So in the late '70s, Gates says, reed switches began to give way to keys that relied on a magnetic principle called the Hall Effect. These keyboards, made by Micro Switch and others, didn't use physical contact points to complete a keystroke -- instead they used magnetism, which can be less precise (and thus less liable to error) and doesn't require as many moving parts.
KeyTronic shows off the layers of its capacitive keyboards from the late '80s and early '90s. Credit: © KeyTronicEMS.
Click to view larger image.Meanwhile, Key Tronic, keen to get away from reed switches, developed the capacitive switch, which worked by putting a little bit of aluminum under the key top. When the key was depressed, that foil changed the capacitance of the circuit board underneath and a microprocessor registered a keystroke. This idea was soon improved upon with membrane keyboards, which simplified the capacitance mechanisms under the key and brought down production costs.
Trimming hardware, cutting costs
Though the materials sound cheap, keyboards were expensive in the early '80s. The typical keyboards Key Tronic and Micro Switch sold to computer makers ran about $100, as opposed to three or four bucks for the typical OEM keyboard today. To cut costs in a fiercely competitive market, keyboard manufacturers began to look for ways to cut hardware from the key while ensuring that the key tops, key weights, balance, foundation and "distance to travel" -- the space it takes to register a keystroke -- were familiar to users' fingers.
This required evaluating the hardware that makes the key move up and down. The "snap point" is one of the most important concepts that govern a keystroke, according to Aaron Stewart, a Lenovo senior design engineer reportedly nicknamed "Mr. Keyboard." This is the point where the key pops, your brain registers you've typed a letter and you pull back your finger. Think back to the first time you typed on a touch screen -- remember the shock of not having the snap point?
Additionally, keyboard makers have to consider the "break force" of the key, which has to provide enough resistance to allow your fingers to rest on the key top without inadvertently depressing it, but also needs to be weak enough to let you type without feeling like you're punching through a membrane with each keystroke.
Patented in 1978, the buckling spring key mechanism drove IBM's popular PC keyboards for years. Credit: Amir Yalon, CC by 2.0.
Click to view larger image.In 1978, IBM received a patent for a "buckling spring" key mechanism that mimicked the feel of the old Selectrics. The mechanism worked with a small spring attached to non-parallel surfaces under the keycap.
The spring coiled normally when depressed but "buckled" to the side at the snap point due to the non-parallel surfaces of attachment -- and created the familiar click-clack sound of IBM's popular Model M keyboard and other old keyboards. The buckled portion of the spring activated the circuit, which generated the keystroke.
In a rubber-dome keyboard (shown upside down), the key caps push down on the domes, which collapse, closing circuits and recording keystrokes, and then snap back. Credit: Aaron Siirila, CC by SA 2.5.
Click to view larger image.But cost cutting gave way to newer ways of suspending the key by IBM and other manufacturers. Rubber domes, which work with the same snapping principle as a toilet plunger, and scissor switches, which also have a rubber dome but use a scissoring mechanism attached to the key top to push down the dome, came to prominence in the late '80s and early '90s.
Part of the goal of the new designs was to reduce the distance of travel. Comfort and speed when typing depend on the distance of travel for the key on each stroke. Shaving off precious fractions of millimeters improved the typing experience for many users.
The scissoring mechanism used in scissor-switch keyboards shortens the distance a key must travel to record a stroke.
Credit: © Greg Raburn. Click to view larger image."Compared to historical examples, today's desktops and notebooks have roughly 40% less [distance to travel]," Lenovo's Hill points out. Typing on rubber-dome and scissor-switch keyboards is usually quieter as well.
These designs were also cheaper to produce, pushing keyboards to commodity status, according to Gates, and these two types of springs still underpin most of the computer keyboards on the market. Today the low-profile scissor-switch keys are typically found in notebooks and thin keyboards, including the chiclet-style keyboards on Apple's laptops. The taller rubber-dome keys are typically found in standard desktop keyboards and use an interlocking "chimney" structure in place of a scissors to stabilize the key travel.
As with any bygone technology, though, there are still enthusiasts who swear by the old IBM buckling springs. Indeed, keyboards with mechanical switches have undergone something of a renaissance in recent years as users pine for their crisp tactile feedback.