Why can't the backlight be completely turned off while sleeping?

[Quency-D]

The heltec-v4-tft uses the tft firmware 2.7.15 MUI. I found that even after the screen has been naturally off for 7-8 hours, the screen still has backlighting. After disassembling the board and checking the backlight pin waveform with an oscilloscope, I found that it wasn't fully pulled low, but rather had a negative duty cycle of 99.x%, resulting in a faint glow on the screen.

I tested in the Arduino by changing the positive duty cycle of its PWM to 0, and found that the backlight could be completely turned off.

I'm trying to find the location in the device-ui where the positive duty cycle can be changed to 0, but I'm unsure if this is intentionally designed so that it cannot be changed to 0.

[Quency-D]

I tried adding code to set the brightness to 0 in the following location, and found that it completely turns off the backlight during sleep and allows normal wake-up. However, this location doesn't seem to be the most suitable. I'll take another look.

lgfx->setBrightness(0);

template <class LGFX> void LGFXDriver<LGFX>::task_handler(void)
{
    // handle display timeout
    if ((screenTimeout > 0 && lv_display_get_inactive_time(NULL) > screenTimeout) || powerSaving ||
        (DisplayDriver::view->isScreenLocked())) {
        // sleep screen only if there are means for wakeup
        if (DisplayDriver::view->getInputDriver()->hasPointerDevice() || hasTouch() ||
            DisplayDriver::view->getInputDriver()->hasKeyboardDevice() || hasButton()) {
            if (hasLight()) {
                if (!powerSaving) {
                    // dim display brightness slowly down
                    uint32_t brightness = lgfx->getBrightness();
                    if (brightness > 1) {
                        lgfx->setBrightness(brightness - 1);
                    } else {
                        ILOG_INFO("enter powersave");
                        lgfx->setBrightness(0);
                        DisplayDriver::view->screenSaving(true);
                        if (hasTouch() && hasButton()) {
                            ILOG_DEBUG("disable touch, enable button input");
                            lv_indev_enable(DisplayDriver::touch, false);
                            lv_indev_enable(InputDriver::instance()->getButton(), true);
                        }
                        lgfx->sleep();
                        lgfx->powerSaveOn();
                        powerSaving = true;
                    }

[Quency-D]

I think this is a good way to change it. What do you think? @mverch67

if (brightness > 1) --> if (brightness > 0)

template <class LGFX> void LGFXDriver<LGFX>::task_handler(void)
{
    // handle display timeout
    if ((screenTimeout > 0 && lv_display_get_inactive_time(NULL) > screenTimeout) || powerSaving ||
        (DisplayDriver::view->isScreenLocked())) {
        // sleep screen only if there are means for wakeup
        if (DisplayDriver::view->getInputDriver()->hasPointerDevice() || hasTouch() ||
            DisplayDriver::view->getInputDriver()->hasKeyboardDevice() || hasButton()) {
            if (hasLight()) {
                if (!powerSaving) {
                    // dim display brightness slowly down
                    uint32_t brightness = lgfx->getBrightness();
                    if (brightness > 0) {
                        lgfx->setBrightness(brightness - 1);
                    } else {
                        ILOG_INFO("enter powersave");
                        DisplayDriver::view->screenSaving(true);
                        if (hasTouch() && hasButton()) {
                            ILOG_DEBUG("disable touch, enable button input");
                            lv_indev_enable(DisplayDriver::touch, false);
                            lv_indev_enable(InputDriver::instance()->getButton(), true);
                        }
                        lgfx->sleep();
                        lgfx->powerSaveOn();
                        powerSaving = true;
                    }

[mverch67]

I think this is a good way to change it. What do you think? @mverch67

if (brightness > 1) --> if (brightness > 0)

yes, sounds reasonable, thanks.