M5.begin(0,1,1);
M5.Axp.SetLDO2(false);
M5.Axp.SetLDO3(false);

I did a simple test: with only REG 28H the screen stays slightly warm. With both 28H and 10H, the screen cools off after a while. Hardly a scientific test, I know, but seems to point to the need to set both registers.

I'm looking at this thread to hopefully implement a complete screen turn off, but am not sure what register mask to use (based on quoted post)

Here is what I have, the screen is off but hard to know if the screen has actually been disabled.

void turnOffScreen() {
Wire1.beginTransmission(0x34);
Wire1.write(0x10);
Wire1.write(0b00000000); // 7-3=? | 2=EXTEN | 1=? | 0=DC-DC2
Wire1.endTransmission();

Wire1.begin(21, 22);
Wire1.beginTransmission(0x34);
Wire1.write(0x12);
Wire1.write(0b01001011); // 7=? | 6=EXTEN | 5=? | 4=DC-DC2 | 3=LDO3 | 2=LDO2 | 1=DC-DC3 | 0=DC-DC1
Wire1.endTransmission();

Wire1.beginTransmission(0x34);
Wire1.write(0x28);
Wire1.write(0b00001111); // 7-4=LDO2 | 3-0=LDO3
Wire1.endTransmission();
}

@ws1088 Funny enough I bought my M5StickC with the watch strap and all, but not because I wanted a watch – I don't wear them – but because it enables me to tie it up to my backpack when I do LoRa range tests :-)

why would you use m5stickc to do LoRa range tests? You can get LoRa chip with OLED screen. Do you connect m5stickc to a LoRa chip via I2C? or WiFi AP?

How are you getting 5 hours of life? it seems you would need <16 ma total drain

Are you sleeping the ESP32?

void AXP192::ScreenBreath(uint8_t brightness) {
  Wire1.beginTransmission(0x34);
  Wire1.write(0x28);
  Wire1.write(((brightness & 0x0f) << 4)); //Enable LDO2&LDO3, LED&TFT 3.3V
  Wire1.endTransmission();
}

What it does is it takes the value you passed, cuts it to 4 bits (0-15) and moves those 4 bits to bits 4-7. Register 28H is voltage control for LDO2 (bits 4-7) and LDO3 (bits 0-3). So the OLED is connected to LDO2.

What that 0-15 value represents is a voltage of 1.8 to 3.3V, in 100mV/steps. So M5.Axp.ScreenBreath(0); sets voltage to 1.8V, and M5.Axp.ScreenBreath(15); to 3.3V. Not what we really want – as the goal was to set voltage to zero... :-)

Whereas register 12H controls the state (ON/OFF) of a bunch of wires, including LDO2 (bit 2). Hence the code above.

Wire1.beginTransmission(0x34);
Wire1.write(0x12);
Wire1.write(0b01001011);  // LDO2, aka OLED_VDD, off
Wire1.endTransmission();

This turns off LDO2, and thus the backlight. To turn it back on:

Wire1.beginTransmission(0x34);
Wire1.write(0x12);
Wire1.write(0x4d); // Enable LDO2, aka OLED_VDD
Wire1.endTransmission();

void AXP192::begin(void) {
  Wire1.begin(21, 22);
  Wire1.beginTransmission(0x34);
  Wire1.write(0x10);
  Wire1.write(0xff);  //OLED_VPP Enable
  Wire1.endTransmission();
  Wire1.beginTransmission(0x34);
  Wire1.write(0x28);
  Wire1.write(0xff); //Enable LDO2&LDO3, LED&TFT 3.3V
  Wire1.endTransmission();

A peek at the datasheet says that REG 28H is power management for LD02 and LD03. Sure thing. That's what the comment in the code above says – along with a hint that LD03 is for the TFT.

Meanwhile, REG 10H is two ON/OFF switches, for EXTEN and DC-DC2 – commented in the code as VPP_Enable. Bueno.

I am not sure which of EXTEN or DC-DC2 is connected to the OLED (both?), but turning either or both off will cut off the current to the OLED.

Moreover there's this code later:

  Wire1.beginTransmission(0x34);
  Wire1.write(0x12);
  Wire1.write(0x4d); //Enable DC-DC1, OLED_VDD, 5B V_EXT
  Wire1.endTransmission();

And REG 12H seems to do more of the same as 10H:

Bit 3 turns ON/OFF LD03, which, as we saw above, is supposed to be the OLED. Good odds that setting bit 3 of REG 12H to zero would work too.

I don't have time to test it now, but I'll try later tonight.

brightness	TFT backlight brightness (range: 7~15)

• ScreenBreath(15): 0.20A
• ScreenBreath(12): 0.17A
• ScreenBreath(10): 0.15A
• ScreenBreath(7): 0.14A
• ScreenBreath(0): 0.14A