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Canon 161 Calculator

Updated 11/25/2005

The Canon 161 is an example of Canon Camera Company's (As Canon was known back then) first-generation of desktop electronic calculator. This machine is a direct descendent of Canon's first electronic calculator, the Canon 130, which was first shown in prototype form by Canon at a business machine exposition in Japan in May of 1964, and formally introduced in October of '64. Canon got into the electronic calculator business mostly out of necessity. Given that Canon's main business focus (excuse the pun) was optical instruments, Canon had a very great need for performing the complex math needed for design of increasingly complex optical systems. Back in the early 1960's when all this was going on, large scale computers were available for such calculations, but such machines very expensive, and weren't easily accessable to the engineers. What Canon needed was a device that could be put on an engineer's desk that would allow the engineer to do their own "back of the napkin" calculations needed for the design of optics. Existing electromechanical desktop calculators of the day were slow, noisy, and weren't capable of higher-level math functions without a lot of manual manipulation that could lead to errors. Canon had strong internal resources for design of electronics, and it was decided that perhaps Canon could "grow their own" electronic calculator to meet their engineers needs, and at the same time, open up a potentially lucrative new area of business for the company.

The Prominent "Brag Tag" on the Display Bezel

As early as 1962, Canon management had realized that there was a growing market for business machines, and in the five-year corporate plan created in that year, Canon executives decided that the company needed to make an entry into the business machines market. This business-driven need, along with Canon's own internal calculation need, combined to cause Canon management to create a group tasked with designing a practical desktop calculator. By early 1964, the calculator group had succeeded in building a prototype of a desktop-sized, four function, all-transistor electronic calculator that could serve the needs of Canon's own engineers, as well as provide Canon a strong entry into the rapidly developing market for electronic calculators.

The Canon 130, Canon's First Electronic Calculator

That machine was dubbed the Canon 130. By October of 1964, Canon had put the 130 into volume production and built up a sales organization, and the machine hit the market, quickly proving that Canon Camera and Instrument Co. was indeed a player to be reckoned with in the newly created and rapidly expanding electronic calculator marketplace. Within the period of a year, Canon had introduced a number of other calculators based on this first generation design, including 161, the 'top of the line' of the first generation of Canon calculators, and the 151, essentially a 15-digit version of the 161.

The Model/Serial Tag Located on the back Panel of the Cabinet

The Canon 161 exhibited here is a follow-on to that original Canon 130 design. The 161 uses all of the same technology and architecture as the original 130, including the very unique Canon-designed display subsystem. The 161 differs from the original 130 by virtue of 16 digits of capacity versus the 13 digits of the original machine, and adds a single memory accumulator register that wasn't present in the 130. The 161 was introduced in November of '65, meaning that this particular 161 is fairly late example, being produced sometime in the late 1967 timeframe, based on date codes stamped onto the circuit boards.

Canon's Unique Electro-Optical Display

The most striking thing about the first-generation Canon calculators, apart from the sheer size of the machines, is their display. The displays used on these machines are a completely unique display technology devised by the optical wizards at Canon expressly for use in their calculator. The display is an electro- optical design, relying on incandescent lamps to side-light thin panels of clear plastic that have fully-formed numerals and symbols (such as the decimal point) engraved into them as a series of tiny dots. These panels are stacked one atop another, much like the individual digit electrodes in a Nixie tube.

Display Module Construction
Module Front
Module Back (minus rear cover)
Metal Lamp Block
Lamp Circuit Board
Digit Panel Assembly
Individual Digit Panels

Each digit panel has a tiny incandescent lamp associated with it that lights when that the numeral on the panel is to be displayed. When the tiny lamp corresponding to a given digit panel lights, the light is injected into the edge of the plastic panel. The engraved area in the plastic causes interference with the light as it travels through the plastic, and some light is refracted out through the plane of the panel, causing the engraved dots making up the digit to light up with a white glow. The resulting digits look much like the fully formed numerals in a Nixie tube, except rather than an orange glow, the Canon display digits give off a cool white glow like that of an incandescent light bulb.

