scale delay line-based prototype version of the EC-130 Calculator.
The calculator electronics are in the large lower chassis, with the keyboard and CRT display and its drive electronics in the smaller unit sitting on top.
Pictured are (left to right): Ken Steward(Lab Tech), Unknown(Lab Tech), Unknown, Dick Ahrens(Engineer), Unknown, Bob McDonald(Sr. Engineer), Carl Herendeen(Logic Designer).
If you know the identy of any of the unknown folks, please contact the museum.


Another view of the EC-130 large-scale prototype, with Robert Ragen in the foreground

The early prototype machine shown in the photos above replaced the magnetic drum with a megnetostrictive delay line, which was much less costly and not nearly as temperamental as the magnetic drum. These proof of concept prototype calculators were far from practical for sale, but it served to demonstrate the concept -- Friden had what it took to build an all-electronic calculator. This large-scale prototype had all of the functionality of the what would be the production calculator, including RPN logic, CRT display, magnetostrictive delay-line storage, and transistorized construction.

Diagram of the prototype predecessor to production Friden 130 (From US Patent #3546676)
Note similarities to the prototypes in the photos above

Once the large-scale delay-line based prototype was debugged and working reliably, the next task was to shrink the cabinet of components that made up the electronics of the machine down to a practical and usable desktop-sized unit. A couple of factors that contributed to making this job a little easier were that the electronics in the prototype were designed more for development than production. Components were not tightly packed, circuit boards had wiring only on one side, and interconnections were widely spaced. Another factor was that the prototype was hand-made, which generally makes for a less space-efficient design. After all, a prototype is made to show that a concept is workable -- the effort is placed on making the idea a reality, rather than trying to optimize it for manufacture. In a mass-produced calculator, the space between components can be dramatically reduced, circuit boards can have wiring on both sides, and interconnections can be made much more dense.

This is where another problem developed. Friden did not have much experience making the complex circuit boards that were required to reduce the machine down to a desktop package. Friden needed to be able to manufacture circuit boards with traces on both sides of the board. This means that there has to be a way to provide connections through the circuit board to allow circuitry and traces on one side of the board to connect to traces on the other side. Such connections are called feed-throughs. For the small and fairly simple circuit boards used in their electro-mechanical calculators and Computypers, Friden had set up a circuit board manufacturing facility using a rather unique machine to etch the circuit board traces. This technology worked nicely for the simple single-sided circuit boards needed in the electro-mechanical calculators and Computypers, as well as the developing electronic computer (size is not as much of an issue in a computer system), but the EC-130 needed much more complex circuit boards with wiring on both sides of the board. This presented a problem. When prototype boards with feed-through plated holes were put through the machine, they tended to short out the machine, making the boards. As it turned out, the etching machine was used to make the single-sided boards in the EC-130's power supply, but due to this problem, the logic boards of the calculator were farmed out to a specialty firm that had the necessary equipment to manufacture the calculators logic circuit boards.

Larry Kramer, Friden Chief Draftsman (right) and Dick Ahrens, Electronics Engineer(left) pouring over the (huge) master schematic for the Friden 130
Sincere thanks to Dick Ahrens for donation of the Original photo and negative to the Old Calculator Web Museum

In the early part of 1963, a prototype of the calculator, all packaged into a desktop-sized unit, was ready, and exhaustive testing was begun. A disturbing problem was found where the calculator would inexplicably and randomly deliver incorrect results. Intense efforts went into finding the problem, which was finally traced to the high voltage section of the electronics (related to driving the CRT display). High electrostatic charge levels would build up, causing discharges that would make the calculator malfunction intermittently. Given that these calculators were expected to deliver accurate results all of the time, such a problem was intolerable. This, and a few other issues, delayed the formal introduction of the EC-130 to the public by almost six months. This delay led to a number of other companies developing solid-state desktop electronic calculators to beat Friden to product introduction, including Hayakawa Electric (Sharp) in Japan, and IME in Italy.

