A human machine interface (HMI) is an interface which permits interaction between a human being and a machine. Human machine interfaces vary widely, from control panels for nuclear power plants to the screen and input buttons on a cell phone. Designing such interfaces is a challenge, and requires a great deal of work to make the interface functional, accessible, pleasant to use, and logical. Some engineers specialize in developing human machine interfaces and changing the ways in which people interact with machines and systems.
Two components are needed in a human machine interface. The first is an input. A human user needs some way to tell the machine what to do, to make requests of the machine, or to adjust the machine. Examples of input devices include keyboards, toggles, switches, touch screens, joysticks, and mice. All of these devices can be utilized to send commands to a system or even an interlinked set of systems.
The interface also requires an output, which allows the machine to keep the human user updated on the progress of commands, or to execute commands in physical space. On a computer, for example, users have a screen which can display information. A robot, on the other hand, may move in response to commands and store data on a hard drive so that people can see how the robot responds, learns, and navigates the world. Outputs can also include things as simple as status lights which alert people when toggles or switches have been activated.
The technology behind the human machine interface is constantly improving. Researchers have developed interfaces which can be controlled with the mind, for example, seeing applications for this technology among stroke patients and other people with severely restricted modes of communication. Likewise, outputs have become much more sophisticated over time.
As many people have noted, a poorly designed human machine interface can be extremely frustrating. On one end of the scale, the interface may be buggy or nonfunctional, causing difficulty because it does not work as intended. On the other end of the scale, the interface works, but it is designed in such a way that it is confusing and challenging to operate because it is not intuitive for users. The art of designing intuitive interfaces requires a deep understanding of how humans interact with their environment and an awareness of the psychology of designing interfaces in a way which will be accessible to a broad spectrum of humans. What works for an engineer in a human machine interface, for example, might not be as easy for a member of the general public.