TFT_BACKLIGHT_ON not used in ST7789 and settings seem opposite those I'm testing with and are working

[ljunquera]

I am trying to work with the ST7789 but am wondering why the TFT_BACKLIGHT_ON setting is not used. I see in the driver's init file I see this in two places:

#ifdef TFT_BL
  // Turn on the back-light LED
  digitalWrite(TFT_BL, HIGH);
  pinMode(TFT_BL, OUTPUT);
#endif

In my code, just testing the backlight, this makes it turn on:
digitalWrite(TFT_BL, LOW);
and this makes it turn off:
digitalWrite(TFT_BL, HIGH);

A lot of the other drivers use it. I also see this code in the TFT_eSPI.cpp:

#if defined (TFT_BL) && defined (TFT_BACKLIGHT_ON)
  pinMode(TFT_BL, OUTPUT);
  digitalWrite(TFT_BL, TFT_BACKLIGHT_ON);
#else
  #if defined (TFT_BL) && defined (M5STACK)
    // Turn on the back-light LED
    pinMode(TFT_BL, OUTPUT);
    digitalWrite(TFT_BL, HIGH);
  #endif
#endif

Does this override the driver settings?

[Bodmer]

Different displays have different arrangments for the backlight. Some displays have a transistor that can be used to switch the backlight on and off. The majority of displays do not have a backlight that is controlled via the display data/command interface. Some displays require power to be applied to the backlight signal. (e.g 3.3V or 5V).

[ljunquera]

If that's the case shouldn't the ST7789_init.h driver have a TFT_BACKLIGHT_ON setting vs hard coding HIGH:

#ifdef TFT_BL
  // Turn on the back-light LED
  digitalWrite(TFT_BL, HIGH);
  pinMode(TFT_BL, OUTPUT);
#endif

should be this:

#ifdef TFT_BL
  // Turn on the back-light LED
  digitalWrite(TFT_BL, TFT_BACKLIGHT_ON);
  pinMode(TFT_BL, OUTPUT);
#endif

[ljunquera]

I'm curious why this would not be an issue given there is a fix requested to the ST7789_Init.h to support different displays which have different arrangements for the backlight driver using the TFT_BACKLIGHT_ON, as opposed to a discussion topic?

[Bodmer]

There is legacy code in the ST7789_init.h driver. You can delete it if you wish.

[ljunquera]

So the two places the ST7789_init.h driver where this code exists should be deleted:

#ifdef TFT_BL
  // Turn on the back-light LED
  digitalWrite(TFT_BL, HIGH);
  pinMode(TFT_BL, OUTPUT);
#endif