The First Pre-Production Desktop Prototype Friden 130, August 1963
Click on image for a more detailed view
Original photo donated to the Old Calculator Web Museum through the generosity of Dick Ahrens

There is a funny story relating to the first power-up of the prototype calculator. This story was was related to the author by Dick Ahrens, one of the electronics engineers that was hired on by Friden in early 1963 to work on the electronic calculator project. The story goes that when it was time to power up the fully-integrated prototype for the first time, a joke would be played on Bob Ragen. Ken Steward, a senior electronics technician involved in the calculator project, hid a 20-foot length of plastic tubing stretching from his lab bench to the inside of the prototype calculator, such that the tubing was not readily visible. Ragen had hooked a Variac (a variable voltage transformer) to the prototype calculator, so that the line voltage could slowly be ramped up to full voltage, just in case there were any problems. The time came, and Ragen turned on the power switch on the calculator, then slowly started turning up the voltage on the Variac. At around the same time, Ken, who remained at his lab bench, blew a bunch of cigarette smoke into the tube, resulting in wisps of smoke coming out of the precious prototype calculator. Ragen went into a panic, and frantically turned down the variac, pulled the power cord for the calculator out of the Variac, pulled the Variac's power cord out of the wall, and then ran to the main circuit breaker panel for the lab and killed the power to he entire lab. Only then was the trick revealed to Ragen, who was decidedly not amused by the prank. The power to the lab was restored, the plastic tubing removed, and the process of powering up the calculator was redone, and this time, everything worked just fine. Ragen took quite some time to forgive the conspirators that had played this joke on him.

With the desktop prototype machine working, it was decided that the machine needed to be shown to a few industry and trade insiders to get an idea as to the reception for this amazing machine. At a rather secretive event, the Friden 130 prototype was shown to a specially-selected audience at a business machines exposition in June of 1963. Attendees were required to sign a non-disclosure agreement stating that they must keep what they see completely secret. The attendees were shown the machine in a suite, away from the main exhibition floor. The folks that saw the prototype were absolutely floored over the speed, silence, and capabilities of the machine. It was clear to Friden from this event that they had a winner on their hands. Now, the task at hand was to ramp up the manufacturing operation to begin cranking out the EC-130 in production quantities, build an initial stock of machines to meet early demand once the machine went on sale, and train up the service force to be able to provide repair services for the calcualtor.

The Friden EC-130 is formally introduced by Friden's VP of Domestic Sales, S.P. Simmons in May, 1964.

While there had been a number of low-key previews of pre-production versions of the EC-130 from it's initial private showing in spring of '63, the formal public introduction of the EC-130 did not occur until almost a year later, almost six months behind the original timeline for introduction. The delay was due to a number of nagging reliability issues with the calculator, as well as some difficulties getting the manufacturing processes all spun up. The formal public introduction of the EC-130 occurred at the famous Waldorf-Astoria Hotel in New York City. The presentation of the electronic calculator was presided over by Friden's Vice President of Domestic Sales, Mr. S. P. Simmons. Mr. Simmons, in his address to the huge audience, stated that the EC-130 "was a worthy product to lead the industry into the era of electronics". Little could he have guessed that Friden's machine would lead Friden to quickly become the leader in the electronic calculator industry. While this leadership was rather short-lived (the Japanese very quickly ended up taking over the vast majority of the electronic marketplace by the late 1960's), the EC-130 truly began the mainstream adoption of electronic calculators in business and scientific persuits as replacements for the noisy and slow electro-mechanical calculators that had made Friden famous and very successful in the first place. The Friden 130's introductory price was $2,150, making it a significant investment, as a high-end desktop electromechanical calculator (albeit much slower and noisier) could be bought for just about a quarter of that price.

The prototype and early production EC-130 calculators had decimal point settings of 0, 2, 5, 9, and 13 digits behind the decimal point. When the EC-130 went into primary production, the decimal point settings were changed for some (currently unknown) reason to 0, 2, 5, 7, and 13 digits behind the decimal. In November of 1964 (November 20), a service letter (Calculator Release 0024) was issued by Friden headquarters indicating that a special batch of decimal point setting switches was procured with the original selections of 0, 2, 5, 9 and 13 digits behind the decimal. This was due to a significant number of requests from purchasers of early EC-130's that had noted the change, and wanted their machine to match the decimal point selections speficied when they ordered the machine. Friden offered installing the replacement switch in the field at a cost of $45.00 to the customer to satisfy these requests.

