A touchscreen is a touchscreen, right? Hardly!  As MOTO pointed out in our recent Do-It-Yourself Touchscreen Analysis post, “All touchscreens are not created equal.”

With our simple test technique — which basically consists of using a basic drawing application and a finger to slowly trace straight lines on the screen of each device — it’s easy to see the difference in touchscreen resolution from one phone to the next.  Results with straight lines indicate a high degree of sensor accuracy; less-precise sensors show the lines with wavy patterns, stair-steps, or both.

After we published our first comparison of four touchscreen smartphones, a few critics found fault with our DIY testing technique. Many of of these comments centered around the idea that our human-finger methodology is prone to inconsistency, due to variables in finger pressure, line-straightness, or tracing speed.

Human Error?

Our response to these arguments is pretty simple: These are all fair points. Nevertheless, we’re confident that such inconsistencies do not distort the basic results of our touchscreen shootout. In other words, the inconsistencies are real, but they don’t make much difference.

Nevertheless, to satisfy the critics, we decided to give them exactly what they asked for: We wrote a script for MOTO’s laboratory robot and then re-ran the comparison to see how the touchscreens stack up when the lines are drawn by our robot’s slow and precise “finger.” (See the robot in action, in video below.)

Add Some New Contenders

Before running the robot test, we also decided to satisfy the many requests we received to add the Palm Pre and the Blackberry Storm 2 to the mix. How did the new phones perform? The Blackberry and the Palm touchscreens both performed fairly well. The iPhone still retains its crown as King of the smartphone touchscreens, with the Nexus One in a distant second. Take a look:

Understanding the Results

Touchscreen performance variation occurs because there is no out-of-the-box solution for manufacturers that hope to install multi-touch screens in consumer electronic devices.

To get it right, gadget-makers have to assemble a variety of critical elements — screen hardware, software algorithms, sensor tuning, and user-interface design, to name but a few — and then refine each component of the stack to deliver the best touchscreen experience possible. It’s a complex and laborious process that requires extremely close collaboration between multidisciplinary teams, as well as a high-level vision for a quality end-user experience.

Indeed, from a consumer perspective, what matters most isn’t the performance of the touchscreen itself, but how well a touchscreen performs in combination with its operating system and user-interface to deliver an experience that is satisfying overall.

Still, it’s useful to look at touchscreen performance in isolation, because it is a central ingredient in the mix and a good indicator of how satisfying a touchscreen experience is likely to be.

Watch the video for the full story.  (Mobile viewers click here.)

Does the Drawing App Make a Difference?

Some readers who saw our last DIY Touchscreen Analysis post wondered what drawing applications we used, and if the drawing application could influence the results by either compensating for or distortng hardware performance.

Developers who create drawing apps sometimes add smoothing algorithms to make the input look more natural.  However, the artifacts of these algorithms are fairly easy to identify with casual exploration.  We chose drawing applications which we found not to do minimal (if any) smoothing of the input data.

In any case, smoothing is most effective only if you are moving quickly – with the snail-like pace of the test robot, you can see that the data, as captured, appears immediately on the screen and never changes to a “smoothed” version.

Of course you don’t have to take our word for it – try it yourself!  Here are the apps we used:

• Blackberry Storm: Canvas
• iPhone: SimpleDraw
• Droid Eris, Droid: DrawNoteK
• Palm Pre: Super Paint
• Google Nexus One: SimplyDraw

Human v. Robot

Finally, as predicted, the lineup below shows how our simple finger-test correlates quite closely with the more formal results when we got when we used our ultra-precise, ultra-consistent robot in MOTO’s laboratories:

Indeed, notice that by and large, the results look even worse in the robot tests.  That’s because the robot drew lines at only a quarter-inch per second — much more slowly than our ” DIY test.

And as we we’ve explained previously, low speed is crucial to testing the true performance of the screen, because tracing high speeds skips over the many data points captured at slow speed, causing lines to look straighter than they actually are. Because the robotic finger is somewhat less compliant than a human finger, it is a little harder to detect. This confuses poor screens even more than when humans attempt the test.

A Prediction

In the long run, however, we don’t expect this high degree of touchscreen variation between handset manufacturers to continue in such dramatic form.

Right now, capacitive touchscreens are a relatively new feature to appear in consumer electronics products. And as we’ve pointed out several times before, creating a seamless touchscreen experience is hard work that requires a high level of commitment to technology integration and interdisciplinary teamwork. Over time more brand-name manufacturers will acquire the expertise required to deliver excellent touchscreen products.

We know for a fact that the solutions in these phones (other than the iPhone) are all last-generation silicon and touch panel components – the other touch screen makers are hard at work perfecting their new solutions, and they may just leapfrog Apple in some areas when they arrive on the market over the next year.