Digit Grouping Bars

Each display element contains twelve of these plastic panels with the digits zero through nine, a right-hand decimal point, and a vertical bar situated to the right of the digit that is used both for grouping results into groups of three for easier reading, and for separating the multiplicand and the multiplier when doing multiplication problems. The vertical bar lights up green (a result of a green coating on the edge of the panel that the bar is engraved in) to make it contrast against the white digits and decimal points. The calculator doesn't perform any leading or trailing zero suppression, which seems somewhat of an omission on a machine with not easily replaced incandescent lamp-based display technology. It seems that suppressing display of unnecessary zeroes would have extended the life of the tiny lamps that light up the digits.

Profile View of the Canon 161

Part of the reason for the physical size of the machine is that the display technology Canon used simply was not fast enough to allow multiplexing the display. Multiplexing significantly reduces the amount of circuitry necessary to drive a display, by time sharing the circuitry that translates the internal representation of the numbers into the form needed by the display devices, as well as the drive circuitry for the display. In order for multiplexing to work, the display elements must have the ability to turn on and off quickly, as the display is actually scanned a digit at a time, done at a fast enough rate that the human eye sees the display as continuously on. The tiny incandescent grain of wheat lamps used in the displays simply can't respond fast enough to allow multiplexing to occur at a fast enough rate such that the human operator wouldn't notice an annoying flicker as the digits are scanned. As a result of this, the circuitry to drive the display in the first-generation Canon calculators with this display technology is much more complex, with individual digit decoding and driving for each of the sixteen digits in the display panel. While complex, such a display technology is more straightforward to design, which may explain why some other early calculators such as the Wang LOCI-2 and Sharp Compet 20 use a similar "decoder/driver per digit" design.

Canon 161 with Cabinet Removed

The electronics of the Canon 161 are quite conventional, using basic diode/transistor gates for logic functions, and flip flops for bistable elements. One aspect of the Canon machine versus other machines of similar vintage is that Canon opted to build all the working registers of the machine out of flip flops. This results in a greatly increased parts count as compared to competitors designs that used acoustic delay lines or magnetic core memory to store working registers. The machine uses a fairly standard Binary-Coded Decimal architecture, with each register made up of shift registers which circulate through a serial arithmetic unit. When calculations occur, the digits shift through the arithmetic unit and are operated upon, with the results shifted back into the appropriate register.

Two of the 161's Circuit Boards (each containing part of the accumulator)

The brains of the machine are distributed across eleven circuit boards, each measuring about 12" x 9". The boards plug into a hand-wired (and beautifully so) backplane, with two edge connectors on each card. The backplane is situated on the left side of the card cage, so the cards plug in horizontally. Some cards also have an edge connector on their top edges, mostly for the myriad connections to the display assembly. The circuit boards are made of phenolic, and have circuit traces only on the back side. The wire side of the board is coated with a greenish-tinted resist. Wire jumpers on the component side of the boards are used in cases where the traces on the back simply can't get from point A to point B. The circuit board layout is quite conservative, with fairly low component density. The boards appear to have been laid out more for easy circuit routing than optimizing density. Oddly, given the apparent lack of concern for ease of service from a mechanical perspective, the signal names of each of the backplane signals are clearly marked at the edge connector pins of each circuit board. Apparently the electronics designers were more service conscious than the mechanical engineers.

Topside Wiring Harness (Mostly connections to the Display)

Mechanically, the 161 is built nicely, with high quality heavy-gauge sheetmetal stampings and quality fasteners. The cabinet is a complex sheet metal affair, that is quite heavy, and probably close to bulletproof! The keyboard and display bezels are easily removable, retained by posts that engage in friction retainers. These bezels simply pull off, and then the two screws that hold the cabinet in place can be removed, and the cabinet carefully lifted off. Even though the machine is very sturdy, it's clear that the machine was not really designed for serviceability from a mechanical perspective. Examples of a lack of thinking of the serviceability of the machine are numerous, including a card cage that is situated such that its impossible to pull out a circuit board without first removing the entire card cage from the baseplate of the machine! Another example of this is the display subsystem -- the display elements are all hard-wired, meaning that replacement of an individual digit unit would require unsoldering 13 wires in order to get the defective unit out of the chassis, followed by resoldering all 13 wires back onto the replacement unit. It also appears that the display modules themselves are not serviceable, meaning that when a lamp burns out, the numeral associated with that lamp will not light. While Canon's display technology was innovative, the longevity of the incandescent lamps surely wasn't as good as other display technologies (such as Nixie tubes) that were available at the time.

