DATAMATH

DATAMATH CALCULATOR MUSEUM

Sharp EL-204

Date of introduction:	October 1976	Display technology:	LED
New price:		Display size:	8
Size:	5.0" x 3.0" x 0.90" 128 x 75 x 23 mm³
Weight:	4.1 ounces, 117 grams	Serial No:	6311589Y
Batteries:	9V	Date of manufacture:	mth 12 year 1976
AC-Adapter:		Origin of manufacture:	Japan
Precision:	8	Integrated circuits:	TMS0956 (KGSΔ7642)
Memories:	1
Program steps:		Courtesy of:	Ken H. Meine
		Download manual:	(EU: 5.4M Bytes)

At first glance looks this early EL-204 calculator like a typical Sharp design of the Seventies but sports a red LED display instead the more common green Vacuum Fluorescent Display (VFD) known from many similar products of this timeframe.

Dismantling the featured EL-204 manufactured in December 1976 in Japan reveals a clean design based on a single-sided printed circuit board (PCB) for the main electronics and a double-sided PCB for the keyboard and powered by a disposable 9 Volts battery. Learn how to decipher the 6311589Y Date code hidden in the serial number of the pictured calculator.

Removing the PCBs from the calculator housing divulges an unexpected surprise! The EL-204 makes use of a Texas Instruments TMS0956 single-chip calculator circuit based on the TMS1000 Microcomputer family. The TMS0950 architecture was introduced in 1975 with the TI-1200 and TI-1250 and soon replaced with the TMS0970, one of the most successful calculator chip designs.

While the TI-1250 uses a 6x4 layout of the keyboard, changed the EL-204 the layout into a 5x5 matrix adding the sqr(X) function. Reverse-engineering of the EL-204 calculator demonstrates that the TMS0956 actually is scanning a 7x4 keyboard matrix, a previously unknown feature of the TMS0950 series.

The display module manufactured by Sharp of the EL-204 uses nine small LED chips bonded on a substrate with an additional magnifying lens to enlarge the digits.

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