Just consider the “door slam test” that’s often used to evaluate the build-quality of automobiles. Like touchscreen devices, cars are complex machines that require a high level of system integration. A decade ago, the difference in quality between established manufacturers like BMW or Mercedes and a relative newcomer like Hyundai was dramatic. A door-slam on the former felt solid and precise; the latter felt loose and tinny. Yet today Hyundai has closed the gap, and many of the company’s cars pass the door-slam test in world-class style.

In other words, practice can help make perfect. It’ll be interesting to re-run our touchscreen test a year or two from now to see how the playing field starts to even-up.

The success of the iPhone has triggered the adoption of touchscreen systems in a wide range of mobile devices, and a bevy of new gadgets equipped with capacitive sensing technology have now hit the market.  MOTO has years of experience developing products that use capacitive touch, and we’ve had the opportunity to test many of the latest devices. Our conclusion: All touchscreens are not created equal.

It takes finesse to create a touchscreen system that’s pleasant to use, because touchscreens require seamless integration between hardware components, software algorithms, and user-interface design. If a manufacturer cuts corners or flubs any of the critical elements, the user’s experience with a touchscreen product is likely to suffer.

Simple and True

Although we usually use sophisticated tools to test touch screen accuracy, MOTO has also developed a simple technique anyone can use to evaluate the resolution and accuracy of a touchscreen device. All you need is a basic drawing program (download one if necessary), a steady hand, and a few straight lines drawn very slowly on the screen.

This video shows what happened when we recently took several touchscreen systems out for a test drive:

The Virtue of Slow

Why do you need to draw slowly?  On a good touchscreen, users can draw clean straight lines, even while going very slowly, so the graphics that appear on screen accurately represent what was physically drawn.

On inferior touchscreens, it’s basically impossible to draw straight lines. Instead, the lines look jagged or zig-zag, no matter how slowly you go, because the sensor size is too big, the touch-sampling rate is too low, and/or the algorithms that convert gestures into images are too non-linear to faithfully represent user inputs.

Pressure Matters

Also, even on a single device, the amount of pressure and the part of the finger you use on the screen has an impact on how well it senses. A good touchscreen device will produce linear output regardless of whether you’re using the full pad of your finger, or just the dry corner of your cuticle.  When comparing devices, make sure to use even pressure across all of them.

If you want to show the most extreme case, draw very lightly with the corner of your finger. The artifacts will increase significantly, showing which device is really the best with a weak signal. This is important because quick keyboard use and light flicks on the screen really push the limits of the touch panel’s ability to sense.

Here you can see the results of our test:

Edge Performance

Take careful note of the performance at the edges of the screen. The performance at the edge is challenging to tune, and separate from the basic “waviness” test. The iPhone tracks all curve very strongly as you approach the edge of the screen, despite a straight finger trajectory. This is especially obvious at the bottom, where the iPhone has a sensitivity problem.

The Droid Eris [Nexus One] is actually the clear winner for edge performance — the signal tracks right off the edge of the screen very consistently.

[edit] As of time of first writing, we hadn’t tested the Nexus One.  It does slightly better than the Eris.  In fact, they both use the same touch controller IC.

A Quest for High Signal-to-Noise Ratio

To create a superior touchscreen experience, it’s essential to develop a touchscreen sensor that has the highest possible signal-to-noise ratio, or SNR. When a manufacturer gets it right, the device tracks touch inputs almost as if they were connected to physical objects in the real world. Get it wrong and consumers end up with inferior touchscreen systems that are inaccurate, insensitive, and absolutely infuriating to use for typing.

Key drivers of SNR include:

• Conductive sensor material
• Substrate material
• Substrate thickness
• Distance from display (the biggest noise source)
• Sensing waveform
• Sensor pattern
• Sensor pitch
• Analog sensing circuitry
• Sample rate

Touchscreens are a catalyst for innovation and a powerful way for device manufacturers to differentiate their products in an intensely competitive marketplace. But as our demonstration shows, there’s a right way and a wrong way to deploy the technology. MOTO has worked with capacitive touch interfaces for more than 15 years, and here are some essential dos and don’ts for anyone entering the field:

• Don’t skimp on materials. With touchscreen hardware, manufacturers get what they pay for — and consumers will notice the difference.
• Allow ample time to develop your algorithms. Don’t treat touchscreen algorithms as an element of component sourcing; for best results, create a distinct touch development track under your own roof to make sure your products are both responsive and accurate.
• Closely integrate touchscreen hardware, software, and user interaction development, and do so as early as possible in the product development process. Never treat them as separate tasks.