The Power Supply Circuitry of the Canon 161

The card cage takes up most of the real estate inside the back part of the machine. The front area of the machine contains the display subsystem, the power supply, and the keyboard assembly. The power supply is very straightforward, with a large transformer converting AC line voltage to lower-voltage AC, diode rectifier bridges converting the lower voltage AC to DC, large capacitive filters smoothing the ripple, and transistorized regulators keeping the voltages consistent. Amidst the power supply is a small fan that pulls air through vents in the bottom plate of the machine and directs it upward through the electronics and out vents in the side and upper surfaces of the cabinet.

Detail of the Keyboard's Workings

The keyboard assembly is made of a beefy plastic chassis. The keystalks penetrate the chassis to actuate leaf switches that close when the key is depressed. A spring situated under each keycap provides a positive return for the key when the key is released. The power switch and the memory accumulator control switch are the only two switches that don't use this leaf switch configuration. The keyboard connects into the electronics via a meticulously bundled cable.

Detail of the Canon 161's Keyboard

Functionally, the 161 provides addition, subtraction, multiplication, and division, along with a memory accumulator. Addition and subtraction are performed using the two [=] keys, one black for addition, and the other, red, for subtraction. Multiplication problems are entered as expected, by entering the first number, pressing the [X] key, entering the second number, then pressing the black [=] key to calculate the result. However, when entering multiplication problems, the display is unusual, with both the multiplicand and multiplier on the display at the same time. This method of multiplication display is used on a couple of other calculators in the museum, including the Sharp Compet 20 and Brother Calther 412. The 161 uses a green-colored bar to separate the multiplicand from the multiplier on the display. For example, performing 123 X 456 would end up showing up on the display as "0000000000123|456.", with the vertical bar indicating the multiplication. A factor complicating this is that the machine can't display multiple decimal points on the display at once (the decimal point logic is a '1 of 16' decoder), so performing multiplications with numbers that contain decimals can look rather odd on the display. For example, performing "123.456 X 456.78" would display as "00000123.456|45678". The correct answer is given when the [=] key is pressed, but the decimal point location on the display only reflects that of the first use of the decimal point key. The machine keeps track of the location of the multiplier's decimal point internally without displaying it. Division works conventionally, with the black [=] key displaying the result. One unusual feature of the machine that took a bit to figure out is the [R] key. My assumption was that it was a "reverse order" key, used to swap the operands in division problems. This feature is very common on later Canon calculators (though it is usually labeled "RV"), so I figured that this was the case on the 161 also, but in tinkering with the key, it was clear that this key did not perform that function. After a lot of experimentation, I found that this key displays the remainder after a division is performed. Why this feature was included isn't clear, but it is most certainly unusual. The 161 has no notion of negative numbers, results "below zero" simply wrap back around to 9999999999999999. For example, performing 10 - 20 results in 9999999999999990. An additional press of the [=] key will perform a 10's compliment operation, which, in the case of the example, would result in 10 being displayed.

Backplane Wiring

The 161 provides a full floating decimal point, but the functionality appears not to be complete in its implementation, especially with regard to addition and subtraction. Any time there are digits behind the decimal with addition and subtraction problems, all entries must contain the same number of digits behind the decimal point, or the result will not be correct. The machine does not appear to align decimal points before adding/subtracting. This could be the result of a problem with the electronics of the machine, or could have been a design compromise. It's hard to tell without a manual for the machine. The calculator operates perfectly otherwise, which leads me to believe that this anomaly is more a design compromise rather than a fault with the machine.

