Ιστολόγιο περίπου How to Design with a 1.14-Inch TFT LCD? A Practical Guide for Compact Industrial Electronics

A compact display can create a surprisingly demanding engineering problem.

When an industrial product has only a few centimetres available on its front panel, the display must do more than show information. It has to fit the mechanical envelope, communicate effectively at a small viewing size, work within the processor's available resources and remain practical to manufacture.

This challenge is increasingly common in the development of portable test instruments, wearable industrial devices, compact controllers, smart sensors and space-constrained embedded systems.

For these applications, a 1.14-inch TFT LCD can provide a useful balance between colour graphics, physical size and embedded-system integration.

The SFTO114JY-7422AN is one such module. It combines a 135 × 240 RGB resolution, an ST7789V display driver, a four-line SPI interface and a typical luminance of 400 cd/m² within a module measuring just 17.6 × 31.0 × 1.6 mm.

But the important engineering question is not simply whether the display fits.

It is whether the available pixels, optical characteristics, electrical interface and mechanical structure can support the intended product.

This article examines those questions from the perspective of an OEM hardware engineer developing a compact industrial device.

1. Start with the information architecture, not the display diagonal

A 1.14-inch display has an active area of only 14.864 × 24.912 mm. That is a relatively small space in which to communicate measurements, operating conditions, warnings and user instructions.

The first design decision should therefore be about information hierarchy.

A common mistake in miniature HMI development is to reproduce a larger product's interface on a smaller screen. The result is usually an overcrowded layout, small text and too many competing visual elements.

A more effective approach is to determine which information the operator needs immediately and which information can be accessed through a secondary screen.

For example, consider a portable industrial measurement instrument. Its main screen might contain:

• One prominent measurement value.

• A clearly identified measurement unit.

• A compact operating-status indicator.

• A battery or connection symbol.

• One or two essential navigation options.

Configuration parameters, historical readings and detailed diagnostic information can be placed on secondary screens.

This approach makes better use of the 135 × 240 pixel format.

What does 135 × 240 resolution actually provide?

The SFTO114JY-7422AN uses a vertical RGB pixel arrangement with 135 horizontal pixels and 240 vertical pixels.

The total number of addressable pixels is:

135 × 240 = 32,400 pixels.

This is sufficient for a compact graphical interface, provided that the software is designed around the physical display area rather than an assumed desktop-style layout.

The active-area dimensions also provide a useful reference for UI design:

• Horizontal active area: 14.864 mm.

• Vertical active area: 24.912 mm.

• Horizontal pixel pitch: 0.1101 mm.

• Vertical pixel pitch: 0.1038 mm.

The resulting pixel density is approximately 242 pixels per inch, calculated from the diagonal pixel count and the specified 1.14-inch diagonal.

This relatively high pixel density allows the module to display compact graphics and fine interface details. However, high pixel density does not automatically guarantee readable text.

Font selection should be based on the physical character height, stroke thickness, viewing distance and expected user conditions.

For an industrial instrument, it is generally better to use fewer readable characters than to display every available parameter in very small text.

Design recommendation: Develop the primary screen at the actual 135 × 240 resolution and inspect it at approximately the intended viewing distance. Do not rely exclusively on enlarged screenshots displayed on a computer monitor.

2. The normally black display mode: What does it mean for HMI design?

The SFTO114JY-7422AN specifies a normally black TFT display mode.

In a normally black configuration, the dark state is the default optical state when the relevant pixel is not driven to transmit light. This makes dark-background graphical interfaces a natural option to evaluate.

For example, an interface could use:

• A dark background for the main screen.

• Bright numerical characters for measurements.

• Contrasting colours for warning and status indicators.

• Consistent icon shapes for navigation.

There are practical advantages to this approach in a small display.

Bright information can be visually separated from less important interface elements, helping the operator identify the main measurement without reading every item on the screen.

