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Singer/Friden 1166 Desktop Calculator

Updated 7/15/2021

The Singer/Friden 1166 is a lower-cost and improved follow-on machine to Friden's 1160 calculator, with improvements made to make the calculator a bit more user-friendly. Along with the improvements for the user, the 1166 was also less-expensive than the 1160, due mainly to manufacturing efficiencies at the brand new Friden calculator factory in Albuquerque, New Mexico, as well as decreases in the cost of the integrated circuits used in the calculator. The 1166 was only built at the Albuquerque factory. The 1160 and 1162 were built at both the San Leandro and Albuquerque factories, once the Albuquerque factory was up and running in the summer of 1970.

The 1166 was the last of the 116x-Series of calculators made, and was also the last CRT-display calculator that Friden ever produced. After production of the 116x-series calculators ended, which appears to have occurred sometime in the late 1971 to early 1972 timeframe, all of Friden's calculators were designed and manufactured under OEM agreements with other calculator manufactures, most notably, Hitachi in Japan.

The Model/Serial Number Stamping on the Exhibited 1166

The exhibited Friden 1166 is likely a mid-production machine, with probably something on the order of 35,000 to 45,000 of the machines produced during the lifetime of the product. If you have a Friden 1166, and it has a serial number (which can be found on the bottom of the base of the calculator, as shown above) greater than 22927, please EMail the museum by clicking HERE and let us know the serial number of your calculator.

The Display on the Friden 1166
Note the lack of leading zeroes

The most obvious improvement from the 1160 is that the 1166 provides leading zero suppression. This feature eliminates all of the leading zeroes that clutter up the display on the 1160 (and 1162) calculators, making the display much more readable. Another considerable improvement with the 1166 is when entering numbers into the machine, the bottom line of the display actually shows the numbers exactly as entered, including the decimal point. The earlier 1160 and 1162 calculators would show the digits as they were entered, but the decimal point would not appear, requiring the operator to have faith that the decimal point actually was entered. The other aspect of this improvement in the 1166 is that decimal point entry was fully floating, meaning that the user could enter as many as nine digits behind the decimal point, regardless of the setting of the decimal point position thumb-wheel. If more than nine digits are entered after the decimal point, the extra digits are simply ignored. Even once the number is entered into the machine by pressing the [FIRST NUMBR/CHG SIGN] or using the [DUP] or [I] keys, the number will appear in the stack exactly as entered. The only time that the decimal point position selected by the thumb-wheel was taken into account is when a math operation was performed on the number(s), in which case, the result would be automatically rounded to the decimal point location selected on the decimal point position thumb-wheel, and any remaining digits discarded. This fully-floating decimal input and automatic roundoff feature made calculations with mixed decimal point positions significantly easier for the operator, as numbers could be entered exactly as they appear on the source document.

Along with the more obvious features of leading zero suppression, entry of numbers displayed exactly as entered, and fully-floating decimal point entry, another less-obvious feature was included in the 1166. This feature related to the top (fourth, invisible on the display) register of the stack. On the 1160/1162 calculators, when stack was popped (meaning an operation occurred on the bottom two registers of the stack, resulting in a single answer that causes the result to be placed in the bottom register, and the other three registers being copied down one level) the top register of the stack would be cleared after the operation completed. On the 1166, after a math operation, the number in the top register of the stack is copied to the third register, as well as remaining in the fourth register. As an example comparing the 1160 versus the 1166, consider the following content of the four-register RPN stack:

Top of Stack:      17.2345 Register 4
                 1600.7342 Register 3
    Invisible ↑ ---------- ↓ Displayed
                    3.1416 Register 2
                    1.4142 Entry/Register 1

The numbers below the dashed line represent the bottom two levels of the stack which are shown on the display. The numbers above the dashed line are the top two registers, which are part of the stack, but are not displayed. For this example, the display shows that the user has four numbers in the stack, with the last entry being 1.4142, shown in the bottom register of the stack. The decimal point position thumb-wheel is set to 4. Now, the user presses the [X] key to multiply the two bottom numbers in the stack (which are the two registers that are shown on the display). 3.1416 and 1.4142 would be multiplied together yielding 4.4429.

