Monochrome graphic LCDs are a practical middle ground between simple character displays and full-color TFT screens. They allow pixel-level control without the complexity, cost and power consumption of color displays.
This article explains how graphic LCDs work and compares two common controller families: ST7567 and ST7920.
What Is a Graphic LCD?
A graphic LCD allows direct control of individual pixels. Unlike character LCDs, which are limited to predefined characters, graphic LCDs can display:
- Custom fonts
- Icons and symbols
- Graphs and waveforms
- Simple user interfaces
Most graphic LCDs are monochrome, meaning each pixel is either on or off.
ST7567 Graphic LCD Displays
The ST7567 is a common controller used in smaller monochrome graphic LCD modules.
Typical features:
- Common resolution: 128x64 pixels
- Low power consumption
- SPI or parallel interface (depending on module)
- Good contrast for indoor use
ST7567 displays are often used in compact embedded systems where simple graphics are needed.
Advantages of ST7567
- Low power consumption
- Compact size
- Sufficient resolution for small interfaces
Limitations of ST7567
- No color support
- Limited resolution compared with TFT displays
- Requires a backlight for good visibility
ST7920 Graphic LCD Displays
The ST7920 is a popular controller used in larger monochrome graphic LCD modules.
Typical features:
- Common resolution: 128x64 pixels
- Larger display size compared with ST7567 modules
- Parallel or serial interface (often a simplified SPI-like interface)
- Built-in character and graphic modes
ST7920 displays are commonly used in industrial-style interfaces and devices such as 3D printers.
Advantages of ST7920
- Larger physical display size
- Flexible interface options
- Widely used and well supported
Limitations of ST7920
- Slower updates in serial mode
- Higher power consumption due to larger backlight
- More complex wiring in parallel mode
ST7567 vs ST7920 Comparison
| Feature | ST7567 | ST7920 |
|---|---|---|
| Typical resolution | 128x64 | 128x64 |
| Display size | Small | Larger |
| Interface | SPI or parallel | Parallel or serial |
| Power consumption | Low | Medium |
| Typical use | Compact devices | Industrial-style interfaces |
Interface Options
Both ST7567 and ST7920 displays support multiple interface modes depending on the module.
- SPI (or SPI-like) for reduced pin count
- Parallel for higher data throughput
ST7920 displays often use a simplified serial interface that looks similar to SPI but is not fully standard.
Performance and Memory
Graphic LCDs require more memory than character displays.
For a 128x64 display:
- 1024 bytes are needed for a full framebuffer
- Microcontrollers must update pixel data manually
- Partial updates are often used to improve speed
Compared with TFT displays, monochrome graphic LCDs require much less data, which makes them easier to drive on smaller microcontrollers.
Backlight and Contrast
Graphic LCDs depend on a backlight for visibility.
- Backlight brightness affects readability
- Contrast is adjustable on many modules
- Viewing angle is more limited than OLED
Unlike OLED displays, graphic LCDs are harder to read in low-light conditions without a backlight.
Typical Use Cases
- Measurement devices
- Industrial controllers
- 3D printer displays
- Embedded user interfaces
- Battery-powered devices with moderate power constraints
These displays are often chosen when graphics are needed but color is not required.
Important Practical Notes
- Most modules use 5V logic, but check before connecting
- Contrast adjustment is often required during setup
- Libraries differ between ST7567 and ST7920
- Serial modes may be slower than expected
- Backlight current can be significant
Conclusion
ST7567 and ST7920 graphic LCDs provide a practical solution for monochrome graphical displays. They are more flexible than character LCDs and simpler than color TFT displays.
ST7567 is well suited for compact, low-power designs, while ST7920 is often used for larger, more visible displays in industrial-style applications. Both are reliable choices when a project needs graphics without the complexity of full-color displays.