Displays
Displays are one of the primary ways an embedded device communicates with its user. The display technologies commonly used with ESP32 boards fall into three main families: LCD, OLED, and e-paper. Their pixels are integrated into a continuous panel. LCD includes the reflective RLCD variant, while OLED includes passive-matrix OLED (PMOLED) and active-matrix OLED (AMOLED). LED matrices form a separate category because each pixel is an individually packaged LED. These technologies trade off color, power consumption, refresh rate, and readability, so the right choice depends on the application.
This page compares the main display types. The remaining pages explain how each technology works and how to drive it.
1. Display Types at a Glance
- LCD: Uses a backlight shining through a liquid-crystal layer. LCDs are a general-purpose, cost-effective choice for full-color user interfaces.
- RLCD: A reflective LCD that uses ambient light instead of a backlight. It offers very low power consumption and excellent sunlight readability, making it suitable for always-on, low-power devices.
- OLED: Uses self-emissive pixels and therefore requires no backlight. Small monochrome modules, such as common 0.96-inch displays, are usually passive-matrix OLEDs (PMOLEDs) suited to status information.
- AMOLED: Uses active-matrix OLED rather than PMOLED. AMOLED panels provide full color, high contrast, and high resolution and are commonly used in compact devices such as smartwatches.
- E-paper: Uses electrophoretic ink. A static image consumes no power to maintain and looks similar to printed paper, but updates are slow. E-paper is well suited to electronic shelf labels, calendars, and other infrequently updated displays.
- LED matrix: Arranges individually packaged LEDs in rows and columns, with one LED package per pixel. LED matrices are bright and can be tiled into large displays, but their coarse pixel pitch limits resolution. They are intended for signs and information displays viewed from a distance.
2. Technology Comparison
Use the following questions to identify the display types that fit the application, then compare their details in the table:
- Need a full-color GUI? → LCD or AMOLED. Text and icons only? → OLED, RLCD, or e-paper.
- Battery-powered with long runtime? → Choose e-paper when the image changes infrequently, or RLCD when it must remain visible and update in real time.
- Strong ambient light? → Prefer reflective displays such as RLCD or e-paper. Need a large, bright display viewed from a distance? → LED matrix.
- Display quality is the priority? → AMOLED provides the highest contrast and color performance, generally at the highest cost.
“Sunlight readability” describes how easily a display can be read under strong ambient light. It does not mean the display is designed for prolonged exposure to direct sunlight.
Long-term exposure can cause overheating, UV degradation, adhesive aging, polarizer damage, uneven output, and reduced contrast. Even reflective technologies such as RLCD and e-paper require a module or enclosure rated for the application's temperature range, moisture exposure, and UV conditions.
| Display type | Operating principle | Color | Power consumption | Refresh rate | Sunlight readability | Typical applications |
|---|---|---|---|---|---|---|
| LCD | Backlight filtered by liquid crystals | Full color | Medium; mainly the backlight | Fast | Fair | General-purpose GUIs, instrument panels |
| RLCD | Liquid crystals reflecting ambient light | Monochrome / limited color | Very low | Fast | Excellent | Always-on watches, outdoor devices |
| OLED | Self-emissive organic pixels | Usually monochrome / two-color | Low; black pixels consume no power | Fast | Fair | Status displays, compact instruments |
| AMOLED | Active-matrix self-emissive pixels | Full color, high contrast | Low to medium | Fast | Good | Smartwatches, high-end interactive devices |
| E-paper | Electrophoretic ink | Black and white / three-color / full color | None while holding a static image | Slow; typically seconds | Excellent | Electronic shelf labels, calendars, readers |
| LED matrix | Self-emissive LED packages | Full color / monochrome | High; requires a high-current supply | Fast | Excellent at high brightness | Signs, information boards, scoreboards |
3. Pages in This Guide
Interfaces, touch input, and GUI software are largely independent of the underlying panel technology. This guide includes:
- Display Fundamentals and Interfaces: Pixels, color depth, framebuffers, and the differences among SPI, QSPI, I80, RGB, and MIPI-DSI interfaces.
- LCD
- RLCD
- OLED
- AMOLED
- E-paper
- LED Matrix
- Touch Input: Resistive and capacitive touch, common touch controllers, coordinate reading, and rotation mapping.
- GUI Frameworks: Choosing among LVGL (Light and Versatile Graphics Library), u8g2, and other graphics libraries.