The new Square Reader is 45 percent thinner than the previous version--a slimming that took careful consideration of the device's components. Photo: Josh Valcarcel/WIRED The effort was led by Square's VP of Hardware, Jesse Dorogusker, formerly the head of accessories at Apple. Photo: Josh Valcarcel/WIRED The old Square Reader (left) vs. the new Square Reader. Photo: Josh Valcarcel/WIRED The brains of the operation is a new custom chip. Here it is compared to the Reader itself. It's tiny. Photo: Josh Valcarcel/WIRED Square also developed a new custom read head--the piece that swipes data from the card itself. The two rectangles here draw from two different data bands hidden in the card's magnetic stripe. Photo: Josh Valcarcel/WIRED A close look at the flexible circuit board. Photo: Josh Valcarcel/WIRED The new Reader has a tapered lip on both sides, making it easier for customers to situate their card. Photo: Josh Valcarcel/WIRED The guts sitting in the plastic enclosure. Photo: Josh Valcarcel/WIRED The new chip allowed for a low power operation. It let Square ditch the coin cell battery of the previous version and draw all power from the smartphone via the audio jack. Photo: Josh Valcarcel/WIRED

When we talk about the design of a piece of hardware, we usually default to observations about its outward appearance–its form, its color, the materials it's made of. Often, though, that's only half the equation. For a product like the new Square Reader–a sleek update to the familiar credit card-swiping dongle that's nearly twice as thin as its predecessor–most of the design work is out of sight. It exists in the meticulous selection and arrangement of the components inside–the delicate stacking of circuitry and silicon that make our gadgets go. In this unseen world, every millimeter shaved is a victory. And in terms of getting tiny things even tinier, the new Square Reader makes for an excellent case study.

Jesse Dorogusker is used to working tiny. Before becoming Square's VP of Hardware, he spent eight years leading the accessories division at Apple, heading the development of the works-both-ways Lightning connector. With the new Reader, he had the chance to take a crack at a flagship product. Sitting in a booth in Square's immaculate new offices, huddled over a piece of paper with a dozen half-assembled Readers taped to it like bugs pinned to a science museum display, he detailed the challenge for WIRED.

What it Takes to Get a Perfect Swipe

The Square Reader has one job: swiping credit cards. Any new version of the device, then, had to improve on that single, simple function. We might take a card swipe for granted, but getting every detail right takes extreme care. You have to make the swipe feel satisfying; you have to make it ready accurately enough that it works the first, every time. Those two factors help convey something in the moment about Square itself: That the company is trust worthy, rock solid, and easy.

Some of that does involve the face Reader presents to the world. The new version is thinner than its predecessor, but it has a slightly larger footprint, giving customers and shop owners a slightly longer track for running cards. Both sides of the new device have tapered edges that make it easy to slot a card in, from either direction. (The former just had the open lip on one side.)

Improving that main swiping functionality also meant ditching many of the stock components the company had relied on for their previous card readers and building their own. One of the most important was an all-new read head, the piece that actually pulls the data off your credit card's magnetic stripe. In the old Reader, Square used a standard read head, more or less the same one that's been in every credit card reader and tape deck since 1985. Those worked well enough, but they were far from optimal. First, they weren't doing all they could to ensure successful swipes. The magnetic stripe on your credit card stores data in two separate bands. The old Reader grabbed from just one. With their new custom read head, Square can grab both, which makes every swipe more accurate, and more likely to work on one try.

>The team was able to fine-tune the friction customers feel.

The redesign also gave Dorogusker and company a chance to tweak the feel of the swipe itself, which is a crucial detail that makes the product itself feel trustworthy despite its tininess. By tweaking the design of the spring to which the magnetic read head was attached, the team was able to fine-tune the friction customers feel when swiping their card. At one point in development, they found that the level of contact they needed to successfully transfer data from a card resulted in a swipe that felt too loose. And when the swipe felt too loose, it felt like it wasn't working, and would thus require another swipe. So they increased the friction above what was actually needed–an adjustment that was overkill from a technical point of view but resulted in a swipe that felt perfect to the hand.

Developing custom components gave Square's hardware team a chance to rethink how the device was assembled, too. The company designed its magnetic read head so that it could be soldered to the circuit board in an oven, instead of by hand, allowing for far greater precision in its placement and a more streamlined manufacturing process. By reducing the tedious process of soldering to a more predictable one of oven-baking, the connections become more uniform, and thus more reliable. The whole device is less likely to loose some tiny connection that eventually makes the product wonky. The custom build also helped with size; off-the-shelf read heads are five millimeters plus; Square's own is just two-and-a-half.

How a Custom Chip Creates a Cascade of Consequences

The even greater undertaking with the new Reader, however, was the development of a custom chip, built from the ground up. "It's not typical for a startup to do that," Dorogusker says. "It's a little bit of upfront cost to build this from scratch." But the benefits were huge. After all, this tiny fleck is the brains of the operation. And by building their own chip, Square was able to improve several aspects of the product–its performance, its size, and its overall reliability–in one stroke.

On one level, developing a custom chip gave Square total control over the processes at the heart of the product: Decoding the magnetic signal from the credit card, encoding the electrical signal being sent to the smartphone, and all the encryption that happens in between. "We take all of that very seriously," Dorogusker says. "We know exactly what we need. Off the shelf solutions could do what we wanted but had a bunch of extra."

In terms of the design of the internals, though, the chip offered another fantastic advantage: an opportunity to ditch the Reader's battery. The old version relied on a coin cell, which added around two millimeters to the overall thickness of the device. With their own chip, though, Square was able to be much more efficient in their use of power, to the point that they could draw all they needed from the smartphone via the audio jack. As a result, the new Reader dropped the battery and two millimeters along with it. "For the nerds on the team, that is crazy awesome," Dorogusker says.

But ditching the battery meant more than saving space. It was also a huge step towards that simplicity Dorogusker set out to achieve from the start. "With a battery, you have to somehow connect the battery to your circuit board," he says. "You do that with two little wires. They have to be cut to length, stripped on both ends, tinned on both ends and hand soldered to the battery and then to the board. It's a huge amount of labor."

It's also the first thing that failed in Square's existing Readers—something the company gleaned from the broken units customers sent in to the office. A shop owner would drop the Reader enough times and eventually the wires would come loose. By eliminating the battery Square was able to eliminate the wires, too, ultimately making for a more robust product.

>A smart approach to a single component can yield all sorts of advantages.

It shows how a smart approach to a single component can yield all sorts of advantages. "It cascades through," Dorogusker says. "Designing our own electronics got us better performance, got rid of the battery and got rid of our biggest field issue all in one go."

Of course, building the new Square Reader involved tackling all those more outwardly visible design details. The device may be spartan in its aesthetic, but it isn't without its cosmetic improvements. It's 45% thinner than the old one, but, as mentioned earlier, its footprint is a bit wider. The card slot is more central to the device, instead of sitting just behind the front face, so that it's more intuitive to locate the slot without looking. The unit lost its bulky "shoulders," as Dorogusker puts it. And where the older Reader was quite obviously two pieces, a front and back, snapped together, the new one looks like one solid, unbroken piece of plastic. Only the closest inspection reveals the seam where the two pieces meet.

It's a small detail, but on such a simple device, shrinking that gap between the two parts of the enclosure has a significant effect. It makes the device seem more substantial, more considered, and generally higher quality. And yet, even after months of toiling on custom components to make the new Reader the most elegant credit card processing device in existence, Dorogusker still sees the product through the eyes of a Cupertino-bred perfectionist. He holds the new Reader between his fingers, pausing for a moment while he considers his creation. "I'd love to get rid of that seam."