Sharp EL-8117K

This Sharp EL-8117K caught our attention in 2023 while researching Texas Instruments' TMS1040 Product family of "single-chip calculator circuits" and we noticed that the TMS1042 was not exclusievely used in the beautiful Canon Palmtronic 8s and its siblings Palmtronic 8Rs and Palmtronic 8Ms. While Canon made use of the high integration of the TMS1040 chips and squeezed the electronics of a battery powered calculator in a very slim package of just 0.6" (15 mm) thickness, is this EL-8117K a rather traditional design of the Seventies.

Dismantling this Sharp EL-8117K manufactured in February 1977 in Korea reveals a very cost-optimized design using a single-sided printed circuit board (PCB) centered around a TMS1042 single-chip calculator circuit connected to a 9-digit Vacuum Fluorescent Display (VFD), a keyboard assembly and powered by 2 AA-sized alkaline batteries. Learn how to decipher the 78134362 Date code hidden in the serial number of the pictured calculator.

The TMS1042 is a member of the TMS1040 Product Family based on the TMS1070 "computer-on-a-chip" introduced in 1974 with the original TMS1000. While the TMS1070 can directly interface with low-voltage VFDs up to 35 Volts does it still need external resistors and a zener diode to bias the anodes and grids of the display with respect to the filament. The TMS1040 added an extra V_PP pin to connect a negative 30 Volts bias voltage for its modified output drivers. With the TMS1070 featuring 11 R Outputs for the Digits, 8 O Outputs for the Segments and 4 K Inputs for the Keyboard, reduced the TMS1040 the number of R Outputs to 9, consequently are all known TMS1040 calculator designs using a 9-digit VF Display.

Preparing our DCM-50A Platform to allow the Characterization of Single-Chip Calculator Circuits of the TMS1040 Family, we disassembled the featured EL-8117K calculator completely to trace its schematics and studied not only the timing of the keyboard scanning but the different implementations of the [^R_CM] and [^RC_RM] keys, too. While you need to press the button once to recall the memory of the EL-8117K and twice to clear it, uses the Canon LD-8Rs an implementation that recalls and clears the memory together.

Comparing the functionality of the three Canon Palmtronic 8 series calculator with this Sharp EL-8117K gives a good understanding of the programming of the TMS1042 software. Texas Instruments offered with most of their TMS1040 designs the calculator manufacturers a flexible menu to pick the desired functionality, meaning the chip would support both combined [C/CE] and [R/CM]/[RCM] keys or separate [C][CE] and [RM][CM] keys and the OEM would chose between them accordingly: