How to turn off screen completely

[bbokser]

Users discovered that the original M5StickC would not save a significant amount of power by setting screen brightness to the minimum. Completely shutting off screen power draw required some low level hacks demonstrated here.

The M5StickCPlus2 does not use the AXP192, so this trick doesn't apply. So I am wondering what the new trick is, if anything. Does StickCP2.Display.setBrightness(0) really minimize screen power draw or is there more that I can do?

[Thomascountz]

From what I can tell, StickCP2.Display.setBrightness(0) reduces brightness but doesn’t fully cut power to the display. The M5StickCPlus2 uses an ST7789, so you're right that the old AXP192 workaroudns won’t work.

Looking at the M5GFX library (the one linked in this M5StickCPlus2 library), there seems to be a few ways to cut power further:

// https://github.com/m5stack/M5GFX/blob/master/src/lgfx/v1/LGFXBase.hpp#L1422-L1426

inline void sleep(void) { _panel->setBrightness(0); _panel->setSleep(true); }
inline void wakeup(void) { _panel->setSleep(false); _panel->setBrightness(_brightness); }
inline void powerSave(bool flg) { _panel->setPowerSave(flg); }
inline void powerSaveOn(void) { _panel->setPowerSave(true); }
inline void powerSaveOff(void) { _panel->setPowerSave(false); }

1. sleep()

The sleep() method calls Panel_LCD.setSleep(true), sending CMD_SLPIN to the ST7789, which the datasheet describes on pg. 182:

• This command causes the LCD module to enter the minimum power consumption mode.
• In this mode the DC/DC converter is stopped, internal oscillator is stopped, and panel scanning is stopped.
• MCU interface and memory are still working and the memory keeps its contents.

2. powerSaveOn

There’s also a way to call the Panel_LCD.setPowerSave(true) method, which sends CMD_IDMON (idle mode on), described on pg. 222:

• This command is used to enter into Idle mode on.
• There will be no abnormal visible effect on the display mode change transition.
• In the idle on mode,
  • 1. Color expression is reduced. The primary and the secondary colors using MSB of each R,G and B in the Frame Memory, 8 color depth data is displayed.
  • 2. 8-Color mode frame frequency is applied

I haven't tried this myself, but it seems like sleep() is the way to go to reduce power consumption the most.

References:

https://github.com/m5stack/M5GFX/blob/b2422cdb4735159209c2097d425c0756505b9a81/src/lgfx/v1/LGFXBase.hpp#L1422-L1426

https://github.com/m5stack/M5GFX/blob/b2422cdb4735159209c2097d425c0756505b9a81/src/lgfx/v1/panel/Panel_LCD.cpp#L100-L114