Electronic Design
A Quick Blast from the Past

A Quick Blast from the Past

Handheld or pocket calculators, breaking into consumer markets in the early 1970s, are probably the earliest examples of products with mobile displays.

Portable televisions also were making the scene around the same time. But early portable TVs used CRTs, and portable meant they could be carried to another room with an ac-power outlet. Batteries weren’t a common option.

The no-frills pocket calculators of the day, responsible for permanently retiring the slide ruler, initially featured a vacuum fluorescent display (VFD) and, later on, basic seven-segment LED displays (Fig. 1).

Though smaller and more power-efficient than earlier versions, these LED-segment displays are still in use today, again in calculators and a wide range of other low-cost products such as alarm clocks, basic appliance displays, and meters.

One early example, circa 1973, the Casio CM-603A employs a blue, six-digit NEC LD8084 VFD (Fig. 2). The calculator includes a display shift key that enables the VFD to display up to 12 digits. A paperweight by today’s standards, the calculator measures 153 by 81 by 37 mm and weighs 236 g without its carrying belt and the four AA batteries it requires.

Notably, the power and display-driver circuit consists of only six transistors, six diodes, 14 capacitors and resistors, and a transformer (Fig. 3). Again, that’s a lot compared to current designs, but not too shabby for the day.

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