Electronic Design

Know Your Options Before Choosing A Touchscreen

Though increasingly widespread and user-friendly, touchscreen technology is still very much a specialty and therefore outsourced by equipment manufacturers. But outsourcing any electronic subassembly can be a slippery slope for OEMs, since the end product ultimately will have their brand name on it.

Global manufacturers in the automotive, aircraft, and other major industries are experiencing quality issues that will testify to that. Meanwhile, OEMs developing new and innovative applications for touchscreen interfaces, whether handheld devices or elaborate systems, would do well to resolve some important issues before committing to a touchscreen design and supplier.

Partnering with your supplier Touch-based systems can get very complex and confusing. Naturally, vendors might specialize in a certain touchscreen technology or market segment to make them more competitive. But that also limits their flexibility, so they might not be the best supplier for other applications. Additionally, engineers should consider the volumes that the supplier normally produces. Some companies are geared to make large runs of a certain type of design, while others aren’t.

Choosing the right technology Different digital and analog touchscreen technologies will work in most applications. Analog resistive touch has achieved the greatest market acceptance and penetration. Yet this technology can present certain problems, such as drift (deviation) under certain conditions, whereas digital touchscreens do not exhibit any drift.

Designing for the environment Touchscreens are useful in most environments. But extreme temperatures, humidity, a corrosive atmosphere, electromagnetic interference, and even sound can affect them. And we’ve all experienced situations where touchscreens are hard to read due to lighting. That can be quite a handicap, and it results from not using the optimum materials, coatings, or filters. Some of these factors also may require the display to contain a combination of touchscreen technologies, such as membrane switches, analog keypads, LCDs, and LCD modules.

The pitfalls of drift One of the more serious pitfalls of touchscreen technology, drift, occurs when the touchscreen falls out of calibration so the touch point doesn’t correspond with the touch of the finger or stylus. This deviation most often occurs with analog electronic touchscreens that are exposed to extreme temperatures.

The standard acceptable linear deviation is 1.5%. That may be easy enough to achieve when a touchscreen is manufactured. But if it falls to 4% out of calibration, touch response could go off the map, and the consequences would be disastrous.

Drift often occurs because of conditions outside of the OEM’s control when the equipment is in the field for a while. It can occur because of the materials the touchscreen manufacturer has used or because of rough treatment by users.

There are other preventive design methods as well. When deemed appropriate, the manufacturer will use glass as one layer with an ITO deposit on glass, which is generally a harder, more durable surface than the ITO on more flexible, sputter-coated polyester.

Touchscreen sensitivity is another concern. The challenge can be, for example, to produce a touchscreen with the same pressure sensitivity required to actuate buttons that are also located on the controller. This can be a challenge, requiring touchscreen manufacturers to deliver a precise and highly customized finished product.

Manny Cardinale is the president of CAM Graphics Company Inc. He can be reached at [email protected].

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