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The Resilience of the Reed Relay

This simple electromechanical device, once crucial to telephone exchanges, lives on in portable defibrillators

1 min read
Vintage ad showing reed relays
Photo: Randi Klett

Invented in 1922 by a professor at Leningrad Electrotechnical University [pdf], the reed switch contains two slivers of wire that make contact in the presence of a magnet. Bell Telephone Laboratories evolved this device into the reed relay, in which the switch is controlled by an electromagnet. By the 1960s, reed relays were a fundamental component of telephone exchanges. Their ultralow power consumption also made them popular for space applications, including the Apollo missions.

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polaroid sx-70 camera, silver with brown leather, open on white surface
Thomas Backa

In one corner stood the defending champion, Texas Instruments. In the other stood the challenger, Fairchild Semiconductor. The referee, judge, promoter, and only spectator was Polaroid. In contention was the contract for the electronics of Polaroid’s secret project—a pioneering product introduced in 1972 as the SX-70, a camera eventually purchased by millions of people.

As the embodiment of truly automated instant photography, the SX-70 fulfilled a long-held dream of Edwin Land, founder of Polaroid Corp., Cambridge, Mass. Vital to this “point and shoot” capability was a new film—one that would develop while exposed to light and so eliminate the tear-away covers of previous Polaroid films. Also vital were sophisticated electronics to control all single lens reflex (SLR) camera functions, including flashbulb selection, exposure control, mirror positioning, start of print development, and ejection of print. These circuits were divided into three modules, one each for motor, exposure and logic, and flash control. At the final count, some 400 transistors were used.

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