R – Things to consider when writing for touch screen


I'm starting a new project which involves developing an interface for a machine that measures wedge and roundness of lenses and stores the information in a database and reports on it. There's a decent chance we're going to be putting a touch screen on this machine so that it doesn't need to have a mouse or keyboard…

I don't have any experience developing for full size touch screens, so I'm looking for advice/tips/info from you guys…

I can imagine you want to make the elements a little larger than normal… space buttons out a bit more…. things like that… anyone have anything else to add?

Best Solution

A few things to consider:

  • You need to account for parallax error when touching controls. Basically, the user may touch the screen above or below your actual control and therefore miss the control. This is a combination of the size of the control (eg you can have the active area larger than visual control to allow the user to miss and still activate the control), the viewing angle of the user (which you may or may not be able to predict/control) and the type of touch screen you're using. If you know where the user will be placed relative to the screen when using it, you can usually accommodate this with appropriate calibration.

  • Depending on the type of touch screen, you may need to ensure that your users aren't wearing gloves or using an implement other than their fingers (eg the end of a pen) to touch the screen. Some screens (eg those depending on conductance) don't respond well to anything other than flesh and blood.

  • Avoid using double clicks because it can be very hard for users to reliably double click a control. This can be partly mitigated if you've got experienced/trained users working in a fairly controlled environment where they're used to the screens.

  • Linked to the above, if you are using double clicks, you may find the double click activated when the user only wants to single click. This is because it's very easy for the user's finger to bounce slightly on touching the screen and, depending on how sensitive the double click settings are, trigger a double rather than a single click. For this and the previous reason, we always disable double clicks and only use single clicks (or similar single activation controls).

  • However big you think you need to make the controls to allow for touch activation, they almost certainly need to be bigger still. Make sure you test the interface with real users in the real deployment environment (or as close to it as you can get). For example, we deployed some screens with nice big buttons you couldn't miss only to find that the control room was unheated and that the users were wearing thick gloves in the middle of winter, making their fingers way bigger than we had allowed for.

  • Don't put any controls near the edges of the screen - it's very hard to get your finger into the edges (particularly if the screen has a deep bezel) and a slight calibration problem can easily shift the control too close to the edge to use. Standard menus and scroll bars are a good example of controls that can be very tricky to use on a touch screen and you should either avoid them (which is preferable - they're not good for touch screens) or replicate them with jumbo equivalents.

  • Remember that the user's hand will be over the screen, obscuring some of the screen and controls (typically those below where the user is touching, but it depends on the position of the user relative to the screen). Don't put instructions or indicators where the user's hand or arm will obscure them when trying to use the control they relate to (eg typically put them above rather than below the control).

  • Depending on the environment, make sure your touch screen is suitably proofed against dust, damp, grease etc and make sure it's easy to clean without damaging it. You wouldn't believe the slime that can quickly accumulate on a touch screen in an industrial or public setting.

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