Keyboards
CHOOSING ELECTROMECHANICAL INPUT SYSTEMS
In this article, Knitter-Switch’s CEO, Hans Peter Külb, helps buyers make the right purchasing choice by identifying the benefits of different keyboard technologies
Membrane keypad technology is frequently used in sports equipment and in vending machines. The user sees a plastic film, possibly with windows to accommodate displays, numeric displays or LEDs. This front graphic membrane is often embossed so users’ fingers are guided to the keys. Embossing options include: around key edges; raised keys and bubble-shaped. Embossing can also be used where Braille is required.
Graphic design possibilities are virtually unlimited. Keys of any
shape can be implemented at no extra cost and colours can be used for logos, corporate designs or optical layout.
Printing is always Knitter-Switch’s CEO, Hans Peter Külb
on the reverse side, so users don't have to worry about wear. Resilient polyester or polycarbonate film is used as the base material for front membranes. Customers can also choose from a variety of surface structures: glossy, matt or textured. Combinations are also possible, say matt membrane and gloss buttons.
Refinements such as electrical shielding, interchangeable
lettering and illumination styles are possible. Everything behind the membrane can be left to the supplier
who should advise on basic technologies (polyester dome, snap disk, etc) and take responsibility for the inner workings of the switching mechanism.
Incidentally, if the keystroke is extremely small, the effect can
be similar to sensor keys or touch panels. However, contacts remain electromechanical, there is no need for power assistance or controllers.
The front membrane and inner workings are sealed by a self-
adhesive layer. Thus, assembly is straightforward: remove the protective paper, lay the cables in position and stick on the membrane.
Membranes do have one disadvantage: the third dimension. If
a keypad needs to be long, wide and ‘high’, this is not so easy using a membrane.
Rubber switch mats are much better for higher profiles,
offering heights of up to several centimetres above the keypad surface. This type of keypad is used for applications including remote controls.
As you would expect with rubber (silicone rubber to be
precise), larger strokes and characteristic tactile response are achievable up to 4mm.
To ensure the assembly functions mechanically and 10 | May/June 2011 p12
www.electronics-sourcing.eu
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