Display Systems Overview

Introduction

The Human-Machine Interface (HMI) serves as the bridge between a robot and its operator. A well-designed HMI intuitively communicates robot status, receives operator commands, and enhances the user experience. Robot HMI encompasses three major feedback channels: visual, auditory, and haptic.

HMI Architecture

graph TD
    subgraph Output Channels [Feedback Channels - Robot to Human]
        V[Visual Feedback] --> D[Display<br/>OLED/LCD/Touchscreen]
        V --> L[LED Indicators<br/>Status/RGB Strips]
        A[Auditory Feedback] --> B[Buzzer]
        A --> S[Speaker<br/>Voice/Sound Effects]
        H[Haptic Feedback] --> VIB[Vibration Motor]
    end

    subgraph Input Channels [Control Channels - Human to Robot]
        BTN[Physical Buttons/Knobs]
        TS[Touchscreen]
        RC[Remote Controller/Gamepad]
        WEB[Web Interface]
        VOICE[Voice Commands]
    end

    subgraph Processing [HMI Controller]
        MCU_HMI[MCU/SBC]
    end

    D --> MCU_HMI
    L --> MCU_HMI
    B --> MCU_HMI
    S --> MCU_HMI
    BTN --> MCU_HMI
    TS --> MCU_HMI
    RC --> MCU_HMI
    WEB --> MCU_HMI
    VOICE --> MCU_HMI

    MCU_HMI --> |ROS2/Serial| ROBOT[Robot Main Controller]

HMI Requirements for Different Robots

Robot Type	Display Needs	Control Method	Feedback Focus
Educational/Entry-level	LED + Small OLED	Buttons/Remote	Simple status indication
Service Robot	Touchscreen + LED	Touchscreen/Voice	Rich UI/Voice interaction
Industrial AGV	Status lights + Small screen	Web interface	Warning/Error status
Quadruped/Humanoid	LED strip + Web	Gamepad/Web/APP	Motion status/Camera feed
UAV	Ground station	RC controller	Flight data/Real-time video
Competition Robot	Minimal	RC/Autonomous	Key parameters

Display Technology Overview

Technology	Resolution	Color	Power	Visibility	Cost	Application
Single LED	—	Mono/RGB	Very low	Long range	$0.1	Status indication
LED Strip	—	RGB full color	Low-Med	Medium range	$3-10	Ambiance/Status
OLED 0.96"	128×64	Mono/Dual color	Very low	Close range	$3-5	Parameter display
TFT LCD 2.8"	320×240	Full color	Medium	Medium range	$8-15	Graphical interface
e-Paper	Various	B&W/Tricolor	Very low (refresh)	Excellent in sunlight	$10-30	Static information
7" LCD	800×480+	Full color	Med-High	—	$30-60	Full GUI
7" Touchscreen	800×480+	Full color+Touch	Med-High	—	$50-80	Interactive interface

Feedback Design Principles

Status Levels

Robot status should be displayed in levels so operators can quickly assess the situation:

Level	Color	Meaning	Display Method
Normal Operation	Green	All clear	Green solid/breathing
Attention	Yellow	Needs attention	Yellow blinking
Warning	Orange	Degraded performance	Orange fast blink+buzzer
Error	Red	Intervention required	Red fast blink+alarm
Emergency Stop	Red	Stopped	Red solid

Information Hierarchy

graph LR
    L1[Layer 1<br/>LED Color/Pattern] --> L2[Layer 2<br/>OLED Brief Info]
    L2 --> L3[Layer 3<br/>LCD/Touchscreen Details]
    L3 --> L4[Layer 4<br/>Web Interface Full Data]

    L1 -.-> |Long range| USER[Operator]
    L2 -.-> |Close range| USER
    L3 -.-> |Interaction range| USER
    L4 -.-> |Remote| USER

• Layer 1 (LED): Long-range quick assessment -- normal/abnormal
• Layer 2 (OLED): Close-range viewing -- battery, IP address, key parameters
• Layer 3 (LCD/Touchscreen): Detailed operation -- menus, settings, debugging
• Layer 4 (Web Interface): Full control -- camera, map, logs

Interaction Design Principles

1. Simple and Intuitive: Key information at a glance, avoid information overload
2. Immediate Feedback: Provide visual/auditory confirmation immediately after operation
3. Error Tolerance: Confirmation steps for misoperations, emergency stop always accessible
4. Consistency: Maintain uniform colors, icons, and operational logic
5. Accessibility: Operators can see/reach critical controls in any posture
6. Graceful Degradation: LEDs still provide basic status when displays fail

Chapter Structure

This chapter covers the components of robot HMI in detail:

• OLED and LCD: Display selection and driving
• LED Indicators and Sound: Status lights and audio feedback
• Touchscreen and Web Interface: Graphical interaction
• Remote Control and Gamepad: Remote control solutions

References

• About Face: The Essentials of Interaction Design
• Material Design Guidelines (Google)
• LVGL Documentation: lvgl.io
• ROS2 Visualization Tools

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