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9904 – 3.5inch RPi LCD (A)/en

Aus JW Tech Wiki

Documentation notice: This technical documentation was independently rewritten from an archived supplier source. Check technical details and commands against the product version and manufacturer documentation before use.

Summary

The 3.5inch RPi LCD (A) is a 3.5-inch resistive touch display with a 480 × 320 resolution and an SPI interface connected via the Raspberry Pi's GPIO header. It is physically sized to plug directly onto a Raspberry Pi 3/4/5.

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Technical overview

  • Resolution: 480 × 320 pixels
  • Interface: SPI via the display's 26-pin connector; the Raspberry Pi provides 40 GPIO pins
  • Connection: The display connector plugs into the GPIO header; pin mapping must be observed
  • Pin 11 (TP_IRQ): Touch panel interrupt, low level when touched
  • Pins 19 and 23 are shared between LCD and touch panel (LCD_SI/TP_SI and LCD_SCK/TP_SCK)
  • Pins 24 and 26 are chip-select signals for the LCD and touch panel respectively
  • Compatibility: Works with all Raspberry Pi versions
  • Operating current approximately 150 mA; operating temperature range 0–70 °C (commercial grade)
  • Supports FBCP software driver for setting software resolution and dual-screen display

Commands and examples – verify before use:  

sudo apt-get install unzip -y
sudo apt-get install cmake -y
wget https://files.waveshare.com/wiki/common/Waveshare35a.zip
unzip ./Waveshare35a.zip
sudo cp waveshare35a.dtbo /boot/overlays/
sudo nano /boot/firmware/config.txt
dtparam=spi=on
dtoverlay=waveshare35a
hdmi_force_hotplug=1
max_usb_current=1
hdmi_group=2
hdmi_mode=87
hdmi_cvt 480 320 60 6 0 0 0
hdmi_drive=2
display_rotate=0
export FRAMEBUFFER=/dev/fb1
startx 2> /tmp/xorg_errors
sudo nano /usr/share/X11/xorg.conf.d/99-fbturbo.~
Section "Device"
Identifier "Allwinner A10/A13 FBDEV"

Notes and version constraints

  • The source text contains placeholders such as {{{name2}}} and {{{userDefinedInfo}}}; these were ignored.
  • Exact pin mappings must be verified during connection; incorrectly wired pins can cause malfunctions.
  • Configuration varies by OS version (Trixie, Bookworm, Bullseye); steps are version-sensitive.
  • Automatic CLI login requires the username to be 'pi'; otherwise auto-login will not work.
  • After completing all configurations, system restart takes longer and SSH requires a moment before becoming available.
  • If touch response is slow, the anti-jitter delay in the 99-calibration.conf file can be adjusted, but this may reduce touch accuracy.

Source and revision record

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