M5Paper EPD power consumption

  • @felmue
    I did a summary of the 3 ports A, B and C
    You made a good choice using GPIO19.
    Indeed, welding work is simplified.
    Do you share your source code?

  • Hello @bricox

    @bricox said in M5Paper EPD power consumption:

    Do you share your source code?

    Sure, you can find my touch sleep mode test sketch here.

    It's a extended version of the TOUCH example which uses the left/up button to set touch into normal mode and right/down button to set into sleep mode.


  • @felmue
    To fully understand the GT911 controller, download these 2 pdf

    Several developments are desirable :

    • read position under interrupt and not in polling mode [GT911::update()]
    • Exploit more all modes
    • Check if the "green mode" (3.3mA) automatically change after 1 second of inactivity
    • Generate a sound when you touch it

    List of 21 other GT911 drivers :
    including one in cpp:

  • @bricox based on the documentation, it should be possible to set the touch panel in a gesture recognising mode - would be nice to be able to offload that from the ESP32, alongside the interrupt-instead-of-poll change. This would certainly improve battery life.

  • Hello guys

    @bricox - thank you for the links. I appreciate it. I already had the programming guide, but not the datasheet.

    @fonix232 - so far I have not tried the gesture mode.

    I am curious about what you guys are going to find regarding other modes.


  • Hello guys .... @felmue, @fonix232, @tatar-andrei... and other enthusiasts ....

    I have others links for the GT911 driver in cpp
    With interrupt : https://github.com/nik-sharky/arduino-goodix/blob/master/Goodix.cpp
    No interrupt but handles 5 fingers : https://github.com/caiannello/ER-TFTM0784-1/blob/master/src/touch.cpp

    We’ll have to adapt these source codes.

    Sorry, i'm not a specialist for interrupts of Arduino framework....I am more familiar with the HAL framework of the STM32.

    Thank you for these sustained sharing

  • hello,

    a little bit of electronics (because no present in official doc) :

    The PFL with C1, C2, C3, C4 R1 and C5:
    Remark : pin 7&8 are "shield"

  • Hello @felmue

    Find 1 output, to put low the INT signal of GT911, have another way possible ....
    In the ESP pdf, I found this :
    For reuse these pins, an article : https://www.instructables.com/ESP8266-Using-GPIO0-GPIO2-as-inputs/
    I think that, in the M5paper, we can use GPIO0 as output.
    What you think about ?

  • Hello @bricox

    in M5Paper GPIO0 (together with ESP32_EN) already is connected to the boot / download mechanism which is controlled by CP_RTS and CP_DTR from the USB chip. ESP32_EN is also connected to the touch reset line which together with the touch INT line determine which I2C address the touch IC is going to use.

    If you also connect GPIO0 to the touch INT line, GPIO0 and ESP32_EN will not only determine the ESP32 boot mode but also the touch IC I2C address depending on what CP_RTS and CP_DTR are doing.

    On the other hand controlling GPIO0 from code to put the touch IC into sleep mode might have a negative effect on the automatic boot / download mechanism.

    I personally would leave GPIO0 alone, but in general it is correct that GPIO0 can be used as output if needed.


  • Hello @felmue,

    While I was commenting on the source code, I found un bug in the GT911 driver :
    _fingers[] can be indexed up to 5
    In declaration, _fingers[] can be indexed up to 2

    In addition, it would be elegant to use bit fields for describing registers that have specific functions.
    An example : 0_1615984402868_5b228515-423f-44aa-ad3a-d75715da83e9-image.png

  • Structure

    typedef struct reg814E_s {		// 
     union {						// same location of 2 fields of 1 byte
       uint8_t reads;				// this byte
       struct {					// field bits of this byte
         uint8_t touchPts  : 4;	// b0 to b3 : number of touch points
         uint8_t haveKey   : 1;	// b4 : HaveKey
         uint8_t proxi     : 1;	// b5 : Proximity Valid
         uint8_t largeDet  : 1;	// b6 : large detect
         uint8_t status    : 1;	// b7 : buffer status
    } __attribute__((packed)) reg814E_t;	// minimize memory alignment

    or simpler writing

    typedef struct {
      union {              // same location of 2 fields of 1 byte
        uint8_t reads;     // this byte
        struct {           // field bits of this byte, starting with low weight
            touchPts  : 4, // b0 to b3 : number of touch points
            haveKey   : 1, // b4 : HaveKey
            proxi     : 1, // b5 : Proximity Valid
            largeDet  : 1, // b6 : large detect
            status    : 1; // b7 : buffer status
    } reg814E_t;


        bool _is_finger_up = false;
        uint8_t _num = 0;
        uint8_t _rotate = ROTATE_0;
        tp_finger_t _fingers[2];
        reg814E_t r814E;
        uint8_t _iic_addr = 0x14;
        uint8_t _pin_int = -1;
        bool _sleeping = false;

