Design Guidelines for Control Feel and Feedback
4/8/2010
The following factors contribute to the control feel and feedback.
Tactility
All buttons and controls should return a crisp tactile response. This is an essential part of device and interaction feedback. It is especially important for users who choose to turn off device–generated sounds for button pushes. Dome–type switches typically used in navigation keys (d–pads), keypads and keyboards tend to have a large quality variations; hardware designers and engineers should take appropriate steps to control for production variation and quality to ensure button tactility is acceptable.
Reasonable Effort or Force–to–Fire (FTF)
Ensure that switches on hardware require reasonable effort. Too little effort, or force–to–fire (FTF) can result in inadvertent actuations and poor tactility. Too much effort can result in too much muscle strain for easy operation and possible repetitive stress injuries (RSI) for the user. Though the normal range of FTF varies widely by user preference and design implementation, a rough guideline for consumer market devices is that FTF should be between 100 and 300 grams (0.1–0.3 N) for d–pad, 12–key keypad and QWERTY keyboards. This is a wide range, and optimal FTF will vary by application, user group, individual user and device purpose. OEM usability testing is highly encouraged. For instance, vertical–market devices will likely require different considerations than consumer market devices.
UI Transitions and Latency
Interface transitions that occur due to direct user input, for example, pushing the volume buttons or the action button of the d–pad, should not be slower than is deemed acceptable as established by usability studies. High latency leads to measurable decreases in user satisfaction with their device. Users will often compare a high–latency device with previous devices they have owned, or other devices in the market, and will associate this with poor performance.