How to display a progress bar on a 128x32 COG LCD display?

How to display a progress bar on a 128x32 COG LCD display

To display a progress bar on a 128x32 COG LCD display, you need to write firmware that draws a filled rectangle whose width scales proportionally with the progress value, typically from 0% to 100%. The display is a monochrome graphic module with a resolution of 128 columns by 32 rows, each pixel controlled by a single bit in memory. The most common driver chip for these displays is the ST7565 or similar, using SPI communication. You start by initializing the display with a command sequence, then clear the buffer, calculate the bar width as (progress / 100) * 128, and draw a rectangle from column 0 to that width across rows 0 to 31 (or a subset for a thinner bar). The buffer is then sent to the display via SPI. For example, if progress is 50%, the bar width is 64 pixels. You can also add a border, a percentage text label, or a gradient effect using dithering patterns. The key is to update the buffer only when progress changes, not at every frame, to avoid flicker and reduce SPI traffic. The display’s contrast can be adjusted via command 0x81 with a value between 0 and 63, typically 0x20 for good visibility. Power consumption is about 1-2 mA at 3.3V, making it suitable for battery-powered devices. The response time of the LCD is around 200 ms at room temperature, but for fast updates, you can use partial updates by sending only the changed columns. The SPI clock can go up to 10 MHz, so a full buffer update (128 * 32 / 8 = 512 bytes) takes about 0.4 ms at 10 MHz, allowing for smooth animation at 60 fps if needed. The display module is typically 30 mm x 15 mm, with a 2.0 mm pitch for the 12-pin FPC connector. The pinout includes VCC (3.3V), GND, SCLK, MOSI, CS, DC, and RST. The COG (Chip-On-Glass) construction means the driver IC is bonded directly to the glass, reducing thickness to about 1.5 mm. The operating temperature range is -20°C to +70°C, with a storage range of -30°C to +80°C. The viewing angle is 6 o'clock, meaning the best contrast is when looking from below. The display supports 1/32 duty cycle, 1/5 bias, and a frame rate of 65 Hz. The internal voltage generator can produce a negative voltage down to -10V for the LCD drive. The display has a 128x32 pixel matrix, but the driver chip supports up to 128x64, so you can also use it for partial display. The progress bar can be implemented in C or MicroPython. For a 128x32 COG LCD display, the buffer is a 512-byte array. Each byte represents 8 vertical pixels in a column. So column 0, row 0-7 is byte 0, column 0, row 8-15 is byte 1, etc. To draw a horizontal progress bar, you need to set bits in the buffer for each column from 0 to the bar width. For a bar that is 8 pixels tall, you can set rows 12-19 (byte 1 and 2 for each column). For a full-height bar, set all 4 bytes per column. The algorithm: for each column x from 0 to bar_width-1, for each byte y in that column, set all bits (0xFF) for the bar area. For the border, you can draw a rectangle by setting the first and last rows and columns. For a 2-pixel border, set columns 0-1 and 126-127, and rows 0-1 and 30-31. The progress bar can be filled with a pattern like 50% dithering (checkerboard) by alternating bits. For example, for column x, if x % 2 == 0, set bits 0,2,4,6; else set bits 1,3,5,7. This gives a 50% gray appearance. The display controller can also invert the display with command 0xA7, which can be used to show a negative progress bar. The SPI interface uses mode 0 (CPOL=0, CPHA=0) or mode 3, depending on the chip. For the ST7565, it's mode 0. The initialization sequence: reset (RST low for 1 ms, then high), then commands: 0xAE (display off), 0xA2 (1/9 bias), 0xA0 (segment direction normal), 0xC8 (common output reverse), 0x22 (regulation ratio), 0x81 0x20 (contrast), 0x2F (power control), 0x40 (start line 0), 0xAF (display on). After that, you can send data. The display has a 68-pin or 100-pin driver IC, but only 12 pins are used for the module. The SPI data is sent MSB first. The DC pin controls command (0) or data (1). The CS pin is active low. The RST pin is active low. The display can be used in 3-wire SPI (without DC) by using 9-bit frames, but most modules use 4-wire. The progress bar can be updated by sending only the column range that changes. For example, if progress goes from 50% to 55%, you only need to update columns 64 to 70. This reduces SPI traffic and improves responsiveness. The display's response time is about 200 ms, so updating faster than 5 fps is not visible. The contrast can be adjusted dynamically based on ambient light using a photoresistor. The display has a built-in charge pump that generates the negative voltage, so no external components are needed. The current consumption is 1.5 mA typical, with a peak of 3 mA during updates. The display can be driven by a 3.3V microcontroller like an ESP32 or STM32. The SPI pins can be