HMI, MMI & Displays

The most important information in brief

– HMIs and MMIs are operator interfaces and display units between humans and machines.

They display information and allow input via keys, touch, or other controls.

- They support operation, diagnostics, status display, and process guidance.

What do HMI and MMI mean?

HMI stands for Human Machine Interface, and MMI stands for Man Machine Interface. Both terms describe the interface through which a person interacts with a machine, vehicle, device, or system. In many projects, the terms are used similarly. It refers not only to the visible display but to the entire operating and display concept.

Several components can belong to an HMI or MMI: a display, mechanical buttons, rotary encoders, touch surfaces, status LEDs, acoustic signals, housing parts, connectors, printed circuit boards, software modules, and communication interfaces. Depending on the application, the control panel is either directly integrated into a machine, designed as a separate control unit, or incorporated into a vehicle cockpit.

From a project perspective, work does not begin with selecting a display, but with clarifying the tasks of the operating device. It must be determined which information is to be displayed, which inputs should be possible, and which states the system must clearly report back. This includes start-up and operating states, error messages, warning notices, parameter inputs, menus, status indicators, and diagnostic information.

An HMI is always connected to an overall technical system. It receives data, displays it, and forwards user inputs. Interfaces must be defined for this. In machines, these can be connections to controllers, sensors, or actuators. In vehicles, control units, onboard networks, and bus systems are often added. The user interface is therefore not an isolated software topic, but a component of the system architecture.

PICKPLACE therefore considers HMI and MMI projects on multiple levels. The hardware must be suitable for the display, input method, and environmental conditions. The mechanical installation must take into account space, mounting, cable management, and operability. The software must map display content, inputs, state logic, and communication. Only through the interaction of these parts is an operating and display unit created that can be used in the intended system.

What does a machine or vehicle need a display for?

A display makes technical states visible. Machines, vehicles, and devices generate a lot of internal information that would otherwise only be recognizable via measuring devices, diagnostic interfaces, or control data. A display can show operating states, measured values, warnings, error codes, step sequences, operating instructions, or process data. This transforms internal system information into understandable feedback for operation, maintenance, or commissioning.

In a machine, a display can show, for example, whether a process has started, is paused, or has finished. It can display parameters, allow inputs, or make the current state of assemblies visible. In case of malfunctions, it can provide indications of which component is affected or which state should be checked first. This makes the display a tool for operation and diagnostics.

In a vehicle, a display often performs multiple tasks simultaneously. It can show system status, operating modes, warning messages, settings, or information from connected control units. Depending on the project context, the display is permanently integrated into a cockpit, an operating panel, or a separate housing. The connection to the vehicle communication must be designed accordingly so that the displayed information comes from the correct data sources and inputs are forwarded to the intended recipients.

A display is also needed when a technical system goes through different states that must be distinguishable by the user. These include start-ups, initialization, normal operation, fault status, service status, or shutdown. Without a clear display, it can remain unclear whether an input has been accepted, whether a process is still running, or whether there is an error. The HMI reduces this ambiguity by making system states visible and integrating inputs into a traceable process.

For the project design, the question of which display technology, size, resolution, and form factor is needed arises early on. This selection depends on what information is displayed, how frequently input is made, and under what conditions the system is operated. For purely status feedback, a simple display may suffice. If menus, diagnostic views, or graphical process representations are planned, different requirements are placed on the display, response behavior, and software structure.

In such projects, PICKPLACE also clarifies whether a touchscreen is sensible or if buttons, rotary encoders, or other controls are the better solution. Touch operation can consolidate many functions in one area, but it is not the right input method for every environment. Mechanical buttons can be useful when operation is to be performed without eye contact, with gloves, or under changing environmental conditions. The decision affects not only the operation but also the housing, electronics, software, and testability.

What makes a good user interface?

A good user interface clearly represents the system's actual processes. It doesn't just display data but organizes it in such a way that operators can recognize states, understand inputs, and react specifically to deviations. For this to happen, functions, displays, and input steps must be developed from the process itself.

The process begins with the question of which user groups will work with the HMI. An operator during normal operation needs different information than someone setting up, maintaining, or troubleshooting a machine. Therefore, an interface can include multiple levels: an operating view, adjustment pages, diagnostic views, or service functions. Not all information needs to be constantly visible. The crucial factor is that the required information is available in the appropriate place.