Early Friden 130 Marketing Trinket - Friden 130 Playing Cards
Donation of Original Item Courtesy of Dick Ahrens

As more and more EC-130's made it into the hands of customers, it became apparent that there were some teething pains with the product. Many of the early production Friden 130's had some fairly serious problems with reliability due to issues with the circuit boards. The firm that manufactured the circuit boards for Friden was having difficulty with the plated feed-through holes which provided connections from one side of the circuit board to the other. To fix this problem required tedious hand-soldering of feed-through connections in the field by Friden service technicians. Friden made good on these problems, providing highly skilled service technicians who spent a lot of time in training to be able to repair any faulty EC-130 quickly and efficiently. In fairly short order, the circuit board manufacturer solved the feed-through problems, and as the machines in the field that had the problems were repaired, the problems subsided. Even with some of the problems early-on, customers were delighted with this amazing machine that could quietly and very quickly solve their difficult mathematics problems.

An early prototype circuit board (unpopulated, used for flow-solder testing) from the Friden 130

Another early prototype circuit board from the Friden 130

Click on either image for more details.
Sincere thanks to Dick Ahrens for donation of these boards to the museum.

The architecture that Bob Ragen devised was very unique compared to designs of other calculating machines either prior-to, or after the 130. The 130 used an unusual arrangement of four (later, three) interconnected up or down counters (known as A, B, C, and D) and control circuitry, along with a novel way of storing data in the magnetostrictive delay line. The design was very elegant, minimizing the component count needed to implement the logic of the machine, and easily suited to the purpose of performing the basic four math functions. In the early 1960's when this machine was designed, transistors were still rather expensive. Minimizing the number of transistors meant that the cost to manufacture was lower than less-efficient designs, allowing more margin to be built into the final sales price of the product, while still providing a product that would be priced competitively in the marketplace. Ragen's design was quite a departure from the design of the Sumlock ANITA calculators, which at the time were the only other electronic calculators in the marketplace. The ANITA calculators were essentially electronic implementations of mechanical calculators. They operated in decimal, using ten-stage electronic counters much like the ten-step mechanical counters in rotary calculators. The Friden 130 uses a completely different approach, utilizing counters and trains of pulses stored in a magnetostrictive delay line to perform mathematical operations.

Block diagram of "Four Counter" Friden 130 Architecture
Click on Image for more detailed view

Sometime around mid-1965, it became apparent that one of the four counters (in particular, the B counter) in the machine could be removed, simplifying the machine and reducing the component count. Some redesign of the machine was necessary, but it was worth it to implement the change in order to reduce cost and improve reliability. Friden EC-130 calculators prior to serial number 8500 were "four counter" calculators, and from serial number 8500 and beyond, the "three counter" architecture was substituted. Friden service technicians had to be aware of this architectural change when servicing calculators in the field, as there were differences in circuit boards between the two designs of the 130. Along with being able to discriminate between the earlier four-counter and later three-counter EC-130s by serial number, it is also possible to know the architecture of the calculator without even looking at the serial number (located on the bottom of the calculator). The four-counter EC-130s displays the bottom-most register in the display in intensified form, while the three-counter machines do not have this feature. Originally, it was thought that intensifying the display of the bottom-most register (where all calculation results are displayed) would make it easier on the operator. The intensity was increased by actually displaying the bottom register twice during each display cycle. As part of the simplification of the logic involved in switching to the three-counter architecture, the feature was dropped. The machine exhibited here is a three-counter machine, indicated by its serial number of 12692, and also by the display (see image below), which does not have the bottom register intensified. Because of the parts cost reduction, as well as improvements in manufacturing processes, not to mention mounting competition from other calculator manufacturers (Sharp, Wang Laboratories, Casio, and IME), Friden reduced the price on the 130 to $1,695 effective July 27, 1965.

