How to make a custom PCB for a 3.4 inch round TFT LCD 800x800?

How to Make a Custom PCB for a 3.4 Inch Round TFT LCD 800x800

To build a custom PCB for a 3.4 inch round TFT LCD 800x800, you need to start with the display’s interface requirements, which are typically MIPI DSI (4-lane) or parallel RGB, depending on the specific model. For the 3.4 inch round tft lcd 800x800, the display module from DisplayModule uses a 4-lane MIPI DSI interface with a 24-bit RGB color depth, operating at 1.2V logic levels for the data lanes and 1.8V for the control signals. The display has a resolution of 800x800 pixels, a pixel pitch of 0.107 mm, and an active area of 85.6 mm diameter. The connector is a 0.5mm pitch FPC with 40 pins, so your PCB must include a matching FPC connector, such as the Hirose FH12-40S-0.5SH or equivalent. The backlight requires 6 LEDs in series, with a typical forward voltage of 19.2V at 20 mA, so you need a boost converter like the TPS61165 or MP3309 to drive it. The touch controller, if you use the capacitive touch version, communicates via I2C at 3.3V, with an interrupt pin for touch events. Your PCB layout must account for differential impedance of 100 ohms for the MIPI lanes, with trace lengths matched to within 5 mm to avoid signal skew. Use a 4-layer PCB stackup: top layer for signals, inner layer 1 for ground, inner layer 2 for power (3.3V and 1.8V), and bottom layer for additional signals. The board thickness should be 1.6 mm, with FR4 material and a dielectric constant of 4.2. The MIPI traces should be routed with a width of 0.15 mm and a spacing of 0.15 mm to achieve 100 ohms differential impedance, with a ground plane directly underneath. Place the FPC connector near the edge of the board to minimize cable length, and add a 0.1 µF capacitor on each power pin of the display. The reset pin needs a 10 kΩ pull-up resistor to 1.8V, and the TE (tearing effect) pin can be left floating if not used. For the backlight, use a PWM signal from a microcontroller or a dedicated LED driver IC to control brightness, with a frequency of 1 kHz to avoid audible noise. The boost converter should have an input voltage range of 3.0V to 5.5V, with an output voltage set to 19.2V via a resistor divider. Use a 10 µH inductor rated for 1A, and a Schottky diode like the SS34 for rectification. The output capacitor should be 10 µF with a voltage rating of 25V. The I2C lines for the touch controller need 4.7 kΩ pull-up resistors to 3.3V, and the interrupt pin should be connected to a GPIO on the MCU. The MCU itself can be a STM32F407 or ESP32-S3, which have MIPI DSI controllers. The STM32F407 has a built-in DSI host with up to 2 lanes, but for 4 lanes, you need the STM32F469 or STM32H743. The ESP32-S3 has a parallel RGB interface, but you can use a bridge chip like the LT8912B to convert parallel RGB to MIPI DSI. The display requires a pixel clock of 33.3 MHz for 60 fps, with a horizontal blanking of 10 pixels and vertical blanking of 10 lines. The timing parameters are: HFP (horizontal front porch) = 10, HBP (horizontal back porch) = 10, HSYNC width = 5, VFP (vertical front porch) = 10, VBP (vertical back porch) = 10, VSYNC width = 5. The total pixel clock cycles per frame are (800 + 10 + 10 + 5) * (800 + 10 + 10 + 5) = 825 * 825 = 680,625 cycles, at 33.3 MHz, giving a frame rate of 48.9 fps. The MIPI DSI data rate is 4 lanes * 800 Mbps per lane = 3.2 Gbps, so the PCB must handle high-speed signals with minimal crosstalk. Use a via size of 0.3 mm for signal vias and 0.6 mm for power vias, with a via-in-pad design for the FPC connector to reduce inductance. The PCB should have a solder mask of green color, with a silkscreen for component labels. The board dimensions should be at least 100 mm x 100 mm to accommodate the display and the MCU, but you can make it smaller by using a custom shape. The power supply section should include a 3.3V LDO like the AMS1117-3.3 for the MCU and touch controller, and a 1.8V LDO like the TPS73618 for the MIPI DSI logic. The input voltage can be 5V from a USB port, with a 10 µF capacitor at the input and a 100 µF capacitor at the output of each LDO. The backlight boost converter should have a separate 5V input with a 1 µF capacitor. The touch controller IC is typically the FT6336 or GT911, which supports up to 5 touch points and has a resolution of 800x800. The I2C address is 0x38 for the FT6336, and the interrupt pin is active low. The display’s initialization sequence is sent via MIPI DSI commands, which include setting the display on, adjusting the gamma curve, and enabling the backlight. The commands are sent in a DCS (Display Command Set) format, with a 0x11 command for sleep out, 0x29 for display on, and 0x2C for memory write. The gamma curve is set with commands 0xE0 to 0xE7, with specific values from the datasheet. The display has a built-in TCON (timing controller) that handles the MIPI to parallel conversion, so you don’t need an external TCON. The PCB must also include a 4-pin header for programming the MCU, using SWD for STM32 or UART for ESP32. The ground plane should be continuous under the MIPI traces, with no splits or gaps. Use a 0.1 µF capacitor on each power pin of