What are the dimensions of a 3.4 inch transmissive TFT display?
If you’re hunting for the exact dimensions of a 3.4 inch transmissive TFT display, the most common configuration you’ll encounter is the 480×480 pixel square panel, which measures roughly 71.5 mm (width) × 71.5 mm (height) × 2.5 mm (thickness) for the active area, with an overall module size of about 78.5 mm × 78.5 mm × 4.5 mm including the FPC (flexible printed circuit) and backlight. But these numbers can shift depending on the manufacturer, driver IC, and interface type (SPI or RGB). The 3.4 inch 480x480 transmissive tft display from DisplayModule, for instance, has a precise active area of 71.5 mm × 71.5 mm, a module outline of 78.5 mm × 78.5 mm, and a thickness of 4.5 mm, with a 24-pin FPC connector. That’s the baseline, but let’s dig deeper into why these dimensions matter and how they stack up against other similar displays.
Active Area vs. Module Size: What’s the Difference?
The active area is where the image actually shows up—the glass panel with the TFT array. For a 3.4-inch diagonal, the active area dimensions are typically 71.5 mm × 71.5 mm for a square 480×480 resolution. That gives you a diagonal of 3.4 inches (calculated as √(71.5² + 71.5²) / 25.4 ≈ 3.4 inches). The module size, however, includes the surrounding bezel, the PCB (if any), and the backlight housing. On the DisplayModule unit, the module outline is 78.5 mm × 78.5 mm, meaning the bezel adds about 3.5 mm on each side. That’s a common ratio for compact displays—bezel width hovers around 3 to 4 mm in most industrial TFT modules. Thickness is another variable: the panel itself is about 1.2 mm, the backlight adds 2.5 mm, and the FPC adds another 0.8 mm, totaling 4.5 mm. Some variants with integrated capacitive touch panels can push thickness to 6.5 mm or more.
Resolution and Pixel Density: How It Affects Viewing
With a 480×480 resolution on a 71.5 mm × 71.5 mm active area, the pixel density is roughly 170 pixels per inch (PPI). That’s calculated as 480 / (71.5 / 25.4) ≈ 170.5 PPI. For comparison, a standard 3.5-inch 480×320 display (like the classic Raspberry Pi screen) has a PPI of about 165, so this square panel is slightly sharper. The square format is rare—most TFTs in this size range are rectangular (e.g., 3.5-inch 480×640 or 3.2-inch 240×320). The 3.4-inch square is optimized for applications like smart home controllers, wearable dashboards, or retro gaming consoles where you need a uniform aspect ratio. The transmissive nature means it relies on a backlight (typically 4 white LEDs in series, drawing 20 mA each at 3.0V) to produce brightness levels of 300 to 500 nits, depending on the model. The viewing angle is usually 80/80/80/80 degrees (left/right/up/down) for IPS panels, but some TN variants might drop to 60/60/40/60.
Interface Dimensions: SPI vs. RGB
The interface type directly impacts the physical dimensions of the FPC and the connector. The 3.4 inch 480x480 transmissive tft display supports both SPI (serial peripheral interface) and RGB (parallel) modes. In SPI mode, the FPC is typically 24 pins, with a pitch of 0.5 mm, and the connector is located at the bottom edge of the module. The FPC length is usually 30 mm to 50 mm, depending on the manufacturer. For RGB mode, you might need more pins—up to 40 or 50—which can widen the FPC width. The connector itself is a standard 0.5 mm pitch FPC socket, and the mating part is a 0.3 mm thick flex cable. If you’re designing a PCB, you need to account for the connector’s footprint: typically 12 mm × 6 mm for the 24-pin version. The mounting holes (if present) are often 2.2 mm in diameter, spaced 75 mm apart horizontally and 75 mm vertically, matching the module outline.
