HMI systems are utilized in ever expanding applications from power plant controls to the touchscreen of a cell phone. Typically these devices will have two primary components to function.
The first component is some form of input. The operator need a way to input instructions to the device and this is done through switches, touch screens, toggles, keypads and more.
The second important factor to a successful HMI system is output.
The machine has to inform the human that the commands were received and then information is displayed or a function is performed. Output could even be as simple as a status light blinking to indicate that it received commands.
Ergonomics and psychology have big influences on the HMI system industry as one of the main goals is to provide an easy, efficient and user friendly design for operating a machine.