Graphical User Interface on the IoT node

Introduction

The 2.4 " display has a pixel resolution of 320x240 pixels. It is controlled by an ili9431 display driver and provides a touch screen based on the xpt2046 controller. Information about the display and its pin-outs can be found at https://docs.wemos.cc/en/latest/d1_mini_shield/tft_2_4.html.

With a high resolution screen and a touch screen the display can be used to provide a local Graphical User Interface (GUI) for your IoT project.

Hardware preparation

The Lolin 2.4" display uses the following pinout:

TFT board function	CPU Pin
TFT_LED	NC* (D1,D2,D3,D4)	(GPIO 22, GPIO 21, GPIO 17(WROOM) or GPIO 25 (WROVER), GPIO 16 (WROOM) or GPIO 4 (WROVER))
TFT_RST	RST* (D1,D3,D4)	(GPIO 22, GPIO 17(WROOM) or GPIO 25 (WROVER), GPIO 16 (WROOM) or GPIO 4 (WROVER))
TFT_DC	D8	GPIO 5
MOSI	D7	GPIO 23
MISO	D6	GPIO 19
SCK	D5	GPIO 18
TFT_CS	D0	GPIO 26
TS_CS	(D1,D2,D3*,D4)	(GPIO 22, GPIO 21, GPIO 17(WROOM) or GPIO 25 (WROVER), GPIO 16 (WROOM) or GPIO 4 (WROVER))

The pins in brackets can be jumpered with solder jumpers and the "*" shows the default jumper settings. As GPIO 16 and GPIO 17 cannot be used on the WROVER and are in fact not connected to the D3 and D4 pins we must short-circuit GPIO 25 with GPIO 17 and in case GPIO 16 is used we short-circuit GPIO 4 with GPIO 16. In order to drive the pins GPIO 4 and 25 will then be used in the program.

New pin defaults

I modified the ili9431 driver for lvgl (lib/lv_bindings/drivers/esp32/ili9XXX) to reflect the above pin-outs:

miso=19, mosi=23, clk=18, cs=26, dc=5, rst=-1, power=-1, backlight=-1, spihost=esp.VSPI_HOST, mhz=40, factor=4, hybrid=True

A graphical user interface library lvgl has been developed in C and is now available with a MicroPython binding, such that the library structs and functions are available in MicroPython. In order for this to work we need a modified !MicroPython binary with lvgl and the lv_bindings included in the code. The original lvgl documentation is available at https://docs.lvgl.io/v7/en/html/intro/index.html.

The same text but adapted to the MicroPython binding will be available on this TWiki (currently under development)

-- Uli Raich - 2020-10-23

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