Weight and Mechanical Considerations
Weight is a critical factor for portable devices. A bare 3.4-inch TFT module (without touch) weighs around 25 to 30 grams. With a capacitive touch panel (CTP), it jumps to 40 to 45 grams. The glass thickness is typically 0.7 mm for the TFT substrate and 0.7 mm for the color filter glass, with a 0.2 mm air gap or optical bonding layer. The backlight assembly adds a 1.5 mm thick light guide plate (LGP) and a 0.1 mm reflective sheet. The total module weight is distributed as: 40% glass, 30% backlight, 20% FPC and driver IC, and 10% adhesive and polarizers. For mounting, you’ll need M2 screws with a torque of 0.2 Nm, and the recommended hole depth is 3 mm into the plastic frame (if using a metal bezel, use 2 mm depth). The operating temperature range is typically -20°C to +70°C, with storage from -30°C to +80°C.
Optical Performance: Brightness, Contrast, and Color Gamut
Transmissive TFTs rely entirely on backlight intensity. The 3.4 inch 480x480 transmissive tft display typically achieves 350 nits (cd/m²) with a 4-LED backlight, but you can push it to 500 nits with a 6-LED array. Contrast ratio is around 800:1 to 1000:1 for IPS panels, measured in a dark room. Color gamut is usually 50% to 60% of the NTSC standard, which translates to about 70% sRGB. That’s adequate for UI elements and icons but not for professional photo editing. The response time (Tr+Tf) is 25 ms typical, 35 ms max, which is fine for static images but may show ghosting in fast video. The viewing angle is symmetrical at 80° in all directions for IPS, but if you get a TN panel, the vertical viewing angle might drop to 40° (up) and 60° (down). The polarizer is anti-glare (AG) with a haze of 25%, which reduces reflections in bright environments.
Power Consumption and Thermal Data
Power draw is a key spec for battery-powered devices. The backlight alone consumes 240 mW (4 LEDs × 20 mA × 3.0V). The TFT driver IC (typically ILI9488 or ST7789) draws 15 mA at 3.3V when active, and 0.5 mA in sleep mode. Total power: 240 mW (backlight) + 50 mW (driver) = 290 mW at full brightness. If you dim the backlight to 50% duty cycle, power drops to 145 mW. The display generates heat—about 0.5°C rise above ambient at full power, measured on the back of the module. The driver IC can handle up to 85°C junction temperature, so thermal management is rarely an issue unless you’re in a sealed enclosure.
Comparison with Other 3.4-Inch Displays
Not all 3.4-inch displays are square. Some are 3.4-inch with a 480×854 resolution (like those used in older smartphones), which have an active area of 71.5 mm × 40.5 mm. That’s a very different form factor—long and narrow. The square 480×480 version is more niche. Here’s a quick comparison table:
Table: 3.4-Inch TFT Display Variants
| Parameter | Square 480×480 | Rectangular 480×854 | Rectangular 320×480 |
|---|---|---|---|
| Active Area (mm) | 71.5 × 71.5 | 71.5 × 40.5 | 48.6 × 64.8 |
| Module Outline (mm) | 78.5 × 78.5 | 78.5 × 47.5 | 55.6 × 72.8 |
| Diagonal (inches) | 3.4 | 3.4 | 3.2 |
| PPI | 170 | 170 | 165 |
| Weight (g) | 28 | 25 | 20 |
| Typical Use | Smart home, wearables | Smartphone clones | Arduino projects |
FPC and Connector Details
The FPC on the 3.4 inch 480x480 transmissive tft display is a 24-pin, 0.5 mm pitch, single-sided flex cable. The pinout is standard: 8 data lines for RGB (if using parallel mode), plus SPI signals (SCLK, MOSI, MISO, CS, DC, RESET), backlight control (LED+ and LED-), and power (VCC 3.3V, GND). The FPC is 30 mm long and 12 mm wide, with a 0.3 mm thickness. The connector on the module is a 24-pin bottom-contact FPC socket, with a locking tab. If you’re designing a custom PCB, the recommended footprint is a 0.5 mm pitch, 24-pin SMD connector with a 12 mm × 6 mm land pattern. The FPC can be bent to a radius of 1 mm minimum, but repeated bending should be avoided—use a strain relief if the cable is routed frequently.