However, normally black should not be interpreted as a guarantee that a dark user interface will consume less power. The actual power demand depends on the panel, display content, backlight settings and driver architecture.

Similarly, a dark background does not eliminate the need to test the interface under bright ambient lighting.

The SFTO114JY-7422AN specifies a typical brightness of 400 cd/m², but outdoor suitability depends on the complete optical system, including the front cover and any touchscreen added later.

The most useful evaluation is to compare actual interface designs under the lighting conditions expected in the finished product.

3. Can a four-line SPI display work efficiently with a low-cost microcontroller?

For a compact industrial device, the display interface affects much more than the connector pin count.

It influences PCB routing, firmware complexity, processor workload and screen update performance.

The SFTO114JY-7422AN uses a four-line SPI interface and the ST7789V display driver IC.

The module's FPC interface provides the following principal signals:

This is a straightforward interface architecture for many embedded microcontroller platforms.

A four-line SPI configuration is particularly useful when the host processor has limited general-purpose I/O pins or when PCB routing space is restricted.

However, there is an important distinction between interface simplicity and data-transfer performance.

Calculate the screen update budget before selecting the MCU

A full-screen image contains:

135 × 240 = 32,400 pixels.

If the firmware transfers each pixel using 16-bit RGB565 data, the total image payload is:

32,400 × 16 = 518,400 bits.

The theoretical transfer time at an illustrative SPI clock of 10 MHz is:

518,400 ÷ 10,000,000 = 51.84 ms.

This corresponds to approximately 19.3 complete screen transfers per second, before command overhead, software delays and other implementation limitations.

At 20 MHz, the theoretical payload transfer time becomes approximately 25.92 ms.

These figures are calculations, not guaranteed performance specifications for the SFTO114JY-7422AN. The actual SPI operating limit must be confirmed against the complete module and controller timing requirements.

The calculation nevertheless illustrates an important point: not every industrial interface needs continuous full-screen refresh.

A measurement instrument that changes only a few numerical values can update the corresponding screen regions rather than redraw all 32,400 pixels.

Use partial updates to reduce unnecessary data transfer

For a typical embedded HMI, a useful firmware strategy is to divide the interface into independent regions.

For example:

• Measurement region: refreshed when the measured value changes.

• Battery region: refreshed only when battery status changes.

• Communication indicator: refreshed when connection status changes.

• Menu region: refreshed when the operator changes screens.

This can reduce unnecessary SPI traffic and processor activity.

The ST7789V controller documentation describes on-chip display RAM and partial-display functionality. These controller capabilities can be useful when designing efficient graphical interfaces.

Nevertheless, the actual memory configuration, address window, pixel mapping and initialization sequence must be verified for this specific 135 × 240 module.

A controller's general capabilities should never be assumed to represent every feature enabled in a particular display module.

For engineering teams, the practical recommendation is to validate the complete initialization code, screen orientation, colour order and update behaviour using the actual module sample before freezing the firmware architecture.

4. Power budgeting: The backlight is only part of the calculation

Battery-powered industrial equipment often has a strict energy budget.

A compact display may operate for extended periods in a handheld instrument, portable sensor or field-service device. Its power demand should therefore be included in the product's total power model from the beginning.

The SFTO114JY-7422AN uses a single white LED backlight. Its specified electrical characteristics include:

Estimate the backlight power

At the specified typical LED voltage and current:

P = V × I

P = 3.0 V × 0.020 A

P = 0.060 W

The nominal backlight power is therefore approximately 60 mW.

This is a useful starting point for battery calculations, but it is not the total display-system power.

The logic supply, processor, sensor circuits, communication modules and power-conversion losses must also be considered.

For example, an instrument that operates its display continuously for eight hours will have a different energy profile from one that activates the screen only when the operator presses a button.

Implement a controlled backlight strategy

A practical approach is to provide firmware-controlled brightness management.

Possible operating modes include:

Normal operation: Use a brightness setting appropriate for the usual indoor environment.

Power-saving operation: Reduce backlight output when the equipment remains idle.