Inside the Friden 130

The Friden 130 uses diode-resistor "OR" and "AND" logic gates, with transistor-based inverter, buffer, and flip-flop devices. It performs math operations in bit-serial form, using the magnetostrictive delay line as the medium for storing its working registers. Logic levels are 0 Volts representing logic 1, and -12 Volts (nominally) representing logic 0. The delay line input transducer is driven with a pulse of approximately 20V, and by the time the signal makes it to the other end of the delay line, the voltage induced in the receiving transducer is approximately 35mV, or 35/1000th's of a volt. Digits are stored within the delay line as a series of pulses arranged in groups for each digit. Zero pulses represents a zero, and nine pulses represent a nine, with the numbers in-between represented by a number of pulses matching the number. As the pulses exit the delay line, they are amplified and fed into the counters (the A and/or D counters), which count the number of pulses in the digit to form a unique five-bit identifier that represents the number. The counter registers are not configured as counters in the usual binary sense. They are instead configured as five stage switch-tail shift registers, such that they count in a sequence of shifting 1's. For example; 0 is represented as 00000; 1 as 10000; 2 as 11000; 3 as 11100; 4 as 11110; 5 as 11111; with 6 as 01111, and ending with 9 as 00001. With five flip flops, each counter can represent the numbers zero through nine as unique combinations of bit patterns.

The delay line is a very interesting method of providing working storage registers for a calculator. Given that transistors were still rather expensive, some other means for storing the working registers of the calculator was needed. A little math shows how quickly the component count grows if the working registers of the calculator were to be implemented in circuitry. It takes at least two transistors to make a flip-flop, along with a complement of resistors, capacitors, and diodes. A flip-flop is essentially a 1-bit storage register. With 13 digits to store, and with each digit taking 5 bits, that means that there would have to be 65 flip flops, or a minimum of 130 transistors, to store one register in the stack. The 130 has 4 registers in the stack, plus one for the memory register. This would have taken over 600 transistors, along with hundreds of resistors, capacitors, and diodes, just to provide the storage for the registers. Such a design would have been prohibitive both in terms of cost and space required.

Ragen's solution to this problem was to leverage technology used in early computers (from the late 1940's through early '50's) to store the content of the working registers of the calculator. Before the advent of ferrite-core magnetic memory devices, one particular means of storage for electronic computers used long narrow tubes filled with Mercury with a transducer at each end. The bits of data took the form of sonic disturbances created by the transducer at one end of the tube. These disturbances propogated through the mercury at a fixed rate. The bits were sent through the mercury a bit at a time in serial fashion, and were constantly re-circulated through the tube like a big shift-register. When bits were needed, they were siphoned off by a transducer which converted the acoustical pulses to pulses of electrical energy, which were amplified and sent into the arithmetic unit bit at a time, where the appropriate operations were performed and the results pushed back into the bitstream circulating through the Mercury. The 130 uses a similar method, but rather than using exotic (and poisonous) materials like Mercury, a carefully-selected type of wire (made of a Nickel alloy) is used that holds the bits as tiny twists (torque variations) in the wire that move along the wire from one end to the other. The phenomenon is much like the wave that travels down a length of rope when you quickly whip one end of the rope. A transducer at one end of the wire places a twisting torque pulse on the wire which travels through the wire and is registered at the other end by a similar transducer. By continuously circulating these torque variations through the wire, the wire becomes the storage medium for the bits, and far less circuitry is required to maintain all of the bits that the machine needs to operate. In the Friden 130, the delay line takes the form of a large number of loops of this special wire, that, if unwound, would be about 50 feet in length. A pulse entering at one end of the wire will come out the other end in approximately 5 milliseconds, or stated otherwise, it takes about 5/1000ths of a second for a pulse to make its way from one end of the delay wire to the other. The wire is carefully strung in a series of spirals inside a sealed metal enclosure that takes up most of the bottom part of the chassis of the calculator.

