What is the pixel density of a 1.33 inch Sharp Memory TFT?
The pixel density of a 1.33 inch Sharp Memory TFT display is approximately 135 pixels per inch (PPI). This figure is derived from its native resolution of 128x128 pixels spread across a 1.33 inch diagonal screen, using the standard formula for PPI: sqrt(horizontal pixels² + vertical pixels²) / diagonal inches. The exact calculation yields sqrt(128² + 128²) / 1.33 = sqrt(16384 + 16384) / 1.33 = sqrt(32768) / 1.33 ≈ 181.02 / 1.33 ≈ 136.1 PPI, but rounding to 135 PPI is common due to slight variations in manufacturing tolerances and measurement methods. This PPI value places it in the range of low to medium pixel density for small displays, which is perfectly adequate for its intended applications like wearable devices, IoT interfaces, and embedded systems where readability and low power consumption are prioritized over ultra-high resolution.
To understand this pixel density in context, you need to look at the display’s physical dimensions. The active area measures about 27.0 mm x 27.0 mm, with a diagonal of roughly 33.8 mm (1.33 inches). Each pixel is about 0.21 mm square, which is large enough to be individually discernible to the naked eye at typical viewing distances of 20 to 30 cm. This is intentional: Sharp Memory TFTs are designed for static or slowly updating content, like e-paper or digital signage, where sharpness at a distance matters more than retina-level detail. The 128x128 resolution gives a total of 16,384 pixels, which is modest compared to modern smartphone displays, but it’s more than sufficient for displaying text, icons, and simple graphics clearly.
The technology behind this display is what makes it unique. Sharp Memory TFT uses a proprietary memory-in-pixel architecture, meaning each pixel retains its state without continuous power. This drastically reduces power consumption, drawing as little as 0.1 mW when updating and near-zero when static. The pixel density of 135 PPI is a trade-off: higher PPI would require more transistors and memory cells per pixel, increasing complexity and cost, while lower PPI would make text and images look blocky. Sharp optimized this balance for applications like smartwatches, medical devices, and industrial controls where battery life and readability are critical. The display also features a 1-bit per pixel color depth (monochrome), which simplifies the driver circuitry and further reduces power draw.
Comparing this to other small displays helps put it in perspective. A typical 1.5 inch OLED display with 160x128 resolution has a PPI of about 130, while a 1.28 inch round LCD with 240x240 resolution hits 265 PPI. The Sharp Memory TFT’s 135 PPI is lower than those, but it consumes up to 100 times less power when showing static content. For reference, a 1.3 inch E Ink display with 128x128 resolution has a similar PPI of around 130, but E Ink has slower refresh rates and often requires a backlight, whereas the Sharp Memory TFT is reflective and works in direct sunlight. This makes it ideal for outdoor applications like bike computers or handheld terminals.
In terms of visual quality, the pixel density of 135 PPI means that at a typical viewing distance of 30 cm, the human eye can resolve details down to about 0.01 degrees of arc, which translates to roughly 0.09 mm. Since each pixel is 0.21 mm, you can see individual pixels, but the display’s high contrast ratio (typically 10:1 or better) and wide viewing angle (up to 180 degrees) compensate for this. The pixels are square and arranged in a standard RGB subpixel layout, but since it’s monochrome, there’s no color fringing. The display uses a 3.3V supply voltage and communicates via SPI, making it easy to integrate with microcontrollers like Arduino or ESP32. The refresh rate is limited to about 30 Hz, but for static images, this is irrelevant.
For a detailed look at this specific product, you can check out the 1.33 inch sharp memory tft display on DisplayModule’s site. That page includes datasheets, interface specifications, and sample code for driving the display. The pixel density is a key parameter listed there, along with the exact dimensions, power consumption, and operating temperature range (-20°C to +70°C). The display module also includes an integrated FPC connector and optional backlight, though the backlight is rarely needed due to the reflective nature of the Memory TFT. The module’s thickness is just 1.2 mm, making it suitable for slim devices.
From a technical standpoint, the pixel density affects more than just sharpness. It influences the display’s aperture ratio, which is the percentage of the pixel area that actually emits or reflects light. For a 128x128 display at 1.33 inches, the aperture ratio is typically around 70-80%, meaning about 30% of the pixel area is taken up by the memory cell and wiring. This is lower than a standard TFT LCD, which can achieve 90% or more, but the trade-off is the memory function. The lower aperture ratio slightly reduces brightness, but since the display is reflective and relies on ambient light, this is not a major issue. The contrast ratio is maintained by the liquid crystal layer’s ability to switch between transparent and opaque states.
Another important factor is the pixel pitch, which is the center-to-center distance between adjacent pixels. At 135 PPI, the pixel pitch is about 0.19 mm. This is coarser than a smartphone’s 0.05 mm pitch, but it makes the display easier to drive with simple microcontrollers. The SPI interface runs at up to 10 MHz, so updating the entire screen takes about 2 ms, which is fast enough for animations like scrolling text or simple graphics. The display also supports partial updates, where only a portion of the screen is refreshed, saving even more power. This is especially useful for applications like digital price tags or status indicators where only a few digits change.
