Friden EC-130 Electronic Calculator

This is a truly wonderful machine. It is one of the earliest all-electronic calculators, and is generally regarded as the first transistorized electronic calculator. A few other calculator manufacturers in Europe and Japan claim that they were the first to develop an all-transistor calculator, but the simple fact is that Friden announced the Friden 130 nearly six months before these other manufacturers even displayed prototypes of their transistorized calculators. Earlier electronic calculators used relays or vacuum tubes, such as the Casio 14-A relay calculator (1956), or the tube-based Sumlock Comptometer/Bell Punch Anita C/VIII (1961). Along with being the first all-transistor calculator, 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. Later, Hewlett-Packard used RPN math logic in their first electronic calculator, the 9100A, and it proved so successful that HP still uses RPN logic on a good many of their calculators to this day. Later calculators from Singer/Friden 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 the general situation appears to be that Friden management realized that the days of the electro-mechanical calculator were numbered sometime in the early 1960's. Sumlock Comptometer, Ltd. had set the calculator world on end when it introduced the first electronic calculator in 1961, and many makers of electro-mechanical and relay calculators realized 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 which 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. The problem for the companies that sold electro-mechnical or relay calculators as their bread-and-butter business was that they had brilliant mechanical and switching engineers, but little in the way of the electronic engineers needed to design a practical electronic calculator. Most of the electrical engineers were working in military, space, aviation, or communications technology, and those markets sucked up all of the electronic engineers as soon as they graduated from college, making the good electronic engineers a rare commodity.

Robert Ragen, 1988
Image Courtesy of Dick Ahrens

By researching patent information, along with some first-hand information from a Friden service technician, Nicholas Bodley, it has become clear that the major contributor to the architecture and design of the Friden 130 was a brilliant electronic engineer named Robert Ragen. It isn't clear if Ragen was hired at Friden specifically to work on the electronic calculator project, or if he already worked for Friden as an electrical engineer for some of the more complex electro-mechanical calcualtors that Friden made. In any case, Ragen, along with team of other Friden engineers and craftsmen, came up with a prototype of the Friden electronic calculator whose electronics fit in a box just a shade bigger than today's small refrigerators. Sitting on top of this box was a console that provided the user interface for the calculator, consisting of the keyboard and CRT-display. This proof of concent was far from practical as a useful piece of office equipment, but it served to demonstrate the concept -- Friden had the means to build an all-electronic calculator. This prototype had all of the functionality of the Friden 130, including RPN logic, CRT display, acoustic delay-line storage, and transistorized construction.

Prototype Predecessor to Friden 130 (From US Patent #3546676)

Once the large-scale prototype was completed, 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 with very liberal design rules. 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. The problem was, Friden did not have much experience making complex circuit boards. In order to pack all of the electronics needed into a desktop package, Friden needed to be able to manufacture circuit boards with traces on both sides. 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 needed in their electro-mechanical calculators, Friden had set up a circuit board manufacturing facility using a rather unique means to etch the circuit board traces. This technology worked nicely for the simple single-sided circuit boards needed in the electro-mechanical calculators, but the 130 needed complex circuit boards with wiring on both sides of the board. This presented a problem. The feed-through holes tended to short out the machine that did the etching. Some methods were used in the manufacturing process to minimize this problem, but these methods created other problems that manifested themselves after the units were shipped to customers.

By late 1962, prototypes of the original design of the calculator were ready, and exhaustive testing was begun. A disturbing problem was found where the calculators 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. Efforts to identify, isolate and eliminate the problem resulted in the delay of the introduction of Friden's first electronic calculator for almost six months.

The First Pre-Production 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

By mid-1963, Friden had worked through the difficulties, and had a viable desktop (though it took up a substantial part of a normal desk top) calculator ready for market. Amidst some fanfare, an early Friden 130 prototype was shown at a business machines exposition in June of 1963. The interest was tremendous -- pre-booked orders started rolling in like hotcakes, even though the 130 was quite expensive compared to the electromechanical machines of the day, with an initial retail price of $2195. This was at a time where a desktop electro-mechanical calculator with about the same functionality could be purchased for around $500.

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

However, things weren't entirely rosy. As a result of some of the circuit board difficulties, early production Friden 130's had some fairly serious problems with reliability due to poor feed-through quality, which 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. Even with 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 Mr. 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 interconnected counters and control circuitry, along with a novel way of storing data in the acoustic delay line. The design was very elegant, minimizing the component count needed to implement the logic of the machine. 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 to sell in the marketplace. Ragen's design was also interesting from the point of view that it was quite a departure from the design of the Sumlock ANITA calculators - at the time, 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 binary counters and trains of pulses stored in an acoustic delay line to perform mathematical operations.

Inside the Friden 130

The Friden 130 uses diode-resistor and transistor logic gate technology. It performs math operations in bit-serial form, using the acoustic delay line as the medium for storing its working registers. 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 each digit taking 5 bits (the Friden machine used a rather unique 5-bit representation of each digit), 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' ended up taking 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 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 materials like mercury, a carefully-selected type of wire is used that holds the bits as slight 'twists' (torque variations) in the wire that move along the wire from one end to the other. The phenomena 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 torque pulse on the wire to create twists which are registered at the other end of the wire 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 number of loops of this special wire carefully strung inside an enclosure that takes up most of the bottom part of the chassis.

A Closer View of the Card Cage

The circuitry of the 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 more expensive) junction transistors, of the PNP type. 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 myriad hand-connected jumpers to provide the additional inter-board connections needed.

The CRT, CRT Drive, and Power Supply Circuitry

Another small circuit board mounted to the aluminum chassis separating the card cage from the CRT subsystem contains the drive circuitry for the CRT display, and lastly, 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 (3000 Volts) for the type 5DEP1 electrostatic deflection CRT tube.

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"). A "CHANGE SIGN" key toggles the sign of the number in the bottom of the stack. The standard four math keys perform their respective operations. The "CLEAR ALL" key clears the stack, and the "CLEAR ENTRY" key clears the bottom register of the stack. Lastly, 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 Model 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 9999999999999 divided by 1. 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. During math operations, the display is blanked. If the machine is commanded to divide by zero, the display blanks and stays that way...the electronics running in a futile attempt to repeatedly subtract zero from the dividend. 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