  • Use :

    void GT911::updateB()						// as update but modify by Bricox ...
        r814E.reads = read(0x814E);				// "read struct" AND these 5 explicite bits fields
            if(r814E.touchPts != 0)
                _is_finger_up = false;
                _num = r814E.touchPts;			// "_num" could be definitively replaced by "r814E.touchPts"
                uint8_t data[num * 8];
                read(0x8150, data, _num * 8);	// read block of all fingers , up to 5*8 bytes
                for(int j = 0; j < _num; j++)	// for each finger
                    uint8_t *buf = data + j * 8;// address base of each finger

    Sorry, comments that were aligned, in my notepad++ by multiple Tabs, are no longer aligned in the snippets viewer

  • The power consumption you're observing on your M5Paper when the EPD (Electrophoretic Display) is idle is indeed higher than expected. It's unlikely that you have a defective unit, as the behavior you described is more likely related to software or driver optimization.

    EPD displays typically have low power consumption because they require power only during screen updates. Once the image is displayed, the EPD consumes very little power to maintain the image. However, it's possible that the EPD driver or the default app on your M5Paper is not optimized for low power consumption during idle periods.

    To optimize the EPD power consumption during idle periods, you could try the following steps:

    Check for firmware updates: Ensure that you have the latest firmware version for your M5Paper. Manufacturers often release firmware updates that include optimizations and bug fixes that can improve power efficiency.

    Look for power-saving options: Check if there are any power-saving options available in the EPD driver or the default app settings. Some devices offer options to reduce the refresh rate or enable power-saving modes for the EPD.

    Consider customizing the EPD driver: If you have experience with programming and access to the EPD driver source code, you can explore the possibility of customizing the driver to optimize power consumption during idle periods. This might involve tweaking the refresh mechanism or implementing additional power-saving features.

    It's worth noting that while EPD displays are generally power-efficient, power consumption can vary depending on factors like display size, color depth, and the specific implementation of the EPD driver. Therefore, it's not uncommon to encounter variations in power consumption between different devices or even different firmware versions.

  • The E-Ink Paper Display (EPD) on the M5Paper consumes power even when the screen is idle due to its underlying technology. E-Ink displays are different from traditional LCD or OLED screens in that they only consume power when the content on the screen is changed. Once an image or text is displayed on an E-Ink screen, it doesn't require any power to maintain that state. However, changing the content on the screen, such as refreshing to display a new image or text, does consume power.

    In your case, when the EPD power is disabled, the display is essentially turned off, and it consumes very little to no power because it's not actively refreshing the content. When you enable the EPD power and the display is idle, it's likely in a state where it's ready to receive new content and is therefore consuming some power in anticipation of a refresh.

    The power consumption you're observing is not necessarily a sign of a defective unit but rather a characteristic of E-Ink displays. If you want to optimize power consumption further for your low-power application, you might consider:

    Reducing Refresh Rate: Minimize the frequency of screen refreshes. E-Ink displays are typically used in applications where the content doesn't change frequently. You can adjust the refresh rate to be as infrequent as possible to save power.

    Full Screen Updates: Instead of partial screen updates, use full screen updates when you need to change the content. Partial updates can be more power-intensive.

    Deep Sleep: Continue using the deep sleep mode of the ESP32 when the screen is idle. This will significantly reduce overall power consumption.

    Optimize Code: Make sure your code is efficiently managing the display and other peripherals. Ensure that you are properly putting the ESP32 into deep sleep mode when it's not actively needed.

    Hardware Modifications: Depending on your specific use case, you might consider hardware modifications to further reduce power consumption. This could involve custom power management circuitry or using different power supplies.