Switch Tips: Display switches

June 17, 2004
Trends in ergonomics have led switchmakers to develop pushbutton switches that can also display short messages for the operator. These devices typically employ an LCD as part of the switch itself. The LCD is programmable.

Besides depicting operator messages such as On or Off, it can also be programmed to show simple images, animated graphics, and so forth, that aid in clarifying system status or spell out actions the operator can take.

Programmable switches of this nature consist of two distinct sections. The top section incorporates the LCD typically having a 24 X 36 dot-matrix display. The bottom hosts the switching functions. An LED provides backlighting for the switch display. Data that controls the display is clocked into the switch serially on one line. In all, just four lines are necessary to generate a switch display, and the same four lines can bus or daisy chain to several switches.

The LCD draws about 1 mA per switch. The LED backlight accounts for another 30 mA.

The bottom portion of the device includes switch contacts. The switch has momentary action and is normally open. Depressing the switch cap closes the switch contacts until the cap is released. The switch contacts are rated at 100 mA at 12 Vdc.

The display is controlled via a separate controller. The switch itself contains no memory; the controller handles all display refreshing. There are special controllers available to handle such switches, but ordinary microcontrollers can also handle the task. Switch makers provide software that lets developers create switch display bitmaps and specify which bitmaps display as a result of specific actions.Typical applications of these switches are in areas such as gaming, automated manufacturing equipment, military apparatus, and food-preparation appliances.

Information for this article was provided by NKK Switches, www.nkksmartswitch.com.

About the Author

Leland Teschler

Lee Teschler served as Editor-in-Chief of Machine Design until 2014. He holds a B.S. Engineering from the University of Michigan; a B.S. Electrical Engineering from the University of Michigan; and an MBA from Cleveland State University. Prior to joining Penton, Lee worked as a Communications design engineer for the U.S. Government.

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