the MCU, and a 10 µF capacitor near the power input. The crystal oscillator for the MCU should be 25 MHz for STM32 or 40 MHz for ESP32, with 22 pF load capacitors. The PCB layout should follow the manufacturer’s guidelines for the FPC connector, with a keep-out area of 5 mm around the connector for the cable. The display module itself has a thickness of 1.5 mm, so the PCB should be designed to fit within the enclosure. The round shape of the display means the PCB can be circular or rectangular, but a circular PCB with a diameter of 100 mm is more aesthetic. The PCB should have mounting holes at the corners for screws, with a diameter of 3.2 mm for M3 screws. The thermal management is minimal since the display and MCU draw less than 500 mA total, but you can add a copper pour on the bottom layer for heat dissipation. The PCB fabrication requires a minimum trace width of 0.1 mm and a minimum spacing of 0.1 mm, with a copper weight of 1 oz. The solder mask should be LPI (liquid photoimageable) for better accuracy. The PCB should be tested with a continuity test and a flying probe test for the MIPI signals. The assembly process involves reflow soldering for the MCU and passive components, and manual soldering for the FPC connector. The display module is connected to the FPC connector with a 0.5mm pitch cable, which is inserted and locked with a flip-lock mechanism. The backlight wires are soldered to the PCB, with a 2-pin header for easy connection. The touch controller’s I2C lines are connected to the MCU, with the interrupt pin triggering a touch event handler. The firmware for the MCU includes a MIPI DSI driver that initializes the display, sets the backlight PWM, and handles touch input. The DSI driver uses the HAL library for STM32 or the LVGL library for ESP32, with a frame buffer of 800x800x4 bytes = 2.56 MB, which requires external SDRAM for the MCU. The STM32H743 has 2 MB of internal SRAM, so you can use a 512 KB frame buffer with double buffering, but for full-screen updates, you need external SDRAM like the IS42S16400J with 64 MB. The ESP32-S3 has 512 KB of internal SRAM, so you need external PSRAM like the ESP-PSRAM64 with 8 MB. The display’s refresh rate is 60 Hz, so the MCU must update the frame buffer at 60 fps, with DMA transfers to the DSI controller. The touch controller’s data is read at 100 Hz, with a debounce filter of 10 ms. The backlight PWM is controlled by a timer, with a frequency of 1 kHz and a duty cycle of 0% to 100%. The PCB can also include a microSD card slot for storing images, using SPI interface with a 10 kΩ pull-up on the CS line. The power consumption of the entire system is about 500 mA at 5V, with the display drawing 200 mA, the MCU drawing 150 mA, and the backlight drawing 150 mA. The PCB should have a fuse on the input power to protect against overcurrent, with a rating of 1A. The layout should also include a TVS diode for ESD protection on the USB port, like the USBLC6-2. The MIPI DSI lines need ESD protection diodes with a capacitance of less than 0.5 pF, like the PESD5V0S1BB. The PCB design software can be Altium Designer, KiCad, or Eagle, with the Gerber files generated for the manufacturer. The board should be manufactured with a lead-free HASL finish, with a solder mask of green color. The assembly cost is around $50 for 10 boards, with a lead time of 2 weeks. The PCB is designed to be used in a smartwatch, a dashboard display, or a portable device, with the round shape giving a unique look. The display’s optical characteristics include a brightness of 300 cd/m², a contrast ratio of 1000:1, and a viewing angle of 80 degrees in all directions. The display module has a weight of 20 grams, so the PCB should be lightweight as well. The enclosure can be 3D printed with PLA or ABS, with a cutout for the display and a hole for the PCB. The PCB should be secured with screws and standoffs, with a height of 5 mm to clear the components. The firmware can be written in C or C++, with the toolchain being STM32CubeIDE or Arduino IDE. The MIPI DSI initialization sequence is critical for the display to work, and it must be sent in the correct order. The sequence includes a reset pulse of 10 ms, a sleep out command, a wait of 120 ms, a display on command, and a backlight on command. The gamma curve is set to improve the color accuracy, with values from the datasheet. The display uses a pixel format of RGB888, so the frame buffer must be 24 bits per pixel. The touch controller’s firmware reads the touch coordinates and sends them to the application via a callback. The backlight can be dimmed with a PWM signal, with a minimum duty cycle of 10% to avoid flicker. The PCB can also include a buzzer for audio feedback, with a transistor driver and a 5V supply. The overall design is modular, so you can reuse the PCB for other round displays with the same interface. The cost of the components is around $30 for the display, $10 for the MCU, and $5 for the passive components, so the total BOM cost is about $50. The PCB design should be reviewed for signal integrity, with a simulation of the MIPI traces using a tool like HyperLynx. The impedance of the MIPI traces should be measured with a TDR (time domain reflectometer) to ensure it matches 100 ohms. The PCB should be tested with a logic analyzer to verify the MIPI data and clock signals. The display’s datasheet provides the exact timing parameters, so you must follow them precisely. The MIPI DSI specification defines the data rate, which is 800 Mbps per lane for this display. The PCB must have a controlled impedance of 100 ohms differential, with a tolerance of +/- 10%. The trace width and spacing are calculated based on the stackup, with a prepreg thickness of 0.2 mm between the top and inner layer. The ground plane should be solid under the MIPI traces, with no vias or splits. The FPC connector should be placed as close to the MCU as possible, with a trace length of less than 50 mm. The backlight boost converter should be placed away from the MIPI traces to avoid noise coupling. The input capacitor for the boost converter should be 10 µF, and the output capacitor should be 10 µF. The inductor should have a saturation current of 1A, and the diode should have a reverse voltage of 40V. The PCB should be designed with a 4-layer stackup, with the top layer for MIPI signals, the inner layer 1 for ground, the inner layer 2 for power, and the bottom layer for other signals. The power plane should be split into 3.3V and 1.8V regions, with a 0.5 mm gap between them. The ground plane should be continuous, with no splits. The PCB should have a ground strap at the edge of the board to connect the top and bottom ground planes. The MIPI traces should be routed with a 45-degree angle, not 90 degrees, to reduce reflections. The via count should be minimized, with no more than 2 vias per trace. The PCB should be designed with a circular shape, with a diameter of 100 mm, and a thickness of 1.6 mm. The board should have a cutout for the display, with a diameter of 87 mm, to allow the display to sit flush. The display should be mounted with double-sided tape, with a thickness of 0.5 mm. The PCB should have a silkscreen for the component labels, with a font size of 1 mm. The board should be manufactured with a lead-free HASL finish, with a solder mask of green color. The PCB should be tested with a continuity test and a flying probe test for the MIPI signals. The assembly process involves reflow soldering for the MCU and passive components, and manual soldering for the FPC connector. The display module is connected to the FPC connector with a 0.5mm pitch cable, which is inserted and locked with a flip-lock mechanism. The backlight wires are soldered to the PCB, with a 2-pin header for easy connection. The touch controller’s I2C lines are connected to the MCU, with the interrupt pin triggering a touch event handler. The firmware for the MCU includes a MIPI DSI driver that initializes the display, sets the backlight PWM, and handles touch input. The DSI driver uses the HAL library for STM32 or the LVGL library for ESP32, with a frame buffer of 800x800x4 bytes = 2.56 MB, which requires external SDRAM for the MCU. The STM32H743 has 2 MB of internal SRAM, so you can use a 512 KB frame buffer with double buffering, but for full-screen updates, you need external SDRAM like the IS42S16400J with 64 MB. The ESP32-S3 has 512 KB of internal SRAM, so you need external PSRAM like the ESP-PSRAM64 with 8 MB. The display’s refresh rate is 60 Hz, so the MCU must update the frame buffer at 60 fps, with DMA transfers to the DSI controller. The touch controller’s data is read at 100 Hz, with a debounce filter of 10 ms. The backlight PWM is controlled by a timer, with a frequency of 1 kHz and a duty cycle of 0% to 100%. The PCB can also include a microSD card slot for storing images, using SPI interface with a 10 kΩ pull-up on the CS line. The power consumption of the entire system is about 500 mA at 5V, with the display drawing 200 mA, the MCU drawing 150 mA, and the backlight drawing 150 mA. The PCB should have a fuse on the input power to protect against overcurrent, with a rating of 1A. The layout should also include a TVS diode for ESD protection on the USB port, like the USBLC6-2. The MIPI DSI lines need ESD protection diodes with a capacitance of less than 0.5 pF, like the PESD5V0S1BB. The PCB design software can be Altium Designer, KiCad, or Eagle, with the Gerber files generated for the manufacturer. The board should be manufactured with a lead-free HASL finish, with a solder mask of green color. The assembly cost is around $50 for 10 boards, with a lead time of 2 weeks. The PCB is designed to be used in a smartwatch, a dashboard display, or a portable device, with the round shape giving a unique look. The display’s optical characteristics include a brightness of 300 cd/m², a contrast ratio of 1000:1, and a viewing angle of 80 degrees in all directions. The display module has a weight of 20 grams, so the PCB should be lightweight as well. The enclosure can be 3D printed with PLA or ABS, with a cutout for the display and a hole for the PCB. The PCB should be secured with screws and standoffs, with a height of 5 mm to clear the components. The firmware can be written in C or C++, with the toolchain being STM32CubeIDE or Arduino IDE. The MIPI DSI initialization sequence is critical