Active interaction: Restore the selected brightness when the user interacts with the instrument.

Sleep mode: Disable unnecessary display activity when the equipment is not being used.

The datasheet also specifies low-current sleep-in conditions:

• VDD sleep current: 15 µA typical, 30 µA maximum.

• VDDIO sleep current: 5 µA typical, 10 µA maximum.

These figures are useful when estimating standby consumption, but the total system standby current must also include the microcontroller, regulators and other powered circuits.

An important engineering distinction is that the module's sleep current specifications do not automatically represent the complete battery consumption of the finished product.

5. Optical performance: How should engineers interpret 400 cd/m² and 800:1?

The SFTO114JY-7422AN specifies a typical luminance of 400 cd/m².

Its optical characteristics also list:

These values should be considered together rather than treated as independent marketing figures.

Brightness does not determine every aspect of visibility

A 400 cd/m² display may be suitable for many indoor industrial applications, but the finished product's readability also depends on:

• Ambient illumination.

• Surface reflections.

• Front-cover material.

• Viewing distance.

• Viewing angle.

• Display colour combinations.

• Optical losses from additional layers.

For example, placing a touchscreen cover lens over the original LCD may change the optical characteristics of the complete assembly.

An anti-glare surface treatment may also change the perceived sharpness or contrast.

This is why the final optical evaluation should be carried out using the complete front assembly.

Understanding the 4.8% transmittance figure

The datasheet specifies 4.8% transmittance with polarizer.

This is an optical transmission characteristic and should not be confused with the 400 cd/m² backlight luminance.

It also should not be used by itself to calculate the final display brightness without knowing the measurement conditions and optical structure.

If the project requires additional cover glass or a capacitive touch sensor, the resulting optical stack should be measured as an assembly.

Is an 80-degree viewing angle sufficient?

The specification identifies an All View viewing direction and gives 80-degree values in four viewing directions.

This is useful when considering how the display will be mounted in a handheld or fixed industrial product.

However, engineers should confirm the precise angular measurement convention and contrast-ratio threshold before treating the value as a guaranteed viewing cone.

A useful prototype test is to evaluate the actual screen from the left, right, top and bottom at the intended operating distance.

This is particularly important for equipment that may be mounted at an angle or used while being held in one hand.

6. Mechanical integration: Why a 1.6 mm profile deserves attention

In compact industrial electronics, mechanical dimensions can be as important as optical specifications.

The SFTO114JY-7422AN has the following physical characteristics:

A 1.6 mm module thickness can be attractive when designing thin portable electronics or compact control units.

It gives the mechanical engineer a useful starting point for arranging the display, PCB, battery and enclosure.

However, the final product thickness cannot be calculated by simply using the LCD module thickness.

The design must also account for:

• Front cover or protective lens.

• Adhesive layers.

• Mounting supports.

• FPC bending and connector clearance.

• PCB thickness.

• Housing tolerances.

• Any additional touchscreen assembly.

FPC routing deserves early attention

The module uses an FPC connector for its electronic interface.

The flex cable should be routed without excessive bending, twisting or mechanical tension.

The enclosure should also prevent the display glass from being subjected to unnecessary pressure during assembly.

The datasheet specifically warns that excessive pressure on the display surface or adjoining areas may cause colour variation.

This is especially relevant when designing a small front-panel opening, where mechanical tolerances can concentrate force around the display edges.

A recommended development sequence is:

1. Obtain the module mechanical drawing.

2. Define the display mounting datum.

3. Position the FPC connector and routing path.

4. Establish the cover-lens opening.

5. Check the mechanical tolerance stack.

6. Validate the assembled structure using physical samples.

The final housing should be evaluated with the actual display module installed, not only through a CAD model.

7. Adding capacitive touch: How can a miniature LCD become a modern HMI?

A compact colour display does not necessarily need to remain a button-operated interface.

