How to multiplex a 3.18 inch 128x64 COG LCD display?

To multiplex a 3.18 inch 128x64 COG LCD display, you need to drive the 128 columns and 64 rows using a controller like the ST7565 or equivalent, which handles the multiplexing internally by sequentially scanning rows while feeding column data. The 3.18 inch 128x64 COG LCD display, such as the one available from DisplayModule, uses a chip-on-glass (COG) design where the driver IC is bonded directly to the glass, reducing pin count and simplifying the interface. Multiplexing here means that the display’s 64 rows are divided into multiple pages, typically 8 pages of 8 rows each, and the controller activates one row at a time, cycling through all rows rapidly to create a persistent image due to persistence of vision. For a 128x64 monochrome display, the frame rate is usually set between 60 Hz and 100 Hz to avoid flicker, meaning each row gets refreshed every 10 to 16 microseconds. The ST7565 controller, common in these displays, supports a 1/64 duty cycle, which means it multiplexes all 64 rows, and you must provide a bias voltage of around 8.5V to 10V for the LCD glass, generated by an internal charge pump or external DC-DC converter. The interface is typically SPI, with a clock speed up to 10 MHz, allowing you to send 1,024 bytes per frame (128 columns x 8 pages) in about 1 millisecond, leaving plenty of time for other tasks. The physical pixel pitch is about 0.56 mm, giving a resolution of 128x64 at a 3.18 inch diagonal, which is common for industrial or embedded applications. The COG assembly uses anisotropic conductive film (ACF) to bond the IC to the glass, which reduces the number of external connections to just 20 to 30 pins, including power, ground, SPI lines, and contrast adjustment. The display’s operating temperature range is typically -20°C to +70°C, and the storage range is -30°C to +80°C, making it suitable for use in environments with moderate thermal variation. The pixel arrangement is a dot matrix, with each pixel being a twisted nematic (TN) cell that switches between on and off states based on the applied voltage, and the contrast ratio is around 5:1 to 10:1 depending on the viewing angle. The backlight, if included, is usually a white LED with a forward voltage of 3.0V to 3.2V and a current of 20 mA to 60 mA, providing a brightness of 100 to 200 cd/m². The display’s power consumption is about 5 mA to 10 mA for the LCD drive alone, with the backlight adding another 20 mA to 60 mA, so total power draw is under 100 mA at 3.3V or 5V. The multiplexing scheme requires careful timing, and the ST7565 controller has a built-in oscillator that generates the frame clock, but you can also provide an external clock if needed. The bias voltage is set by a resistor divider, and the contrast is adjusted by varying the voltage on the V0 pin, typically between 8V and 12V. The display’s response time is about 10 ms to 20 ms for turn-on and 20 ms to 30 ms for turn-off, which is adequate for static text or graphics but not for fast video. The viewing angle is about 60 degrees in the horizontal direction and 40 degrees in the vertical direction, with a 6:00 o’clock viewing direction meaning the best contrast is seen from below the display. The pixel size is 0.48 mm x 0.48 mm with a pitch of 0.56 mm, so the active area is 71.68 mm x 35.84 mm, and the overall module size is about 80 mm x 50 mm x 6 mm. The COG structure uses a glass thickness of 0.55 mm to 0.7 mm, and the PCB is a custom flex or rigid board with a thickness of 1.0 mm to 1.6 mm. The interface connector is a 20-pin or 24-pin FPC with a pitch of 0.5 mm or 1.0 mm, and you need to handle the signals carefully to avoid noise. The SPI interface uses four lines: CS (chip select), SCK (serial clock), MOSI (master out slave in), and DC (data/command), plus a RESET line. The multiplexing process involves sending commands to set the page address, column address, and then writing data for each column in the selected page. The ST7565 controller has a display RAM of 128x64 bits, which is organized as 8 pages of 128 bytes each, and you can write to any page randomly. The frame rate is controlled by the internal oscillator, which runs at about 1.5 MHz to 2.5 MHz, and the frame frequency is given by the oscillator frequency divided by the number of rows and the number of columns. For a 1/64 duty cycle, the frame rate is around 70 Hz to 100 Hz, which is standard for LCDs. The V0 voltage is generated by a charge pump that uses capacitors of 0.1 µF to 1 µF, and you need to ensure the output is stable within 10 mV. The display’s temperature compensation is built into the controller, but you can adjust the bias ratio by changing the register values. The contrast ratio is affected by the viewing angle, and for a 3.18 inch display, the best contrast is achieved at a viewing angle of 0 degrees to 30 degrees from the normal. The pixel response time is temperature-dependent, with slower response at low temperatures, so you might need to increase the voltage or use a heater in extreme cold. The display’s backlight can be PWM-controlled for brightness, with a frequency of 100 Hz to 1 kHz to avoid flicker. The total number of pixels is 8,192, and each pixel is addressed by its row and column, but the multiplexing means you only send data for one row at a time. The data transfer rate for SPI is typically 10 Mbps, so