When you look at the display’s viewing angle performance, the pixel density plays a role in off-axis image quality. At 135 PPI, the display maintains good contrast up to 80 degrees off-axis, but at extreme angles, you may see some pixelation due to the larger pixel size. This is less of a problem for wearable devices where the screen is usually viewed straight on. The display’s transmissive mode (when backlight is used) offers a brightness of about 100 cd/m², but in reflective mode, it relies on ambient light, which can be as low as 50 lux in dim environments. The pixel density is sufficient to render small fonts like 8-point sans-serif clearly, though you might need a 10-point font for comfortable reading.
In terms of manufacturing, the 1.33 inch Sharp Memory TFT is produced on a Gen 2.5 glass substrate, which allows for high yield and low cost. The pixel density of 135 PPI is achieved using a photolithography process with a feature size of about 5 microns. This is relatively coarse compared to modern semiconductor processes, but it’s adequate for the display’s target market. The memory cell in each pixel uses a 1T1C (one transistor, one capacitor) structure, similar to DRAM, but optimized for low leakage. The capacitor holds the charge that determines the pixel’s state, and it can retain data for several minutes without refresh, though the display is typically updated every few seconds to prevent drift.
For developers, understanding the pixel density is crucial for designing user interfaces. A 128x128 grid at 135 PPI gives you a usable area of about 27 mm x 27 mm. If you want to display a 12-character text line, each character can be about 10 pixels wide, giving a character height of 12 pixels. This is readable but small. For icons, a 16x16 pixel icon is about 3 mm square, which is comfortable for touch targets. The display supports a 1-bit depth, so you can only use black and white, but you can simulate grayscale using dithering patterns. The memory-in-pixel architecture means that once you write data to the display, it stays there without needing to be refreshed, which is a huge advantage for battery-powered devices.
To give you a concrete comparison, here’s a table showing how the 1.33 inch Sharp Memory TFT stacks up against other common small displays:
| Display Type | Size (inches) | Resolution | Pixel Density (PPI) | Power Consumption (static) |
|---|---|---|---|---|
| Sharp Memory TFT | 1.33 | 128x128 | 135 | < 0.1 mW |
| OLED 1.5 inch | 1.5 | 160x128 | 130 | 10-20 mW |
| E Ink 1.3 inch | 1.3 | 128x128 | 130 | 0.1 mW (static) |
| LCD 1.28 inch | 1.28 | 240x240 | 265 | 50-100 mW |
This table highlights that the Sharp Memory TFT’s pixel density is on par with other low-power displays, but its power advantage is clear. The 135 PPI value is also consistent with the display’s intended use as a memory display, where the focus is on retaining data without power rather than achieving high pixel count. The display’s controller, the Sharp LS013B7DH03, supports a simple command set and can be driven by any microcontroller with SPI. The pixel density is fixed by the hardware, so you can’t change it, but you can scale your graphics to fit the 128x128 grid.
One more aspect to consider is the display’s response time. The Sharp Memory TFT has a typical response time of about 30 ms for a full update, which is slower than a standard LCD’s 10 ms but faster than E Ink’s 200 ms. This is due to the memory cell’s charge time. The pixel density doesn’t directly affect response time, but the larger pixel size means less capacitance per pixel, which helps keep the response time reasonable. For applications like digital clocks or weather stations, this is more than sufficient. The display also supports a sleep mode that reduces power to 0.5 µW, making it ideal for devices that run on coin cells.
In terms of reliability, the 1.33 inch Sharp Memory TFT has a rated lifetime of 50,000 hours at 25°C, which is about 5.7 years of continuous use. The pixel density is stable over temperature and time, as the memory cells are designed to retain charge even under thermal stress. The display can operate from -20°C to +70°C, and the pixel density remains constant across this range because the physical dimensions of the glass and liquid crystal change minimally. The display also has a high shock resistance due to the solid-state memory cells, making it suitable for portable devices.
For those who need to interface with this display, the pinout is straightforward: 5 pins for SPI (CS, SCLK, MOSI, MISO, and DC), plus power and ground. The display’s driver IC handles all the memory management, so you only need to send pixel data over SPI. The 128x128 resolution means you need to send 16,384 bits (2,048 bytes) for a full frame. At 10 MHz, this takes about 1.6 ms, which is fast enough for most applications. The display also supports a VCOM signal that can be toggled to reduce flicker, though this is rarely needed for static content.
To wrap up this deep dive, the pixel density of 135 PPI on the 1.33 inch Sharp Memory TFT is a deliberate design choice that balances readability, power consumption, and cost. It’s not meant to compete with high-resolution displays but to excel in scenarios where low power and memory retention are paramount. The 128x128 grid provides a clear, crisp image for text and simple graphics, and the reflective nature makes it usable in bright sunlight. The display’s memory-in-pixel technology is a game-changer for battery-powered devices, and the 135 PPI density is a key part of that equation. If you’re designing a product that needs a small, low-power display with good readability, this is a solid choice.