液晶ディスプレイ選びに悩む? 私たちのガイドでは SPI について説明します, I2c, RGB, LVDS, およびMIPIインターフェース, 解決, PPI, and more to help you select the perfect display for your embedded project.
導入
Selecting the right LCD display can be one of the most critical—and confusing—steps in an electronics project. Whether you’re building a smart home device, a portable gadget, or an industrial control panel, the display is your project’s face to the world.
With a maze of acronyms like SPI, RGB, LVDS, MIPI, and parameters like resolution and PPI, how do you make the right choice? This guide will demystify the process. We’ll break down the key factors, starting with the most fundamental: the インタフェース.
Part 1: The Digital Highway – Choosing the Right Display Interface
The interface is the communication channel between your microcontroller (MCU) or processor (MPU) and the display. It dictates the speed, complexity, and ultimately, the feasibility of your design.
あ. Low-Speed Interfaces: For Simple, Small Displays
1. spi (シリアルペリフェラルインターフェイス)
How it Works: A simple, synchronous serial protocol using a clock, data out, data in, and a chip select line.
Pros: Very few pins required, simple wiring, easy to code, universally supported by almost all MCUs.
Cons: Extremely limited bandwidth; the slowest option for graphical displays.
Ideal For: Small TFT displays (typically under 2 インチ) with low resolutions (例えば, 128×64, 240×240). Perfect for showing static text, simple icons, or slow animations in wearables and small instruments.
The Bottom Line: The king of simplicity and pin-efficiency for basic graphics.
2. I2c (Inter-Integrated Circuit)
How it Works: A two-wire serial protocol (SDA and SCL) that supports multiple devices on the same bus.
Pros: Even fewer pins than SPI, excellent for daisy-chaining devices, simple protocol.
Cons: Slower than SPI, with the lowest overall bandwidth. Not suitable for color TFTs.
Ideal For: Driving character LCDs or monochrome OLEDs to display lines of text. Rarely used for color TFT displays.
The Bottom Line: Perfect for command and control, not for pushing pixels.
B. High-Speed Interfaces: For Video, Animation, and Large Displays
1. Parallel RGB Interface
How it Works: Uses multiple parallel data lines (例えば, 16 または 24 bits) to transmit all color components of a single pixel in one clock cycle.
Pros: High speed, relatively simple timing, easy to debug, no licensing fees.
Cons: Very high pin count (often 20+ pins), complex PCB routing, susceptible to electromagnetic interference (EMI).
Ideal For: Medium-resolution embedded projects (例えば, 800×480 and below) where the MCU has a built-in LCD controller.
The Bottom Line: A classic, brute-force solution for medium-performance displays.
2. LVDS (低電圧差動信号伝送)
How it Works: Transmits data using differential pairs, which are highly resistant to noise and EMI.
Pros: Very high speed, excellent noise immunity, lower pin count than RGB, can support longer cables.
Cons: Requires native support from the MPU or an additional RGB-to-LVDS converter chip. More complex hardware design.
Ideal For: Medium to large-sized, high-resolution displays (例えば, 1024×768 and above). Common in industrial HMI, 自動車のダッシュボード, および医療機器. It’s the traditional standard for laptop screens.
The Bottom Line: The industrial workhorse for robust, high-resolution applications.
3. MIPI DSI (モバイル産業用プロセッサー インターフェイス – Display Serial Interface)
How it Works: A high-speed serial interface using differential lanes that transmits data in packets (like Ethernet or PCIe).
Pros: Extremely high speed, very low pin count (1-2 data lanes + clock), 低消費電力, excellent noise immunity.
Cons: Complex protocol, requires native MPU support, debugging requires specialized tools, potential licensing issues.
Ideal For: The dominant standard in smartphones and tablets. Now widely used in high-performance Single-Board Computers (SBCs) like Raspberry Pi and small, high-resolution displays.
The Bottom Line: The modern high-performance champion for power-efficient, dense displays.
Interface Comparison Table:
| インタフェース | Speed | Pin Count | Complexity | Typical Application |
|---|---|---|---|---|
| spi | Low | Very Low | Low | ウェアラブル, Small Devices |
| I2c | Very Low | Very Low | Low | Character LCDs, Sensors |
| パラレルRGB | Medium-High | Very High | Medium | Embedded GUI Projects |
| LVDS | High | Low | High | 自動車, 産業用, Laptops |
| MIPI DSI | Very High | Low | Very High | スマートフォン, Tablets, High-end SBCs |
Part 2: Resolution vs. サイズ – The Key to Image Clarity
It’s not just about the number of pixels; it’s about how densely they are packed.
解決: The total number of pixels on a screen, expressed as width x height (例えば, 1920×1080). This defines the amount of detail an image can hold.
サイズ: The diagonal length of the screen, measured in inches.
The Critical Link: PPI (Pixels Per Inch)
PPI connects resolution and physical size. It’s calculated as:PPI = √(Horizontal Pixels² + Vertical Pixels²) / Diagonal Screen Size (inches)
A higher PPI means a denser concentration of pixels, resulting in a sharper, more detailed image where you cannot distinguish individual pixels.
Real-World Example:
A 5-inch 1920×1080 screen has a PPI of ~440.
A 10-inch 1920×1080 screen has a PPI of ~220.
Both show the same content, but the 5-inch screen will look incredibly sharp, while the 10-inch screen will appear noticeably pixelated (“pixel-dense” vs. “blocky”).
Choosing the Right Combination:
Close-up viewing (smartwatches, handheld devices): Aim for a high PPI (>300).
Arm’s length viewing (control panels, smart home hubs): 200-300 PPI is a good sweet spot.
Distant viewing (car infotainment, kiosks): You can opt for a lower PPI.
Part 3: Other Crucial Parameters to Consider
色の濃さ: The number of bits used to represent the color of a single pixel.
RGB565 (16-少し): Good enough for many basic UIs. May show color banding in gradients.
RGB888 (24-少し “True Color”): Displays 16.7 百万色. Essential for photorealistic images and smooth color transitions. This is the modern standard.
ドライバーIC (Integrated Circuit): Every display module has a driver chip (例えば, ILI9341, ST7789). Ensure your platform has readily available libraries (like Arduino’s TFT_eSPI, or LVGL’s built-in drivers) to avoid writing complex initialization code from scratch.
Your Practical Selection Checklist
Define Your Need: What will it display? Static text, a complex GUI, or video? What’s the physical size and viewing distance?
Check Your Main Controller: What interfaces does your MCU/MPU support natively? Does it have enough memory and processing power to handle your target resolution?
Filter by Interface:
Tiny screen, basic graphics? -> spi
Medium screen, interactive GUI? -> パラレルRGB
High-res, large, or power-sensitive screen? -> MIPI DSI または LVDS
Match Resolution & サイズ: Use the PPI calculation to ensure your chosen screen is sharp enough for its purpose.
Verify the Details: Check the voltage (3.3V vs. 5V), backlight type, connector type (FPC), and whether you need a touchscreen (resistive/capacitive).
By following this structured approach, you can cut through the noise and confidently select the perfect LCD display that brings your project to life without becoming a development bottleneck.
What display challenges have you faced in your projects? Share your experiences in the comments below!