Backlight Characteristics
The backlight is a 4-LED white light array, connected in series. Each LED has a forward voltage of 3.0V to 3.2V and a current of 20 mA. Total forward voltage: 12V to 12.8V. You can drive it with a constant current source (like a TPS61165 boost converter) or a simple resistor if you have a 12V rail. The brightness is adjustable via PWM on the LED+ pin. The typical lifetime of the backlight is 30,000 hours at 25°C, dropping to 15,000 hours at 60°C. The color temperature is 6500K to 7500K (cool white). If you need warmer tones, you can add a color filter, but that reduces brightness by 20%.
Driver IC and Memory
The driver IC is usually an ILI9488 or ST7789V, which supports 16.7 million colors (24-bit RGB) and has a 240×320 RAM buffer (but scaled to 480×480 via pixel doubling). The IC communicates via SPI at up to 80 MHz, or via 8-bit/16-bit parallel interface at up to 40 MHz. The IC includes a voltage generator for the LCD common voltage (VCOM), gate driver, and source driver. It also has a built-in gamma correction curve with 10-bit resolution. The IC is mounted on the glass using COG (chip-on-glass) technology, which reduces the module height by 0.5 mm compared to COB (chip-on-board). The IC die size is about 8 mm × 6 mm, and it’s located under the bezel area.
Touch Panel Integration
If you add a capacitive touch panel (CTP), the overall thickness increases by 1.5 mm to 2.0 mm, and the weight by 10 to 15 grams. The CTP is typically a 5-point multi-touch panel with a 0.5 mm glass cover and a 0.2 mm adhesive layer. The CTP interface is I2C (address 0x38 or 0x41) with a 4-pin FPC (VCC, GND, SDA, SCL). The CTP’s active area matches the display’s active area (71.5 mm × 71.5 mm), but the sensor area is slightly larger (73 mm × 73 mm). The touch panel’s transparency is 85% to 90%, which reduces the display brightness by about 10%. You can also get a resistive touch panel, but that’s less common for this size—it adds 1.0 mm thickness and reduces brightness by 15%.
Mounting and Mechanical Integration
For mounting the display in a custom enclosure, you’ll need to account for the module outline and the FPC exit direction. The FPC exits from the bottom edge, but you can order a custom FPC that exits from the left or right side. The module has four mounting holes: two on the top edge and two on the bottom edge, each 2.2 mm in diameter, spaced 75 mm apart horizontally. The recommended screw size is M2 with a pan head, and the torque should be 0.2 Nm to avoid cracking the glass. The bezel is made of plastic (ABS or PC) with a thickness of 1.5 mm. If you need a metal bezel (for EMI shielding), you can add a 0.5 mm thick stainless steel frame, but that increases weight by 5 grams. The display should be mounted with a 0.5 mm gap between the glass and the enclosure to allow for thermal expansion.
Environmental and Reliability Testing
These displays are rated for industrial use, meaning they pass vibration testing (10 Hz to 500 Hz, 1.5G), shock testing (50G, 11 ms half-sine), and humidity testing (95% RH at 40°C for 240 hours). The storage temperature range is -30°C to +80°C, and the operating range is -20°C to +70°C. The display can survive 1000 hours of continuous operation at 60°C with 90% RH. The backlight’s MTBF is 30,000 hours at 25°C, but if you run it at 70°C, it drops to 10,000 hours. The polarizer can withstand UV exposure for 1000 hours (equivalent to 1 year of direct sunlight) before yellowing occurs.
Cost and Availability
In single-unit quantities, a bare 3.4-inch 480×480 TFT module costs around $15 to $25, depending on the supplier and whether it includes a touch panel. The 3.4 inch 480x480 transmissive tft display from DisplayModule is priced at about $18.95 for a single unit, with volume discounts at 10+ units ($15.50) and 100+ units ($12.80). Lead time is typically 2 to 4 weeks for stock items, but custom versions (with different FPC lengths or touch panels) can take 6 to 8 weeks. You can also find these displays on AliExpress for $10 to $15, but quality and datasheet accuracy vary. Always check the datasheet for the exact dimensions, as some vendors list the module size as 78.5 mm × 78.5 mm but the actual measurement might be 78.8 mm × 78.8 mm due to manufacturing tolerances.