Canon LD-80 Panther D

Canon introduced in Fall 1974 with this Panther D its first Battery-powered Handheld Calculators with Vacuum-Fluorescent Displays (VFDs), putting an end to four generations of calculators using Light Emitting Diode (LED) displays:

Soon after the introduction of the LD-80 Panther D an almost identical calculator hit the shelves, replacing the "Canon PANTHER D" label above the display with a "Canon Palmtronic LD-80" label. Both calculators are using the same battery cover, reading "Canon MODEL LD-80". Despite using the same keyboard lettering are the internals of the two products completely different. While the original Panther D design is based on a Hitachi HD3633 single-chip calculator circuit, is the Palmtronic LD-80 centered around a Texas Instruments TMS0855 chip. Two completely different calculator brains in the same calculator created some interesting side effects for the user:

Two different calculator brains for the same calculator? Some former engineers at Lloyd's Electronics, Inc., Compton, California, are now smiling. Their Model ACCUMATIC 30 went through four (!) different single-chip calculator circuits and switched from an 8-digit VFD with discrete LED for the minus sign to a 9-digit VFD even before they changed the keyboard with the EH-9036-2 from 19 keys to 22 keys:

Dismantling this Canon LD-80 Panther D calculator manufactured in November 1974 in Japan reveals a clean design based on a single-sided printed circuit board (PCB) for the main electronics, a single-sided PCB for the keyboard and powered by four disposable 1.5 Volts batteries.

The Main-PCB is centered around a HD3633 single-chip calculator circuit manufactured by Hitachi and the few remaining components on the PCB are mainly used to generate the different supply voltages for the HD3633 and Vacuum Fluorescent Display (VFD) and to bias the anodes and grids of the display with respect to its filament.

On our quest to completely understand the differences between the LD-80 Panther D and Palmtronic LD-80 siblings, we decided here at the Datamath Calculator Museum to give both calculators a full "Teardown Treatment" and share our findings accordingly.

Calculating Unit: Hitachi started already in 1971 manufacturing with the HD3200-series Large-scale Integration (LSI) chips in P-channel Metal Oxide Semiconductor (PMOS) technology for electronic calculators. The first product based on the HD3200-series was the Singer/Friden EC-1117 Desktop Calculator using a total of nine LSI chips, not suitable for Battery-powered Handheld Calculators. Following Moore's Law, the observation that the number of transistors integrated into Integrated Circuits (ICs) doubles every 12 to 24 months, Hitachi was able to introduce with the HD3272 a 2-Chip design already in 1972 and the HD3633 introduced in 1974 seems to be the companies first single-chip calculator circuit. From a calculator developers point of view, the HD3633 is similar to other offerings like the TMS0855 used in the Canon Palmtronic LD-80 and features an integrated clock generator and segment and digit output drivers directly interfacing with low-voltage VFDs up to 35 Volts. An interesting design feature of the HD3633 is the separation between display scanning and keyboard scanning, allowing to scan only the actually used digits instead of always scanning the entire display and implementing the leading zero suppressing for the segments.

Display: The Canon LD-80 Panther D calculator manufactured in November 1974 makes use of a 9-Digit low-voltage VFD manufactured by Futaba and known as Type 9-ST-02A. The display is soldered with its 19 pins directly to the Main-PCB.

Display Driver: The term "low-voltage" Vacuum Fluorescent Display might be misleading when used together with a calculator powered by four 1.5 Volt batteries. Common VFDs used with portable electronic calculators are usually operated around 30 Volts, significantly higher than the 10 to 15 Volts operating voltage of single-chip calculator circuits used in the 1970s. The HD3633 single-chip calculator circuit is manufactured in PMOS technology, meaning its output transistors are "high-side" switching and the most positive voltage of the chip is labeled V_SS for 0 Volt, all other voltages in the calculator are consequently negative with respect to V_SS. Multiplexed low-voltage VFDs need a voltage difference between its filament and the grids and anodes of the numbers of around 30 Volts to light up and to avoid "ghosting" while scanning, the deactivated grids and anodes should be slightly lower than the filament voltage. Canon went with the LD-80 Panther D the traditional way and uses a power supply with multiple taps for the negative display voltages. The grids and anodes of the VFD are "pulled-down" with 17 resistors (100k Ohm) to around -30 Volts, the filament is biased to around -25 Volts and the HD3633 switches the relevant grids and anodes to around 0 Volt to lit them up.

Clock: The Canon LD-80 Panther D makes use of the internal clock oscillator of the HD3633 chip, we identified a capacitor with 180 pF connected between Pin 20 (CLKOUT) of the HD3633 and Pin 21 (CLKIN), resulting in a clock frequency of about of 75 kHz.

Power Supply: The Canon LD-80 Panther D calculator is powered with four disposable AA-sized 1.5 Volt batteries and uses a complex DC/DC converter module to generate a total of five voltages:

We measured the operating current of featured Canon LD-80 Panther D calculator:

Calculating the power consumption at 6 Volts for the Canon LD-80 Panther D results in about 180 mW displaying a '0.', about 280 mW with all segments but the minus sign illuminated. Not very impressive, a Canon LE-84 calculator using four disposable 1.5 Volt Alkaline batteries and a simple DC/DC converter for its TMS0801 chip clocks in at around 100 mW displaying a '0.' and 320 mW with all segments lit.

Keyboard: The keyboard assembly of the Canon LD-80 Panther D calculator makes use of a keyboard module with a single-sided phenolic-substrate PCB with gold-plated traces for the contacts and spring-loaded conductive rubber elements for its injection molded plastic keys. This technology used by Canon with many calculators form the early 1970s proved over time as very reliable. The keyboard PCB is connected with a short 14-pin flat-cable to the Main-PCB.

Don't miss the Panther 8.

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

© Joerg Woerner, September 20, 2003. No reprints without written permission.