The 161 provides a memory register which serves as an accumulator. It appears, at least in early production Canon 161 calculators, that the memory add and subtract keys were not included, and somewhere along the production process, the ability to directly add or subtract the number in the display to/from the memory register was added. A fellow calculator collector has a Canon 161 with a significantly earlier serial number, and it lacks the memory add and subtract keys. Also, an advertisement in a publication dated October of 1967 also shows the 161 without these memory function keys.

Late 1967 photo of final assembly & test stations for Canon 161 at Canon's Shimomaruko factory

The memory register acts as an accumulator, with separate keys for adding or subtracting the content of the display from the accumulator (white [M] and [M] keys). The memory register is cleared with the [CM] key, and recalled to the display via the [T] key. A push-on/push-off key labeled [A] causes automatic accumulation of products or quotients into the memory register when activated, a useful feature for performing sum of product operations. On early 161's without the white and red [M] keys, this [A] mode key was the only way to accumulate numbers in the memory register.

Rounding out the keyboard functions, the [C] key clears the entire machine, including the memory register. This key must be used after powering the machine up, as when it is first powered on, the display contains random garbage (apparently there is no power on clear) and will behave strangely until cleared with the [C] key. The [CI] (Clear Indicator) key clears the display (but not the memory register), but only after a calculation has been performed, making the key useless as a "clear entry" function for correcting entry mistakes. The [→] key performs two functions. First, it can be used to position a number of the display by shifting it to the right. This can be used to trim off trailing insignificant digits, truncating any result to a user-desired number of digits. An example of the use of this would be to trim the result of a division down two a few significant digits, such as if the user performed 1/3, and wanted the result only to three decimal places. The machine would provide "000.3333333333333" as the result for 1/3. Pressing the [→] key ten times would shift the least-significant digits off the display, resulting on '0000000000000.333' when done. The [→] key can also be used to correct numeric entry errors, by "backing out" entered numbers a digit at a time for each depression of the key.

Red "Input Overflow" Indicator on Display Panel

The 161 has an overflow indicator on the display panel, consisting of a small incandescent bulb located behind a red jewel. This overflow indicates input overflow only, however. Mathematical overflow is not detected by the machine -- any result which exceeds the capacity of the machine simply "rolls over" with no warning, which means that the user must be vigilant when working with large numbers that could result in overflows.

The 161 is not a fast calculator, but given its vintage, it was a major improvement over the earlier mechanical and electro-mechanical calculators that it was designed to replace. Addition and subtraction complete in just a blink of an eye. Multiplication and division times vary depending on the complexity of the calculation. Simple multiplications take perhaps a few 10's of milliseconds. 99999999 X 99999999 takes nearly a second to perform. The machine can't deal with the 'all nines' division benchmark to its full capacity due to limitations of the logic of the machine. When dividing, the dividend is shifted to the left end of the display once the divide key is pressed, and apparently the logic that performs this shifting can't deal with a dividend greater than 13 digits in length. Entering a dividend with more than 13 digits causes an input overflow to occur when the [÷] key is pressed. Performing 9999999999999 (13 nines) divided by 1 takes about 1 1/4 second to perform. It appears that during calculations, the displays are dimmed, by perhaps lowering the lamp driver voltages. Even though the displays dim during calculation, it is possible to observe (though the incandescent lamps used in the display are far too slow to keep up with the rate at which the machine is churning through the calculation) some "spinning" of the digits and the decimal point racing around. As with most early electronic calculators, division by zero throws the machine into fits. An unusual quirk of this machine, however, is that the machine can't deal with zero as the dividend, as well as a divisor. Apparently the logic that shifts the divisor over to the left end of the accumulator looks for a significant digit (one through nine) in the most significant digit to signal the logic to stop shifting, and when the divisor is zero, there's no signal to stop shifting...so the machine gets hung in a loop trying to position the divisor. While this is going on, you can see the decimal points flitting right to left, then wrapping back around to the right as the never-ending shifting continues. Pressing the [C] key stops the madness and returns the machine to a sane state.


Special thanks to Donald Dupre for the opportunity to acquire this amazing artifact.


Text and images Copyright ©1997-2011, Rick Bensene.