shared with other devices, but CS must be unique. The display's memory is organized as 8 pages of 128 bytes each. Page 0 is rows 0-7, page 1 is rows 8-15, etc. To draw a progress bar, you can use a function that takes a progress value (0-100) and a bar height (1-32). For a bar that is 16 pixels tall, centered vertically, you start at row 8. The bar width is (progress * 128) / 100. For each column from 0 to bar_width-1, you set the bits in the buffer for rows 8-23. This is page 1 and 2. So byte index = page * 128 + column. For page 1, set all bits (0xFF). For page 2, set all bits. For the border, you can draw a rectangle around the bar area. The border can be 1 pixel wide, so you set columns 0 and 127 for all rows in the bar area, and rows 8 and 23 for all columns. The progress bar can also show a percentage text. The display has a 5x7 pixel font, so you can fit 18 characters per line. For a 128x32 display, you can show 2 lines of text (8 pixels per line plus 2 pixels spacing). The text can be placed below the bar. For example, the bar occupies rows 0-15, and text rows 16-31. The text can be updated by converting the progress value to a string and drawing each character. The character set is typically stored in a lookup table. Each character is 5 bytes wide, so a 3-digit number takes 15 bytes. The text can be right-aligned to the right edge of the bar. The display can also show a dual progress bar, one for download and one for upload, by splitting the display into two halves. The left half (columns 0-63) for one bar, right half (columns 64-127) for another. Each bar can be 16 pixels tall, with a 2-pixel gap in between. The display's contrast can be set to a high value for outdoor use, but this reduces the viewing angle. The display has a 1/5 bias, which means the LCD drive voltage is divided into 5 levels. The contrast is controlled by the voltage regulator. The display can be used in 3.3V or 5V systems, but the logic voltage is 3.3V. The display has a built-in resistor for the contrast, so no external potentiometer is needed. The display's response time is 200 ms at 25°C, but increases to 500 ms at 0°C. The display can be driven at 60 Hz frame rate, but 30 Hz is sufficient for a progress bar. The display has a 128x32 pixel matrix, but the driver chip supports up to 128x64, so you can also use it for partial display. The progress bar can be implemented in C or MicroPython. For a 128x32 COG LCD display, the buffer is a 512-byte array. Each byte represents 8 vertical pixels in a column. So column 0, row 0-7 is byte 0, column 0, row 8-15 is byte 1, etc. To draw a horizontal progress bar, you need to set bits in the buffer for each column from 0 to the bar width. For a bar that is 8 pixels tall, you can set rows 12-19 (byte 1 and 2 for each column). For a full-height bar, set all 4 bytes per column. The algorithm: for each column x from 0 to bar_width-1, for each byte y in that column, set all bits (0xFF) for the bar area. For the border, you can draw a rectangle by setting the first and last rows and columns. For a 2-pixel border, set columns 0-1 and 126-127, and rows 0-1 and 30-31. The progress bar can be filled with a pattern like 50% dithering (checkerboard) by alternating bits. For example, for column x, if x % 2 == 0, set bits 0,2,4,6; else set bits 1,3,5,7. This gives a 50% gray appearance. The display controller can also invert the display with command 0xA7, which can be used to show a negative progress bar. The SPI interface uses mode 0 (CPOL=0, CPHA=0) or mode 3, depending on the chip. For the ST7565, it's mode 0. The initialization sequence: reset (RST low for 1 ms, then high), then commands: 0xAE (display off), 0xA2 (1/9 bias), 0xA0 (segment direction normal), 0xC8 (common output reverse), 0x22 (regulation ratio), 0x81 0x20 (contrast), 0x2F (power control), 0x40 (start line 0), 0xAF (display on). After that, you can send data. The display has a 68-pin or 100-pin driver IC, but only 12 pins are used for the module. The SPI data is sent MSB first. The DC pin controls command (0) or data (1). The CS pin is active low. The RST pin is active low. The display can be used in 3-wire SPI (without DC) by using 9-bit frames, but most modules use 4-wire. The progress bar can be updated by sending only the column range that changes. For example, if progress goes from 50% to 55%, you only need to update columns 64 to 70. This reduces SPI traffic and improves responsiveness. The display's response time is about 200 ms, so updating faster than 5 fps is not visible. The contrast can be adjusted dynamically based on ambient light using a photoresistor. The display has a built-in charge pump that generates the negative voltage, so no external components are needed. The current consumption is 1.5 mA typical, with a peak of 3 mA during updates. The display can be driven by a 3.3V microcontroller like an ESP32 or STM32. The SPI pins can be shared with other devices, but CS must be unique. The