Yesterday's post was about trying to bring an Acer SW5-012 back to life, which was fortunately as easy as reseating a ribbon cable. One of the reasons I was so eager to crack that thing open was my fascination with its hinge attachment mechanism. This was one of the "convertible" machines launched in the Windows 8 era and evolution of the category continued to this day with computers like the Microsoft Surface Book.

The hinge attachment/release mechanism for the Surface Book featured precisely machined components and electronics to control a wire of memory alloy. This Acer is a much cheaper machine so its nifty connector must also be simpler. Before I pried it open, I mentally tried to figure out how I would design such a mechanism.

At the time I thought the battery was flat, so I excluded any electronics in the design. It had to work without power, which made me think about magnets. A few small magnets to detect when the base is close to the screen, and pull against some spring-loaded arms to hold the thing together. When I pull on the screen, the force overcomes the springs to releases the arms.

Once I popped off the back cover of the computer, I could check my design against the answer and... well, I got the magnets part right even though it was based on a false premise (the battery was not flat like I thought.) And all the spring-loaded arms and clips and levers? Unnecessary complexity. I knew it had to be simpler than the Surface Book mechanism, but it was far simpler than what I imagined.

The actual mechanism consisted of magnets and... that's it. Just some very cleverly placed magnets. When the screen is installed on the base, the magnets attract like we expect them to do, holding things together.

Acer Hinge Engaged

So what happens when we lift the screen away from the base? What's causing that mechanical "click" sound?

When the base is lifted, the magnets in the screen is pulled away from the magnets in the base. Lacking the strong attraction, the magnets in the screen searched for the next best thing and finds a few metal plates slightly recessed into the cavity. The "click" is the magnet moving from the no-longer-there base magnet to the metal plate. When the magnets are attached to this inner metal plate, they are a few millimeters away from the edge of the unit but that's far enough to keep it from picking up errant metal bits (paperclips, staples, etc.) while it is in tablet mode.

Acer Hinge Released

When the screen is reinstalled on the base, the screen magnet leave the metal plate in favor of the magnet in the base, making another "click".

The Acer manual called it the "Acer Smart Hinge" and I agree it's very smart - on the part of the people who designed it. Its simplicity lends to lower manufacturing cost and also to its reliability - no springs to break, no latch to wear out.

I am impressed.