Many industrial product developers are moving towards touch-based operation to simplify front-panel design and provide more flexible menu navigation.

A capacitive touchscreen can be considered for applications such as:

• Compact industrial controllers.

• Portable diagnostic equipment.

• Smart measuring instruments.

• Wearable industrial terminals.

• Miniature monitoring systems.

• IoT devices requiring local user interaction.

The SFTO114JY-7422AN datasheet does not specify an integrated capacitive touchscreen.

However, a compatible CTP solution can be evaluated as an additional customized assembly.

What needs to be considered before adding CTP?

The small physical dimensions make touch integration particularly sensitive to mechanical and optical details.

Cover lens geometry

The cover lens must match the housing opening and provide an appropriate touch area.

Touch active area

The touch-sensitive area should align with the usable display region. Engineers should avoid creating unnecessarily narrow touch targets.

Touch controller

The selected controller must be compatible with the host processor and its available communication resources.

FPC routing

The touch FPC and display FPC must be accommodated without interfering with the enclosure or PCB.

Optical performance

The added sensor, cover glass and adhesive may affect reflections, transmission and perceived contrast.

Operating conditions

If the equipment is expected to be used with gloves, moisture or in a demanding industrial environment, the touch solution should be evaluated under those actual conditions.

Standard and customized CTP options

Saef Technology Limited can provide standard capacitive touchscreen options or discuss customized CTP development according to the customer's product structure, cover-lens design, electrical interface and functional requirements.

For a 1.14-inch TFT LCD application, the best approach is to evaluate the display and touch panel together rather than treating them as unrelated components.

This allows the engineering team to coordinate the front-panel dimensions, optical stack, FPC position and touch-controller architecture before PCB and enclosure designs are finalized.

A small display can still support a sophisticated HMI, but the touch targets, menus and interaction flow must be designed specifically for its physical size.

8. Temperature and reliability: What does the datasheet actually establish?

Industrial equipment is often expected to operate beyond the comfortable conditions of a typical office environment.

The SFTO114JY-7422AN specifies:

• Operating temperature: -20°C to +70°C.

• Storage temperature: -30°C to +80°C.

This makes the module a candidate for a range of industrial and portable electronic applications.

However, the temperature rating should not be interpreted as a guarantee that every optical parameter remains unchanged across the complete range.

Engineers should verify the display's startup, contrast, brightness, response behaviour and touch performance under the conditions expected in the finished product.

Environmental testing listed in the datasheet

The module specification includes the following reliability tests:

One important qualification is stated in the datasheet: these reliability tests are conducted with the module unpowered.

Consequently, they should not be interpreted as proof of continuous functional operation under every listed environmental condition.

For an OEM qualification programme, the finished equipment should undergo its own environmental testing.

IEC 60068-2-14 provides a recognized reference for temperature-change testing, while IEC 60068-2-78 addresses damp-heat testing under steady-state conditions.

For ESD immunity, IEC 61000-4-2 provides a useful reference for product-level test planning.

The actual test levels and acceptance criteria should be selected according to the intended product category and market requirements.

A display module's reliability test results do not automatically establish the compliance of the complete industrial instrument.

9. A design verification checklist before ordering production quantities

Before committing to the SFTO114JY-7422AN for a new product, engineering teams should complete a practical design review.

Display and UI

• Confirm that 135 × 240 resolution is sufficient.

• Check font sizes at the actual viewing distance.

• Verify screen orientation and RGB/BGR colour order.

• Evaluate the interface under expected lighting conditions.

Electrical

• Confirm the 2.8 V typical logic supply architecture.

• Check the 1.8 V typical I/O supply and MCU logic compatibility.

• Verify SPI clock timing and signal integrity.

• Validate reset and initialization sequences.

• Design an appropriate LED backlight drive circuit.

Firmware

• Test the ST7789V initialization sequence.

• Confirm the address window and pixel mapping.

• Evaluate full-screen and partial-screen updates.

• Measure real-world refresh performance.