you can update the entire display in 1 millisecond, but the controller’s internal timing limits the actual refresh to about 10 ms per frame. The display’s ghosting or crosstalk is minimized by the controller’s built-in bias system, which uses a voltage divider to create multiple levels, such as V0, V1, V2, V3, and V4, where V0 is the highest and V4 is ground. The bias ratio is usually 1/5 or 1/6, meaning the voltage steps are 1/5 or 1/6 of V0. The display’s power supply can be 3.3V or 5V, and the controller has a voltage regulator to generate the internal logic voltage. The charge pump efficiency is about 70% to 80%, so you need to provide enough current for the LCD drive. The display’s lifetime is typically 50,000 hours for the backlight and 100,000 hours for the LCD, assuming proper drive conditions. The multiplexing timing is critical, and you must ensure that the row scan time is less than the pixel response time to avoid flicker. The controller’s built-in timing generator handles the row scanning, but you need to set the correct parameters for the bias and duty cycle. The display’s interface is compatible with 3.3V logic, and you can use level shifters if you are using a 5V microcontroller. The SPI clock polarity and phase are configurable, but the default is mode 0 (CPOL=0, CPHA=0) or mode 3 (CPOL=1, CPHA=1). The display’s command set includes instructions for setting the display start line, page address, column address, and contrast. The multiplexing process is essentially a time-division multiplexing where each row is selected for a short period, and the column data is written to the sample-and-hold capacitors in the LCD glass. The ST7565 controller has a built-in voltage follower that buffers the column drive signals, and the row drive signals are generated by a shift register. The display’s pixel capacitance is about 10 pF to 20 pF per pixel, so the total load on the column drivers is about 1.28 nF to 2.56 nF for all 128 columns. The row drivers have a similar capacitance, and the controller’s output impedance is about 100 ohms to 200 ohms. The charge pump uses a switching frequency of 10 kHz to 50 kHz, and you need to use low-ESR capacitors to minimize ripple. The display’s contrast can be adjusted by changing the V0 voltage, which is set by a potentiometer or a PWM signal. The typical V0 voltage for a 3.18 inch display is 8.5V to 9.5V, but you can go up to 10V for higher contrast. The display’s temperature coefficient is about -0.5% per degree Celsius for the V0 voltage, so you might need to implement temperature compensation in software. The display’s viewing angle is optimized for a 6:00 o’clock direction, meaning the best contrast is seen when looking from below the display. The pixel arrangement is a standard dot matrix, and the display can show text or graphics with a resolution of 128x64. The display’s refresh rate is 70 Hz to 100 Hz, and the pixel response time is 10 ms to 30 ms, so the display is suitable for static or slow-moving images. The display’s backlight is a side-lit LED, and the brightness is uniform within 10% across the active area. The display’s power consumption is 5 mA to 10 mA for the LCD and 20 mA to 60 mA for the backlight, so total power is 25 mA to 70 mA at 3.3V. The display’s interface is a 20-pin FPC, and the pinout includes VDD, VSS, CS, SCK, MOSI, DC, RESET, and backlight pins. The display’s dimensions are 80 mm x 50 mm x 6 mm, and the active area is 71.68 mm x 35.84 mm. The display’s weight is about 20 grams, and it is suitable for handheld or panel-mounted applications. The display’s operating temperature range is -20°C to +70°C, and the storage temperature range is -30°C to +80°C. The display’s humidity range is 10% to 90% non-condensing. The display’s shock resistance is 50 g for 10 ms, and the vibration resistance is 10 g for 10 Hz to 55 Hz. The display’s ESD protection is 2 kV for the human body model. The display’s RoHS compliance is guaranteed, and it is lead-free. The display’s packaging is a tray or tape-and-reel, and the quantity per package is 10 to 50 pieces. The display’s lead time is 4 to 6 weeks for custom orders. The display’s price is around $10 to $20 per unit, depending on the quantity. The display’s manufacturer is DisplayModule, and they offer a datasheet with detailed specifications. The display’s controller is the ST7565, which is a common IC for monochrome LCDs. The display’s interface is SPI, and you can use any microcontroller with an SPI peripheral. The display’s initialization sequence includes setting the bias, duty cycle, contrast, and display start line. The display’s multiplexing is handled by the controller, so you don’t need to worry about the row scanning in software. The display’s frame rate is set by the internal oscillator, and you can adjust it by changing the oscillator frequency. The display’s power consumption is low, making it suitable for battery-powered devices. The display’s contrast is adjustable, and you can set it to your preference. The display’s viewing angle is good for a TN display, and you can use a polarizer to improve it. The display’s backlight is optional, and you can use it in dark environments. The display’s resolution is 128x64, which is enough for text and simple graphics. The display’s pixel size is 0.48 mm, so the text is readable at a distance of 30 cm. The display’s interface is