In the case of the Friden 1160 (in this example "display", leading zeroes are not shown for the sake of easier reading, though on the real 1160, they would be displayed), the bottom two numbers of the stack would be multiplied, and the stack would be popped downward, with the result of the multiplication then being placed in the bottom register of the stack:

Top of Stack:       0.0000 Register 4
                   17.2345 Register 3
    Invisible ↑ ---------- ↓ Displayed
               1 600.734 2 Register 2
                   4.442 9 Entry/Register 1 (Answer)

The pop operation would move the numbers down in the stack, with the answer replacing the 3.1416 that popped down to Register 1 after the multiplication occurred, with zero entering the top of the stack (Register 4).

Performing the same operation on the 1166 calculator, the resulting stack would instead look like:

Top of Stack:      17.2345 Register 4
                   17.2345 Register 3
    Invisible ↑ ---------- ↓ Displayed
                1 600.7342 Register 2
                    4.4429 Entry/Register 1 (Answer)

Note that the top register of the stack contains a copy of what was there before the multiply operation was carried out, and also that the number that was in the top register is also copied to the third register of the stack as a result of the pop operation. Also note that the 1166 does not group digits behind the decimal point in triplets, where the 1160/1162 does.

This Register 4 retaining feature can prove very useful when a constant is needed to be kept over a number of calculations. The constant can be pushed to the top of the stack using the [DUP] key (by pressing the [DUP] key three times). At that point the top three registers of the stack will contain the constant. Then a number can be entered, and an operation performed on it using the constant. This will cause the stack to pop, resulting in the constant in the top register of the stack to be popped down to the third level of the stack, as well as being re-entered into the top level of the stack, leaving the top three registers of the stack still containing the constant after the operation. For example, to calculate powers of two, one could press [2] [DUP] [DUP] [DUP] followed by repeated depressions of the [X] key to see successive powers of two with each press. If this operation were performed on the 1160 or 1162 calculators, the first three presses of the [X] key would yield a power of two because 2 would be in the top three levels of the stack, but after each press of the [X] key, a zero would be placed into the top register, and eventually would work its way into the top three registers of the stack, causing the next multiplication to be by zero, ending the power of two calculation.

The Friden 1166 Keyboard

The 1166 was developed primarily to decrease the price of entry for businesses into the realm of a modern electronic calculating machine. The updates from the 1160 were made to make the machine more attractive in an increasingly aggressive competitive market. The 1166's price at introduction was $895, $100 less than the 1160, making it not only attractive from a features standpoint, but also in terms of price. This price made the 1166 comparable in cost with many of the high-end electromechanical calculators of the time, and was very competitive with current electronic calculators with similar features from other manufacturers. The only sacrifice a buyer of the 1166 made over purchasing the more expensive 1160 was the loss of one digit of capacity, and a few decimal point settings, but the improvements in the user-friendliness of the 1166 more than made up for the sacrifice. The 1166 has a capacity of thirteen digits, and the decimal point setting thumb-wheel allows settings of zero through nine digits behind the decimal point, as opposed to the zero through eleven digits allowed on the 1160. The rotary switch for the decimal point setting has a physical stop at position 9 of the decimal point thumb-wheel, even though the thumb-wheel has labels for 10 and 11 digits behind the decimal.

It is likely that the reduction in capacity was done for marketing purposes, to provide extended marketability for the 1160 due to its additional digit of capacity, and not due to any real technical requirement. The additional digit of capacity that the 1160 provided over the 1166 could still be used to justify the purchase of an 1160 over the improved 1166 in situations where the extra digit of capacity might be needed. If the 1166 matched the 1160 in all aspects, as well as providing easier reading of the display, it would leave virtually no market for the 1160, likely resulting in the undesirable situation where there would be an inventory of un-sellable 1160's.

The delay line that stores the working registers of the 1166 is identical in specification to that used in the 1160 and 1162 calculators, meaning that other than minor changes to the cycling logic of the calculator, the 1166 could just as well have worked with 14 digits of capacity like the other two machines in the 116X-series.

The 1166 provides exactly the same keyboard functions as the 1160, with the standard four math operations, one-key sum-of-products [X=] function, and a single store/recall memory register. Other than the difference in capacity, display changes, and the fact that the top register of the stack gets a copy of the number that was in it after the stack is popped, the 1166 operates identically to the 1160. The display presentation, with leading zeroes suppressed and the entry register displaying the number exactly as entered by the user (including the decimal point), is visually much more attractive due to the lack of clutter caused by the leading zeroes that are displayed on the 1160/1162 calculators. The difference is very obvious when the 1160 and 1166 are operated side-by-side. The changes to the display on the 1166 make it much easier to read.