A Closer View of the Card Cage

The circuitry of the three counter Friden 130 is contained on a total of seven circuit boards, each of which is about 12 by 5 inches. The boards, as expected, are packed quite densely with components. Most of the transistors are Germanuim (Silicon transistors were just becoming commonly available, and were significantly more expensive) junction transistors, mostly of the PNP type (predominantly 2N1305). The circuit boards plug into a backplane via edge connectors. However, the backplane connections weren't sufficient for all of the inter-board connections needed. Three groups of two boards each are wired together with many hand-soldered jumpers to provide the additional inter-board connections needed. The boards are put together in pairs of two, with wire jumpers connecting each pair of boards across the top edge of the boards.

The CRT, CRT Drive, and Power Supply Circuitry

Another small circuit board mounted to the aluminum chassis seperating the card cage from the CRT subsystem contains the drive circuitry for the CRT display, and a large circuit board situated underneath the CRT tube contains the power supply electronics, including a capacitor-diode voltage multiplier circuit that produces the high voltage (Approx. 2400 Volts) for the Westinghouse-made 5DEP1 electrostatic deflection CRT tube. The keyboard assembly also has a small circuit board with two transistors and a number of discrete components that provides signal conditioning for the keyboard outputs. The power supply provides 6.3V for the filament in the CRT, +6V and -12V DC as logic supplies, +80V for CRT deflection amps and delay line voltages, and approx. 2400V DC for the high voltage for the CRT.

A New-Old Stock (NOS) Westinghouse 5DEP1 CRT Tube, Circa 1967

The 130 has a 4-level RPN stack, with all four levels visible on the display. The content of the single store/recall memory register is not shown on the display. Digits are drawn in vector form on the display in a modified "pieces of eight" seven-segment form. Like all RPN-logic calculators, the Friden 130 has an [ENTER] key, which is used to enter the first number in an operation into the bottom register of the stack. A [REPEAT] key duplicates the number at the bottom of the stack by pushing the number in the bottom register in the stack up one, then duplicating it in the bottom register in the stack. This repeat function makes squaring much easier, allowing the user to calculate a square without having to re-enter the number (for example, 1232 would be entered as [1], [2], [3], [REPEAT], [X]). The [CHANGE SIGN] key toggles the sign of the number in the bottom of the stack. Numeric entry occurs in the bottom-most register of the stack. The standard four math keys perform their respective operations on the bottom two registers of the stack, with the stack shifted down after the operation is complete, and the result stored in the bottom-most register of the stack. When the stack is shifted down, the top-most register is set to zero. The [CLEAR ALL] key clears the stack, and the [CLEAR ENTRY] key clears the bottom register of the stack. The [STORE] key copies the bottom register of the stack into the memory register, clearing the bottom register of the stack. The [RECALL] key pushes the stack up, and copies the number in the memory register into the bottom register in the stack.

Friden 130 CRT Display

The machine handles 13 digit numbers, with thumbwheel-selectable fixed decimal point location. The keyboard uses a unique combination of electrical and mechanical construction. The keys actuate magnetic reed switches through a mechanical mechanism that encodes the keyboard keys into a binary code for the electronics. The keyboard is also mechanically interlocked by a mechanism controlled by the electronics. When an operation is performed, the function key locks down and isn't released until the operation is completed. This prevents the user from getting ahead of the machine. The keys are also mechanically interlocked so that it is impossible to press more than one key at a time. The machine performs only the basic add, subtract, multiply and divide operations, and has a single store/recall memory register. Shortly after the 130 was introduced, Friden announced a follow-on machine, the 132, which added a square-root function and provided more decimal point position selections.

Friden 130 Keyboard Layout (Click photo for detailed keyboard layout)

The 130 can take up to 2 seconds to perform difficult divisions, such as the "all-nines" (9999999999999) divided by 1 calculation. While this may seem a bit slow compared to what folks are used to today, this was orders of magnitude faster than the electro-mechanical calculators being used at the time, not to mention the fact that the 130 performed such operations with almost magical silence. The basic clock frequency of the four counter 130 is 666KHz (the clock rate was changed to 333Khz in the three register machine due to the elimination of one stage in the chain of divider flip-flops), which, for the time, is a relatively fast clock rate for Germanium-based transistor logic. The clock frequency is divided down by a chain of flip-flops that create the various master timing signals that orchestrate the operation of the calculator. During math operations, the display is blanked. If the machine is commanded to divide by zero, the display blanks and stays that way with the electronics running in a futile attempt to repeatedly subtract zero from the dividend. The OVER FLOW indicator does not light to show this condition as an error, which can lead one to wonder if the calculator has failed. Pressing the [OVER FLOW/LOCK] key, or the [CLEAR ALL] key stops the futility and returns the calculator to normal operation.