The operating logic must align with the technical states. For example, if a system only releases certain functions after successful initialization, this must be apparent on the interface. If an input is not possible, the reason should be derivable from the state. Error messages must be formulated and structured in a way that matches technical diagnostics. An error text without a connection to the actual state makes troubleshooting more difficult.

The display of status information also requires precise decisions. Colors, icons, text, and numerical values must be used consistently. If multiple operating states exist, their differentiation must be recognizable in the interface. When limit values, alarms, or warnings are displayed, it must be clarified which data source is definitive and how updates occur. In this process, the software architecture is directly linked to the user interface.

A user interface is also dependent on hardware. Display size, resolution, brightness, viewing angle, input elements, and mounting orientation influence how content can be designed. A layout that works on a large display can become unreadable on a small control panel. A touch surface requires different spacing and control sizes than a menu navigated by buttons. Therefore, design, hardware selection, and mechanical installation are considered together.

For PICKPLACE, developing a user interface also involves harmonizing display, input, and system communication. A button or a touch field not only triggers a graphical response but also, in many cases, sends a command to a controller or control unit. Conversely, the HMI must process feedback and update the displayed status. This requires signals, data points, telegrams, or interface descriptions.

Good user interfaces are not created with graphic design alone. They require a clear structure of functions, a clear assignment of states, and technical implementation that suits the hardware and system environment. Therefore, projects examine which information is to be permanently displayed, which menus are needed, which inputs need to be confirmed, and how error states are made visible.

Typical Techniques and Systems

• GUI Stack LVGL
• GUI Tool STM32CubeGFX
• GUI Framework Qt for MCUs
• Manufacturer Riverdi
• Manufacturer Waveshare

Our Services

PICKPLACE supports HMI, MMI, and display projects from technical clarification to the implementation of individual assemblies or software components. The scope of services depends on the project status: some tasks begin with a new control and display unit, others with the further development of an existing panel, or with the integration of a display into an existing system.

In hardware development, we work on the electronic foundation of the control unit. This includes selecting and integrating a display, arranging the operating elements, designing interfaces, and integrating the necessary electronics. If buttons, touch controls, rotary encoders, or status indicators are planned, these components are incorporated into the electrical and functional structure. It must be clarified which signals are processed internally and which data are transmitted to the higher-level system.

When designing the user interface, we support the structuring of views, menus, status indicators, and input steps. The focus is on clearly displaying technical states and aligning operation with actual processes. To achieve this, display content, operating paths, feedback, and error representations are defined. The design is coordinated with the available display area, input method, and technical data sources.

Mechanical integration is a separate part of the project. A display or control panel must be integrated into a housing, machine, vehicle, or existing assembly. Installation space, mounting, accessibility, cable routing, connector positions, and operating positions must be considered. PICKPLACE considers mechanical integration along with electronics and the operating concept so that the structural implementation does not conflict with operability or wiring.

In the area of software, we develop or extend functionalities required for display, input, and state processing. This includes graphical user interfaces, menu logic, display of measured values, processing of user inputs, feedback to the user interface, and mapping of operating or error states. Depending on the system, the software can run on a microcontroller, an embedded system, or an existing control platform.

Another focus is bus connectivity. HMI and MMI systems often need to exchange data with controllers, control units, or other electronic components. PICKPLACE supports connection to existing communication structures, the definition of required data points, and the implementation of interface logic. This determines which information is received, displayed, processed, or sent.

If an existing HMI is causing problems, work can begin with an analysis. This involves checking hardware, software, operating logic, and communication. Typical questions include: Are the correct data being displayed? Does the interface react appropriately to system statuses? Are inputs clearly assigned? Are there delays, unclear error messages, or discrepancies between the display and the actual status? Corrections, enhancements, or a redesign can be derived from the results.

PICKPLACE can handle HMI, MMI, and display topics as part of a larger development project or as a distinct work package. It is crucial that display, input, mechanics, electronics, software, and bus communication are specified together. This creates an operating and display unit that matches the system's technical functions and covers the intended tasks in operation, diagnostics, status display, and process control.