The Circuit Boards in the Friden 1166
Click on a board image for a larger view and more details about each circuit board

The 1166 shares the same type of small-scale integrated circuit devices used in the 1160/1162 calculators, with mostly DTL (Diode-Transistor Logic) devices, along with some TTL (Transistor-Transistor Logic) devices here and there on the circuit boards. The Texas Instruments-made custom counter chips (on Board #3) and NAND-gate ICs (on Board #1) used in the 1160/1162 are also used in the 1166. The exhibited 1166 uses one of the Friden R&D Lab-produced light-blue plastic-packaged "D Counter" Chips. These Friden made chips were initially developed by Friden's R&D Lab and made in limited quantities for Friden 115x and 116x-series production until Texas Instruments was up to full production capacity of the parts.

The Logic Circuit Board Backplane in the Friden 1166

The cabinetry, chassis, power supply, CRT driver circuitry, CRT, delay line amplifier board and delay line are identical to the earlier calculators. The keyboard is the same keyboard used in the 1160, even though it has different part number. The keyboard in the 1160 is interchangeable into the 1166, and vice-versa. The 1166 has five logic circuit boards, like the 1160. The only circuit board shared between the 1166 and the 1160/1162 is Board #1, the display generation circuit board. Architecturally, the 1166 is nearly identical to the 1160, with only logic changes to provide the leading zero suppression, one less digit of capacity, stack pop behavior, and fully floating decimal entry and display of numbers. From a mechanical standpoint, other than the differences in the backplane and nomenclature, the machine is identical to the Friden 1160.

Power Supply Voltage Regulation Pass Transistors and Power Resistors Mounted on Inside of Large Rear Heatsink Casting

The 1166 utilizes a total of 105 IC's, making it the most complex machine of the 116x-series calculators, though by the time this machine was manufactured, the price of the ICs used had gone down, especially the DTL ICs because they were quickly being replaced in new designs with TTL devices which had superior electrical characteristics. Along with the IC's, there is also a significant inventory of discrete components, though there are fewer discrete components in the 1166 compared to the 1160 and 1162 machines. The backplane board, which is unique to the 1166, contains most of the power supply circuitry, along with the interconnections between the sockets that the logic boards plug into. The back panel of the calculator is an aluminum casting, with heat radiating fins cast into it. On the inside of this panel are mounted four power-transistors that are involved in the regulation of the logic power supply voltages. The CRT deflection and blanking control board mounted beside the CRT is identical to that used in the 1160/1166. The CRT is the same 3WP1 tube, with 3-inch diameter display area and green medium-persistence phosphor. The delay line is functionally and visually identical to that used in the 1160 and 1162, but a slight change was made to reduce cost. Rather than the transducers at each end of the delay wire having two nickel-alloy magnetostrictive tapes welded to opposite sides of the circumference of the delay wire, the 1166 has only one tape connected at one side of the delay wire, at each end. It was found that one magnetostrictive element was sufficient to create a large enough torque twist on the delay wire to be able to be received by a single-tape transducer at the other end of the wire without requiring different write driver and read amplifier circuitry. This reduced the manufacturing time to manufacture the delay line, thus reducing its cost. The delay line timing (four millisecond delay) is the same as that of the 1160/1162, but it is not positively known if the delay lines are actually interchangeable between the 1166 and 1160/1162 machines.

Numbers are always entered into the bottom register (the bottom number on the display) of the stack. The [FIRST NUMBR/CHG SIGN] key is a dual function key. The first press enters a completed numeric entry into the bottom register of the stack, preparing the machine for entry of the next number. The number is entered into the machine exactly as it was keyed by the user, without any modification to fit the decimal point setting. For example, with the decimal point thumb-wheel set at 4, and the number 1.4142135 is entered, and the [FIRST NUMBR/CHG SIGN] key pressed, the number would show in the bottom register of the stack exactly as entered, e.g., 1.4142135, even though the decimal point position is set at 4. The number will also remain unmodified when it is pushed up the stack when another number is entered or the [DUP] key is pressed. The decimal point setting is only enforced once a math operation is performed, which is when the answer is automatically rounded off to the selected decimal point position. As with the 1160/1162, a successive press of the [FIRST NUMBR/CHG SIGN] key will toggle the sign of the entered number. The [DUP] key pushes the stack up, retaining the content of the bottom register of the stack. The [I] key swaps the content of the bottom two (the registers shown on the display) stack registers. The [TO MEMORY] button stores the content of the bottom register of the stack into the memory register (shifting the stack down), and the [FROM MEMORY] pushes the stack up, then copies the content of the memory register into the bottom of the stack. The [CLEAR] key pops the stack without duplicating the top number in the stack to Register 3, and clears the bottom register of the stack (allowing re-entry of incorrectly entered numbers), and also serves to clear the OVERFLOW indicator. The [CLEAR STACK] key clears all four registers of the stack, also clearing the OVERFLOW condition and unlocking the keyboard if it is locked, but does not disturb the memory register. The [X+] key operates like the [X] key, except that after the multiplication is completed, the product is automatically added to a running total which is maintained in stack Register 3 (not-displayed), with this register then copied to the bottom register in the stack after the addition is completed so that the running total is displayed. The 1166 display provides leading zero suppression, and also formats results ahead of the decimal point into three digit groupings for easier reading and transcription. There is a subtle difference in the three-digit grouping feature of the 1166 versus the 1160/1162 calculators. All digits ahead of and behind the decimal point are displayed in groups of three digits on the display of the 1160/1162. Only digits in front of the decimal are displayed in triplet groups on the 1166. The digit formation on the 1166 display is identical to that of the 1160/1162 calculators.