The [OVER FLOW/LOCK] Key Indicating an Overflow Condition

There is one additional key on the keboard which serves to unlock the machine in the event of overflow or an inadvertent division by zero. If the machine overflows, the keyboard locks, and an indicator in the [OVER FLOW/LOCK] key lights to indicate the overflow condition. Pressing the [OVER FLOW/LOCK] key clears the overflow condition (but not the stack), and unlocks the keyboard, allowing calculations to continue.

On June 24, 1965, an option for both the EC-130 and EC-132 calculators was announced to all Branch and Agency managers via Friden Inter-Office Communication C-0045. The option was desginated the 1901 Entry Counter, and involved adding a four-digit electro-mechanical counter to the calculator. The option was formally introduced to the public at the BEMA convention in New York in late October of 1965. A modification to the upper part of the cabinet was made to allow the counter to show through a cutout in the panel to the right of the CRT display. The counter would automatically increment each time a new numeric entry is made followed by the depression of any control key on the keyboard (with the exception of [CLEAR ALL], [CLEAR ENTRY] or [OVER FLOW/LOCK] keys). The counter could be cleared to zero by pressing a reset button on the counter itself. This option was primarily designed to make it easier for users to calculate averages, as well as for other calculations requiring a running count of items. The installation of this option could be made only at a Friden Service depot, at a cost of $75.00. The option could also be included on new calculators ordered with the option installed from the factory. The Friden 130 in the museum's posession has a cutout on the front part of the chassis for the counter to be mounted, as do the EC-132s, but none of the machines has the option installed. It is suspected that EC-130s built prior to the announcement of this option do not have the cutout in the chassis metalwork. The author is not aware of the existence of any EC-130 or EC-132 calculator with this option installed. If you have a machine with the entry counter option, please contact the curator.

The Romanian-made Felix CE-30
Image Courtesy Sergei Frolov

The Friden 130 apparently caught the attention of the Soviet Bloc. The above image is from a story in a Russian publication ("Radio" magazine) touting the latest in Communist technological innovations. The machine, called the Felix CE-30, was apparently to be manufactured in Romania. The photo is is virtually identical to the Friden 130, right down to the swoopy cabinet, keyboard design/layout, and CRT-display. In fact, it's so close (even duplicating the oval-shaped Friden logo to the left of the keyboard) that the unit pictured is likely a photo of an actual Friden 130, though at least the keycaps were either modified or airbrushed in with cyrillic nomenclature. It isn't clear if the machine was actually ever manufactured, but if imitation is the most sincere form of flattery, it sure seems that the Friden 130 was the benefit of some degree of admiration by the Soviets.

On a personal note, I saw and played with a Friden 130 when it was just introduced at the Pacific Science Center at the Seattle World's Fair site sometime in late '64 or early '65. (The World's fair was in 1962, and I visited it during that time, but the time where I saw the Friden 130 was during a later visit). Even though I was only around six or seven years old at the time, I very clearly remember this machine being there, and the feelings of amazement I had that this machine was able to quietly and quickly carry out all the math I could throw at it (which at the time wasn't much, but it was still fun to play with).

For some first-hand information about the Friden 130 and its follow-on machine, the 132, see the article entitled The Friden EC-130: The World's Second Electronic Desktop Calculator, by Nicholas Bodley. The article is a wonderful summary of recollections by Nicholas, who was a field service technician working for Friden at the time the Friden 130 was introduced. The article gives a fascinating look into the details of the development and workings of the machine. The article is used by permission.


Sincere thanks to Jack Bialik for his contribution of information relating to his development of the prototype CRT display system for the Friden calcualtor while he worked at SRI.

Text and images Copyright ©1997-2014, Rick Bensene.