A TFT (Thin Film Transistor) display is a type of LCD (Liquid Crystal Display) that utilizes thin film transistor technology to control individual pixels (actively controlled). This provides higher image quality and faster refresh rates compared to traditional passive-matrix displays. Most modern computer displays today use IPS TFT technology.
| Display Technology | Remark |
|---|---|
| LCD | Text only, cheap, for outdoors |
| TFT | High resolution color graphics, cheap, readily available in almost any size, for indoors |
| IPS TFT | In-Plane Switching: advanced TFT technology for superior viewing angles and better color reproduction |
| OLED | Very expensive, only very small and monochrome OLEDs are affordable |
Overview
A usable TFT display consists of two main components:
- Display: The actual display unit, which can vary in form, pixel density, TFT technology, and shape.
- Controller: A chip that drives the display and acts as an interface between the display and a microcontroller.
While you can purchase these separately, it’s more common to buy a ready-to-use breakout board that integrates both on a single PCB.
Display Controller
There are far more displays than display controllers. For example, the popular ST7789 is a widely used TFT display controller capable of driving most TFT displays with a maximum resolution of 240x320 at 262K colors (18-bit).
The display controller provides the interfaces that microcontrollers use to communicate with the display. When purchasing a breakout board, most designs expose only the pins for the SPI interface.
SPI Interface
Most TFT display controllers support the fast SPI interface, which is a serial interface where data is transmitted bit by bit, requiring only a few (typically three) wires. Modern microcontrollers, such as the ESP32, are fast enough to support even high frame rates over this interface.
Parallel Interface
Some controllers also support a Parallel interface, where multiple bits are transmitted simultaneously. Parallel interfaces come in 8-bit and 16-bit variants, and the more bits transferred at once, the faster the data transfer rate.
Parallel interfaces are significantly faster than SPI, enabling smoother and faster display refresh rates, especially on larger or high-resolution displays. These are well-suited for complex graphics or real-time applications like video playback.
However, the downside is the high number of GPIOs required and more complex wiring. Many microcontrollers lack the necessary GPIO pins for this interface.
For most DIY projects, implementing a Parallel interface is usually overkill. The SPI interface is sufficient for nearly all DIY use cases, as real-time high-resolution video at high frame rates is not typically what you’re aiming for with small TFT display boards.
LCD, TFT, IPS
TFT is an evolution of simple LCD displays, which is why you might come across the term TFT LCD.
TFT LCD
While TFT LCDs offer faster response times and better color contrasts compared to older matrix LCDs, they are still a type of LCD display that uses liquid crystals, now controlled actively rather than passively.
Basic TFT displays are very affordable today, but they do have a few limitations:
- Viewing Angle: A narrow viewing angle results in image degradation when viewed from the side.
- Low Color Accuracy: Color and contrast are limited, with colors potentially appearing faded.
IPS
IPS (In-Plane Switching) is an advanced type of TFT LCD that, while slightly more expensive, improves on many of the limitations of standard TFTs by offering better liquid crystal alignment. IPS displays are also more durable but tend to have slower response rates compared to other technologies.
- Wide Viewing Angle: IPS screens maintain color accuracy and contrast even when viewed from extreme angles. This feature is sometimes referred to as Full Angle.
- Better Color: IPS displays offer more vivid colors and stronger contrasts compared to standard TFTs.
Power Consumption
The improvements in display quality come with an increase in power consumption:
- TFT displays generally consume more power compared to older LCDs due to their active control mechanism.
- IPS displays consume more power than standard TFTs due to the enhanced crystal alignment and the additional backlight needed for better color accuracy and viewing angles.
Use Cases
Depending on your use case, TFT displays are often the most cost-effective choice, but they are not always the best option:
- Battery-Operated Devices: If power consumption is a concern, consider LCD, OLED, or ePaper displays. You could also opt for simpler, low-power LEDs with just a few µA current consumption, or skip the display altogether.
- Display Quality: If superior display quality is your priority, you might want to explore the (more expensive) OLED displays.
- Outdoor Use: For devices used outdoors in bright sunlight, TFT is typically not suitable. ePaper is the best choice for visibility, though LCD and OLED can also work due to their high contrast ratios.
- Fast Refresh Rates: If high refresh rates are crucial (e.g., for real-time displays or gaming), classic TFT (over IPS) is the better option. For the best combination of display quality and fast refresh rates, choose OLED.
| Feature | LCD | TFT | IPS | OLED | ePaper |
|---|---|---|---|---|---|
| Energy Efficient | +++ | ++ | + | ++ | ++++ |
| Display Quality | - | + | ++ | +++ | + |
| Sunshine-Proof | ++ | - | - | + | ++++ |
| Fast Refresh | + | +++ | ++ | ++++ | - |
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(content created Oct 16, 2024)