Craig Model 4518

Kovac Corporation of Osaka, Japan, started already in 1972 with the Model K80 manufacturing of battery-operated electronic calculators. Most of Kovac's later products were sold not only under the Kovac brand, but made their way as OEM products into the distribution channels of Craig Electronics, Homeland, Prinztronic, Rambler, Unitrans, Ventron and others. Most of Kovac's calculators are based on Texas Instruments' early single-chip calculator circuits, the earliest designs used the TMS0105 chip. The Beetle series with their unique design was introduced in November 1973 and came in two sizes, small with five rows of keys and medium with six rows of keys. The smaller four- or five-function calculators were designed around chips from the TMS0800 Product Family while the more enhanced products made use of the TMS0600 Product Family.

This Craig Model 4511 is almost identical with the Kovac LE-808 calculator but has the CRAIG logo integrated into the mold of the display screen instead of using a simple adhesive sticker as found with the Prinztronic and other LE-808 derivatives.

Dismantling the featured Craig Model 4511 calculator manufactured in December 1973 in Japan reveals a very compact design with three different printed circuit boards (PCBs) cramped into the rather small package of the product. The Bowmar Optostic display needed some mechanical modifications before it was fixed with thermoformed posts into the calculator housing. Definitely not designed for repairs but availability for the Holiday Season 1973.

Calculating Unit: The TMS0801 located in the featured Craig Model 4511 calculator is a member of the TMS0800 Product Family and tracing back to the TMS1802NC, the first available standard calculator building block on a chip, later renamed into TMS0102. Soon after the introduction of the TMS0801, Texas Instruments added the TMS0803 with [%] function to the portfolio and many calculator manufacturer took advantage of its pin-compatibility and quickly introduced upgraded calculators. Think Bomwar MX20/MX25, Craig Model 4511/4511A or Kovac LE-808/LE-808P.

Display: This featured Craig Model 4511 calculator manufactured in December 1973 makes use of a mechanically modified Bowmar Optostic R7H-122-9 Nine-Digit display module using Chip-on-Board (COB) technology with each character formed by bonding seven individual Segment chips and one Comma chip bonded directly to a PCB and protected with a red plastic lens. The display module is connected with a 17 colorful wires to the Main-PCB.

Display Driver: The PCB of the Craig Model 4511 makes use of an unusual combination of one SN75491 Segment Driver and one SN75492 Digit Driver - inspecting the layout of the Main-PCB of the similar Craig Model 4518 used for the Characterization of the TMS0611 the reveals that the SN75491 Segment Driver was repurposed to act as a Digit Driver for three digits of the LED display while the SN75492 Digit Driver serves the other six digits. The calculator design utilizes the integrated Segment Drivers of the TMS0801 chip.

Clock: The Craig 4511 makes use of the internal clock oscillator of the TMS0800 chip, we identified a resistor with 100k Ohm connected between Pin 14 (R_EXT//Clock Select) of the TMS0801 and the V_DD power supply line, resulting in a clock frequency of about of 170 kHz.

Power Supply: The Craig 4511 is powered by a disposable 9 Volt battery and can be operated with an external, DC adapter, too. The Main-PCB of the calculator hosts a discrete power converter to generate the V_DD and V_GG supply voltages for the TMS0801 chip.

Keyboard: The Craig 4511 calculator makes use of a complex keyboard assembled with individual long-stroke push-button switches pushing conductive elements against small contacts etched into the Keyboard-PCB. The switches are arranged in an 10*2 matrix and are wired with short leads to the Main-PCB of the calculator.

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

© Joerg Woerner, December 25, 2024. No reprints without written permission.