• Implement suitable sleep and wake-up behaviour.

Mechanical

• Verify the 17.6 × 31.0 × 1.6 mm module envelope.

• Check FPC orientation and connector access.

• Review cover-lens and housing tolerances.

• Prevent excessive mechanical pressure on the LCD.

Touchscreen, if required

• Confirm the CTP active area.

• Select a compatible touch controller.

• Verify the touch interface and FPC arrangement.

• Evaluate optical performance after assembly.

• Test touch operation under the intended conditions.

This checklist is particularly useful before PCB release and enclosure tooling, when design changes are still relatively inexpensive.

10. Is this 1.14-inch TFT LCD the right choice for your next embedded product?

The SFTO114JY-7422AN is not intended to replace larger displays in applications that need extensive menus, complex graphics or long text descriptions.

Its value is in applications where the available front-panel area is limited and the interface can be designed around a focused set of information.

Potential applications include:

Portable test and measurement instruments

Compact electrical testers, diagnostic tools and handheld measurement equipment.

Industrial sensor terminals

Local displays for sensor readings, operating status and parameter settings.

Wearable industrial electronics

Compact equipment that needs a lightweight graphical interface.

Miniature control systems

Small embedded controllers where physical buttons and screen dimensions must be carefully balanced.

Smart monitoring devices

Portable monitoring products requiring colour indicators, numerical information and basic user interaction.

The suitability of each application should be established through mechanical, optical and electrical validation.

Work with a display configuration that matches your product

For an industrial display project, selecting the correct screen is only the first step.

The display must also work with the processor, power architecture, enclosure, firmware and user-interface requirements.

Saef Technology Limited supports industrial TFT LCD selection and customized display solutions, including standard and customized capacitive touchscreen integration.

For the SFTO114JY-7422AN, customers can evaluate the existing 135 × 240 display configuration or discuss whether a customized CTP assembly is appropriate for their application.

If your engineering team is developing a compact industrial instrument, wearable device or miniature HMI, share your mechanical drawing, interface requirements and expected operating conditions for a more application-focused technical discussion.

Request the SFTO114JY-7422AN Datasheet.pdf and discuss your display integration requirements.

What is the resolution of the SFTO114JY-7422AN?

The module has a 135 × 240 RGB resolution, providing 32,400 addressable pixels.

Which display driver does this 1.14-inch TFT LCD use?

It uses the ST7789V TFT display driver IC.

Does the module support SPI?

Yes. It uses a four-line SPI interface with SDA, SCL, RS, CS and RESET signals.

What is its typical brightness?

The datasheet specifies 400 cd/m² typical luminance, with the model characteristics listing 350–400 cd/m².

Can this 1.14-inch TFT LCD operate in industrial temperature environments?

Its specified operating temperature is -20°C to +70°C, and its storage temperature is -30°C to +80°C.

Does the module include a capacitive touchscreen?

The standard datasheet does not specify an integrated CTP. A compatible capacitive touchscreen can be evaluated and customized separately according to the product's mechanical and functional requirements.

Is the module suitable for battery-powered products?

Its single-LED backlight has a specified current of 20 mA. The datasheet also provides sleep-in current characteristics. Actual battery life depends on the backlight operating strategy and the complete system's power consumption.

Final engineering perspective

The most important consideration when choosing a 1.14-inch TFT LCD is not how many specifications appear on its datasheet. It is how effectively the available display area can support the product's real operating requirements.

The SFTO114JY-7422AN combines a compact 17.6 × 31.0 × 1.6 mm mechanical envelope, 135 × 240 resolution, ST7789V control, four-line SPI communication and 400 cd/m² typical brightness.

For engineers developing compact embedded equipment, it provides a practical starting point for a focused graphical interface.

The next step is to validate the module within the actual electronics, enclosure and user-interface design, and to determine whether a customized capacitive touchscreen would improve the finished product.

Contact us to discuss your next compact TFT LCD or integrated HMI project.