TFT screen not working on Rpi A+

Question

I have an old TFT LCD SPI screen, which I believe uses ILI9341 and would like to use it on my (old) RPi A+. Unfortunately, it just stays blank. I am not even sure it is working... My RPiA+ has a fresh Raspbian Stretch.

I have wired my screen following this blog and using this pin layout. Just in case I haven't understood correctly:

• I have wired VIN of the screen to 3.3 VDC power on the Pi (pin 1)
• I haven't wired MISO and SDCS: my understanding is that they are for the SD card on the screen - which I do not use
• The LED is my case is wired to GPIO 2
• MOSI goes to "MOSI SPI GPIO 12"
• SCK goes to "SCLK SPI GPIO 14"
• CS goes to CE0 SPI GPIO 10
• D/C goes to GPIO 24
• RST goes to GPIO 25
• GND goes to ground

I tried to load the driver fb_ili9341, but this isn't supported:

$ sudo modprobe fbtft_device name=fb_ili9341 gpios=reset:25,dc:24,led:2 speed=16000000 rotate=90 bgr=1
modprobe: ERROR: could not insert 'fbtft_device': Invalid argument

I listed the available modules with sudo modprobe fbtft_device name=list; dmesg | tail -30 and there was only one ili drivers: ili9481, so I decided to use that one (but I am not sure this is correct).

So, I tried again:

$ sudo modprobe fbtft_device custom width=320 height=240 name=ili9481 gpios=reset:25,dc:24,led:2,cs:10 speed=16000000 rotate=90 bgr=1

This loads correctly as we see in dmesg:

$ dmesg
...
 2229.934312] graphics fb1: fb_ili9481 frame buffer, 240x320, 150 KiB video memory, 4 KiB buffer memory, fps=20, spi0.0 at 16 MHz
[ 2229.934512] fbtft_device: GPIOS used by 'ili9481':
[ 2229.934524] fbtft_device: 'reset' = GPIO25
[ 2229.934530] fbtft_device: 'dc' = GPIO24
[ 2229.934536] fbtft_device: 'led' = GPIO2
[ 2229.934542] fbtft_device: 'cs' = GPIO10
[ 2229.934562] spidev spi0.1: spidev spi0.1 125000kHz 8 bits mode=0x00
[ 2229.934578] fb_ili9481 spi0.0: fb_ili9481 spi0.0 16000kHz 8 bits mode=0x00

Then, according to the blog, I used con2fbmap 1 1 to redirect the console to my screen. It remains totally blank.

Also, I have enabled SPI in raspi-config.

So my questions are:

1. Is my wiring correct?
2. Is the driver I am using correct, and if not, which one should I use. There is no specific indication on the device itself...
3. Is there a way to test if my screen is still working or damaged? SHould a LED be lighting up? (can't see one)
4. If it is functional, Why isn't it showing anything?

Thanks !

Answer 1

There were 2 issues:

1. The Invalid argument in my modprobe does not mean ili_9431 is not supported, but that my command has an invalid argument. ili_9431 is supported. It seems that the keyword custom is mandatory. So the right command should be sudo modprobe fbtft_device custom name=fb_ili9341...
2. The GPIOs I used in my command line were wrong. To find the correct numbering of GPIOs for a given model of Raspberry Pi, I recommend using the command pinout which is from gpiozero. In my case, the correct values were gpios=reset:26,dc:19,led:27.

So, the full command is: sudo modprobe fbtft_device custom name=fb_ili9341 gpios=reset:26,dc:19,led:27 speed=16000000 rotate=90 bgr=1. As soon as this command is launched the LED on the screen lights up.

Note that fbtft_device does not need to be downloaded or installed on current Raspbian versions, it's already there.