Canon LE-83 (Display Version 1)

Canon introduced in January 1974 with the LE-83 their first calculator with an MSRP (Manufacturer's Suggested Retail Price) below $50. While we consider the LE-83 and its stablemates as members of the 4^th generation of Canon's product portfolio of Battery-powered Handheld Calculators with Light Emitting Diode (LED) display, does it reuse with the TMS0101 single-chip calculator circuit some technology of the 2^nd generation LE-80:

With the MSRP of the LE-80 in 1973 still around $100, Canon's engineering team needed to dig deep into the cost-reduction toolbox while designing the $50 LE-83 and it shows! Canon decided to use with the TMS0701 the 2^nd generation of the TMS0101 chip which allows to drive the segments of the LED display directly. Having the LED display in 1974 as the main cost driver of portable calculators, Canon opted for an 8-digit display and one additional discrete round LED for the minus sign instead the 9-digit display used with LE-80 but missed changing the code of the TMS0101. With the TMS0101 clearly developed for displays with a leading 9^th digit and Canon using just a discrete LED to the right of the 1^st digit instead a full character instead, the LE-83 expressed some strange behavior:

Canon's engineering team fixed this flaw with the LE-84 and LE-85 using two different approaches, consequently creating a rather divers portfolio:

Dismantling the featured Canon LE-83 manufactured in May 1974 by Canon in Japan reveals a rather compact design with three printed circuit boards (PCBs) for main electronics, display, and keyboard powered by four disposable Alkaline batteries. The Main-PCB is centered around a Texas Instruments single-chip calculator circuit and supported by a myriad of discrete components:

Calculating Unit: The LE-83 makes use of a 2^nd generation TMS0101 single-chip calculator circuit, also known as TMS0701 and derived from the TMS1802, better known as first "calculator-on-a-chip".

Display: Texas Instruments introduced together with the TMS0100 calculator chip two pre-configured LED (Light-Emitting-Diode) modules (DIS40, DIS95) based on the TIL360 arrays and the corresponding segment drivers (SN75491) and digit drivers (SN75492). Most early 8-digit designs like the LE-80 made use of these parts exhibiting two disadvantages:

Texas Instruments consequently introduced with the SN75493 and SN75494 revised display drivers optimized for designs with 3 or 4 batteries but the true innovation could be observed with the technology how to manufacture the 9-digit LED displays used with early four-function calculators:

On the tireless, never ending quest to squeeze the last penny out of the manufacturing costs of electronic calculators, Canon used with the LE-83 four different LED display manufacturers and technologies. With more than a dozen of LE-83, LE-84 and LE-85 calculators examined, we understood that Canon marked the backside of the 4^th Generation of Battery-powered Handheld Calculators accordingly, as of today we identified the following matrix:

Note: Here at the Datamath Calculator Museum we use a "Version Index" for the different display modules located in the Canon LE-83, LE-84 and LE-85 calculators based on the round paper stickers but couldn't find out the chronological order of them.

If your LE-83 uses resistors with a value of 2.2k Ohm instead of 5.6k Ohm as listed in the table above, your calculator was modified after April 1975 - Canon sent out a notice to their Service Partners to replace not only these resistors but even the digit driver transistors from 2N5449 to 2SC1641 in case the customers are complaining about a dim LED display. To better understand the influence of the digit driver transistors on the display brightness, we first measured the current gains (h_FE) of both transistors and two of the optional Transistor Arrays TA1 and TA2. In a next step we measured their Output Voltage vs Input Voltage transfer functions with an automated setup originally created for 75492-style devices. Here at the Datamath Calculator Museum we use this transfer function as an easy obtainable "Signature" of the underlying circuit design and manufacturing processes of digit drivers:

It is obvious that h_FE of the original 2N5449 BJT is on the lower side, meaning the digit drivers won't fully saturate with less than 1 mA base current and Canon consequently increased both base current with lowering the limiting resistor from 5.6k Ohm to 2.2k Ohm and increasing h_FE with changing the transistor type.

The featured LE-83 manufactured in May 1974 makes use of an ANTEX SK-3-307 8-Digit display module with eight 7-Segment displays chips bonded onto a Ceramic Substrate and magnified with a clear plastic lens. The display module is connected with 16 pins to the Main-PCB and follows the industry standard pinout of 9-Digit modules with the leftmost pin (Digit D9) unconnected. A small red LED with long leads is soldered directly onto the Main-PCB of the LE-83 calculator and bended over the display module to act as Minus "dot" for 8-digit numbers.

Display Driver: The Main-PCB of the featured LE-83 manufactured in May 1974 makes use of nine Transistors with supporting Resistors as discrete Digit Drivers for the LED display while the TMS0701 chip drives the Segments directly. The layout of the PCB would support two Transistor Arrays TA1 and TA2 with four, respective five transistors bonded and encapsulated into a small module, too.

Clock: While the nominal clock frequency of the TMS0700 single-chip calculator circuit is specified with 250 kHz, uses the LE-83 a much slower pace to reduce overall power consumption of the product slightly. The astable multivibrator using two discrete transistors operates at a frequency between 100 kHz and 150 kHz, we observed with the featured LE-83 manufactured in May 1974 a clock frequency of 132 kHz.

Power Supply: The LE-83 is powered by four disposable AA-sized 1.5 Volt batteries and can be operated with an external, DC adapter, too. The PCB of the calculator hosts a discrete power converter to generate the V_DD and V_GG supply voltages for the TMS0101 chip. To reduce power consumption of the calculator, the V_GG voltage is pulsed with the clock frequency between V_DD and its peak level. We observed with the featured calculator manufactured in May 1974 voltages of V_DD = -6.5 V and V_GG(pk) = -13.2 V while operated with V_BAT = 6.0 V. The LED displays of the LE-83 are operated directly from the battery voltage and we measured the current consumption of the featured calculator with:

The power consumption for the featured Canon LE-83 results in about 160 mW displaying a '0.' and 350 mW with all segments but the minus sign illuminated compared to the LE-84 (Display Version 1) sporting the same LED display with 100 mW and 320 mW, respectively.

Keyboard: The keyboard of the LE-83 uses spring-supported plastic keys pushing a small conductive rubber element against two contacts etched on a single-sided phenolic PCB combining both long-travel keys with reasonable manufacturing costs while maintaining longevity of the calculator. The keyboard module is connected with a short 18-pin flat-cable to the Main-PCB.

Here at the Datamath Calculator Museum we classify the featured LE-83 as Display Version 1.

The LE-83, LE-84, and LE-85 introduced in 1974 marked the last generation of calculators with LED displays in Canon's portfolio of Portable Handheld Calculators and the next product named LD-80 was sporting a green VFD (Vacuum-Fluorescent-Display) instead.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, December 5, 2001. No reprints without written permission.