The Model Tag on the Friden 1166
Note Albuquerque, N.M. (New Mexico) Plant Identification

The "All 9's" divided by 1 calculation takes about 1/2 second, slightly faster than the 1160, mostly due to the fact that the 1166 has one less digit to deal with. Along with one fewer digit to operate on (as well as not having to wait as long for the registers in the stack to circulate through the delay line) there are some efficiencies gained in improvements to the logic that also slightly improve the speed of the machine as compared to the earlier machines. As with the 1160/1162, during calculation, the display is blanked, and the function key that initiated the operation is locked down by a solenoid mechanism in the keyboard until the operation is complete. Overflow lights the "OVERFLOW" indicator on the keyboard panel, and locks the keyboard until the overflow condition is cleared with the [CLEAR] or [CLEAR STACK] keys. Division by zero behavior is the same as with the 1160 and 1162 -- the machine loops forever with the display blanked and the keyboard locked, requiring depression of the [CLEAR STACK] key to restore the calculator to normal operation.

The ICE Felix CE33
Sincere thanks to Mr. Alex Floca for providing the photo of his ICE Felix CE33

Romanian company ICE Felix (Fabrica de Calculatoare Electronice FELIX) was created to market electronic calculators designed and manufactured by Friden, under license acquired from the Dutch division of Friden in the late 1960's. ICE Felix would purchase many of the mechanical parts of the calculators from the Friden factory in Nijmegen, Holland. Felix would fabricate its own Friden-equivalent circuit boards using native components, developed from Friden-provided design documentation. The parts would be assembled to create calculators that looked and functioned identically to their Friden-made equivalents. While the machines were manufactured primarily for sale in Romania and Hungary, some of the machines made it into Soviet countries, and were "cloned" and touted as pinnacles of Soviet technology. ICE Felix produced the Felix CE33 calculator, which was their version of the Friden 1166. Prior to the CE33, Felix produced their version of the Friden EC-130 calculator as the Felix CE30. These Romanian-made version of Friden electronic calculators are extraordinarily uncommon today.

Sadly, after the 116x-series calculators, Singer's management decided it was no longer viable to continue to design and manufacture electronic calculators in the United States. An agreement was made with Hitachi in Japan for Friden to market, sell, and service re-badged calculators designed and manufactured by Hitachi. Singer's management had been testing the waters with Hitachi as early as sometime in 1967, with Singer importing Hitachi's first electronic calculator, a transistorized Nixie tube-based machine called the ELCA 12, and re-badging the calculator, selling it as the Friden 1112. It appears that the Hitachi designed and manufactured calculators were good enough for Singer's management to decide to forge a formal OEM agreement with Hitachi sometime in late 1968 to early 1969. Once this agreement was in place, Singer also began phasing out Friden's calculator engineering and manufacturing operations. Singer's decision to outsource its calculator development and manufacturing put an end to the legacy of Carl Friden, and his creation of a company with his namesake that created calculating machines that were pinnacles of design elegance, reliability, and performance. By 1972, most all of the amazingly brilliant folks that were involved in the development of Friden's electronic calculators were gone, and it wasn't much longer after that, around the latter part of 1974, that Singer exited the calculator marketplace, putting an end to over 35 years of the Friden brand representing excellence in calculating machines.

Text and images Copyright ©1997-2023, Rick Bensene, The Old Calculator Museum.