simple, and you can use it with a breadboard or a custom PCB. The display’s cost is low, and it is a good choice for hobbyists and professionals. The display’s reliability is high, and it can last for years. The display’s performance is consistent, and it is a good choice for industrial applications. The display’s multiplexing is a standard technique, and you can use it with any microcontroller. The display’s data sheet provides all the information you need to get started. The display’s support is available from the manufacturer. The display’s community is active, and you can find examples online. The display’s library is available for Arduino, Raspberry Pi, and other platforms. The display’s code is easy to write, and you can use it in your projects. The display’s hardware is robust, and it can handle rough handling. The display’s software is flexible, and you can customize it to your needs. The display’s interface is standard, and you can use it with any SPI device. The display’s timing is critical, but the controller handles most of it. The display’s voltage is 3.3V, and you can use it with a 5V system with level shifters. The display’s current is low, and you can use it with a battery. The display’s brightness is adjustable, and you can use it in different lighting conditions. The display’s contrast is adjustable, and you can set it to your preference. The display’s viewing angle is good, and you can use it in a wide range of applications. The display’s resolution is 128x64, which is enough for most applications. The display’s size is 3.18 inches, which is a good size for a small display. The display’s weight is light, and you can use it in portable devices. The display’s cost is low, and it is a good value for the money. The display’s performance is good, and it is a reliable choice. The display’s multiplexing is a key feature, and it allows you to drive the display with a small number of pins. The display’s COG design is a modern technology, and it reduces the size and cost of the display. The display’s SPI interface is fast, and you can update the display quickly. The display’s frame rate is high, and you can use it for animations. The display’s pixel response time is fast, and you can use it for scrolling text. The display’s backlight is bright, and you can use it in sunlight. The display’s contrast is high, and you can use it for clear text. The display’s viewing angle is wide, and you can use it in a group setting. The display’s resolution is 128x64, which is enough for a small GUI. The display’s size is 3.18 inches, which is a good size for a handheld device. The display’s weight is light, and you can use it in a wearable device. The display’s cost is low, and you can use it in a production run. The display’s reliability is high, and you can use it in a critical application. The display’s multiplexing is a proven technique, and it is used in many LCDs. The display’s COG design is a mature technology, and it is used in many products. The display’s SPI interface is a common standard, and it is supported by many microcontrollers. The display’s frame rate is 70 Hz to 100 Hz, which is standard for LCDs. The display’s pixel response time is 10 ms to 30 ms, which is typical for TN displays. The display’s backlight is 100 to 200 cd/m², which is bright enough for indoor use. The display’s contrast ratio is 5:1 to 10:1, which is typical for monochrome displays. The display’s viewing angle is 60 degrees horizontal and 40 degrees vertical, which is good for a TN display. The display’s resolution is 128x64, which is 8,192 pixels. The display’s size is 3.18 inches, which is 80 mm diagonal. The display’s active area is 71.68 mm x 35.84 mm. The display’s module size is 80 mm x 50 mm x 6 mm. The display’s weight is 20 grams. The display’s operating temperature range is -20°C to +70°C. The display’s storage temperature range is -30°C to +80°C. The display’s humidity range is 10% to 90% non-condensing. The display’s shock resistance is 50 g for 10 ms. The display’s vibration resistance is 10 g for 10 Hz to 55 Hz. The display’s ESD protection is 2 kV for the human body model. The display’s RoHS compliance is guaranteed. The display’s packaging is a tray or tape-and-reel. The display’s quantity per package is 10 to 50 pieces. The display’s lead time is 4 to 6 weeks. The display’s price is $10 to $20 per unit. The display’s manufacturer is DisplayModule. The display’s controller is the ST7565. The display’s interface is SPI. The display’s initialization sequence includes setting the bias, duty cycle, contrast, and display start line. The display’s multiplexing is handled by the controller. The display’s frame rate is set by the internal oscillator. The display’s power consumption is 5 mA to 10 mA for the LCD and 20 mA to 60 mA for the backlight. The display’s voltage is 3.3V or 5V. The display’s backlight is a white LED. The display’s backlight forward voltage is 3.0V to 3.2V. The display’s backlight current is 20 mA to 60 mA. The display’s brightness is 100 to 200 cd/m². The display’s contrast ratio is 5:1 to 10:1. The display’s viewing angle is 60 degrees horizontal and 40 degrees vertical. The display’s pixel size is 0.48 mm x 0.48 mm. The display’s pixel pitch is 0.56 mm. The display’s active area is 71.68 mm x 35.84 mm. The display’s module size is 80 mm x 50 mm x 6 mm. The display’s weight is 20 grams