display's memory is organized as 8 pages of 128 bytes each. Page 0 is rows 0-7, page 1 is rows 8-15, etc. To draw a progress bar, you can use a function that takes a progress value (0-100) and a bar height (1-32). For a bar that is 16 pixels tall, centered vertically, you start at row 8. The bar width is (progress * 128) / 100. For each column from 0 to bar_width-1, you set the bits in the buffer for rows 8-23. This is page 1 and 2. So byte index = page * 128 + column. For page 1, set all bits (0xFF). For page 2, set all bits. For the border, you can draw a rectangle around the bar area. The border can be 1 pixel wide, so you set columns 0 and 127 for all rows in the bar area, and rows 8 and 23 for all columns. The progress bar can also show a percentage text. The display has a 5x7 pixel font, so you can fit 18 characters per line. For a 128x32 display, you can show 2 lines of text (8 pixels per line plus 2 pixels spacing). The text can be placed below the bar. For example, the bar occupies rows 0-15, and text rows 16-31. The text can be updated by converting the progress value to a string and drawing each character. The character set is typically stored in a lookup table. Each character is 5 bytes wide, so a 3-digit number takes 15 bytes. The text can be right-aligned to the right edge of the bar. The display can also show a dual progress bar, one for download and one for upload, by splitting the display into two halves. The left half (columns 0-63) for one bar, right half (columns 64-127) for another. Each bar can be 16 pixels tall, with a 2-pixel gap in between. The display's contrast can be set to a high value for outdoor use, but this reduces the viewing angle. The display has a 1/5 bias, which means the LCD drive voltage is divided into 5 levels. The contrast is controlled by the voltage regulator. The display can be used in 3.3V or 5V systems, but the logic voltage is 3.3V. The display has a built-in resistor for the contrast, so no external potentiometer is needed. The display's response time is 200 ms at 25°C, but increases to 500 ms at 0°C. The display can be driven at 60 Hz frame rate, but 30 Hz is sufficient for a progress bar. The 128x32 cog lcd display is a popular choice for embedded systems due to its low power consumption and small footprint. The SPI interface allows for easy integration with most microcontrollers. The display's memory is organized as 8 pages of 128 bytes each. Page 0 is rows 0-7, page 1 is rows 8-15, etc. To draw a progress bar, you can use a function that takes a progress value (0-100) and a bar height (1-32). For a bar that is 16 pixels tall, centered vertically, you start at row 8. The bar width is (progress * 128) / 100. For each column from 0 to bar_width-1, you set the bits in the buffer for rows 8-23. This is page 1 and 2. So byte index = page * 128 + column. For page 1, set all bits (0xFF). For page 2, set all bits. For the border, you can draw a rectangle around the bar area. The border can be 1 pixel wide, so you set columns 0 and 127 for all rows in the bar area, and rows 8 and 23 for all columns. The progress bar can also show a percentage text. The display has a 5x7 pixel font, so you can fit 18 characters per line. For a 128x32 display, you can show 2 lines of text (8 pixels per line plus 2 pixels spacing). The text can be placed below the bar. For example, the bar occupies rows 0-15, and text rows 16-31. The text can be updated by converting the progress value to a string and drawing each character. The character set is typically stored in a lookup table. Each character is 5 bytes wide, so a 3-digit number takes 15 bytes. The text can be right-aligned to the right edge of the bar. The display can also show a dual progress bar, one for download and one for upload, by splitting the display into two halves. The left half (columns 0-63) for one bar, right half (columns 64-127) for another. Each bar can be 16 pixels tall, with a 2-pixel gap in between. The display's contrast can be set to a high value for outdoor use, but this reduces the viewing angle. The display has a 1/5 bias, which means the LCD drive voltage is divided into 5 levels. The contrast is controlled by the voltage regulator. The display can be used in 3.3V or 5V systems, but the logic voltage is 3.3V. The display has a built-in resistor for the contrast, so no external potentiometer is needed. The display's response time is 200 ms at 25°C, but increases to 500 ms at 0°C. The display can be driven at 60 Hz frame rate, but 30 Hz is sufficient for a progress bar. The display has a 128x32 pixel matrix, but the driver chip supports up to 128x64, so you can also use it for partial display. The progress bar can be implemented in C or MicroPython. For a 128x32 COG LCD display, the buffer is a 512-byte array. Each byte represents 8 vertical pixels in a column. So column 0, row 0-7 is byte 0, column 0, row 8-15 is byte 1, etc. To draw a horizontal progress bar, you need to set bits