M5Paper EPD power consumption



  • @tatar-andrei said in M5Paper EPD power consumption:
    ... and without any previous state (unless written to FLASH/SD)...

    you can also save data into M5Papers EEPROM (FM24C02 - 2K-bit(256x8)-EEPROM) during shutdown.

    Thanks
    Felix



  • @fonix232 said in M5Paper EPD power consumption:

    battery cutoff voltage for charging seems to be 4.2V

    Hello @fonix232

    I also thought the charger is only set for 4.2V cutoff voltage due to the fact that the charger IC in the M5Paper schematics is marked as SLM6600. However the charger IC in my M5Paper actually is a SLM6635 which by default has a charging termination voltage of 4.35V according to its data sheet.

    Thanks
    Felix



  • @felmue then how do you explain that charging voltage is 4.35V until the battery reaches 4.2V, when the charging voltage drops to 4.2V as well?



  • Hello @fonix232

    a very good question indeed to which I don't have an explanation (yet).

    Another question is how accurate the voltage reported by the ESP32 ADC actually is. There also is a voltage divider and some SCALE factor in the factory test firmware. Interestingly the SCALE factor seems to have changed over time:

    #define SCALE 0.5//0.78571429
    

    Just curious - did you also verify the battery voltage with a multimeter directly connected to the battery?

    Thanks
    Felix



  • Hi guys

    today I did a charging experiment with a fully depleted M5Paper battery. After about 2 hours the charger IC switched from charging to standby (according to the two LEDs I've soldered to the corresponding charger IC outputs).

    I used a multimeter (connected directly to the battery) to measure the battery voltage. The voltage from the internal ADC, read via M5.getBatteryVoltage(), was about 5% higher than the voltage read by the multimeter for voltages below 4.2V. Above that the two values were pretty close. The reason for that is the voltage divider (3k / 11k) which when fed with 4.2V produces about 3.3V to the ADC input which is about the maximum a GPIO can take.

    The highest voltage I've seen on the multimeter was 4.31V before the charging stopped. After which the voltage dropped back to 4.25V. I think that means the charger IC actually is setup for a 4.35V battery, but for some reason doesn't go all the way up to 4.35V.

    Update: a possible reason is explained in the datasheet (Google translated):

    ==========
    _______________Charge termination voltage setting The default full termination voltage V FLOAT set inside the chip is approximately 4.35V, but due to the large charging current, the internal resistance of the battery and the line Loss will cause the actual full-charge termination voltage to be lower than this value, resulting in battery failure The law is full enough. SLM6635 by an external resistor RPV to increase V FLOAT of Voltage, used to compensate various losses, or to satisfy different applications Special requirements for voltage.The compensation voltage can be calculated by the following formula:

    Delta V = I bat (Standby mode) * RPV

    If there is no need to compensate the V FLOAT voltage, it is recommended that RPV be set to 1kΩ.

    ==========

    Thanks
    Felix



  • @tatar-andrei said in M5Paper EPD power consumption:

    I did play around more with power down states and I managed to get a light sleep mode with fast wakeup from touch at around ~9mA.

    Hello @tatar-andrei

    I tried to get the touch into sleep mode by applying the steps outlined in the GT911 programming guide but I don't see any reduction in power consumption.
    The steps are:

    • switch ESP32 interrupt GPIO from input to output and set it low
    • issue command 0x05 to address 0x8040

    is there anything else that needs to be done? I'd appreciate your insight on that.

    Thank you very much in advance.

    Cheers
    Felix



  • @tatar-andrei said in M5Paper EPD power consumption:

    months on a battery charge"

    registered a new account for replying this.. not currently a M5Paper owner but will buy one soon!
    I happened to be involved in a ESP + 8951 epaper project months ago, the target is months on battery charge (3xAAA battery).
    Main env is done using arduino, and scriptable via Lua. UI is rendered on server, send down to the device during idle & stitched with Lua (it's a calendar kind of device).

    repo is @ https://github.com/luan007/em_playbook
    hope some code / impl provides some reference ..



  • Hi guys

    I just discovered that the voltage divider used to feed the battery voltage into the ADC uses different values from what's listed in the M5Paper schematic.

    • M5Paper schematics: 3 kOhm and 11 kOhm -> factor: 0.78571428571
    • found in my M5Paper: 10 kOhm and 10 kOhm -> factor: 0.5

    With the actual values the modified SCALE factor (0.785.. -> 0.5) found in the library also makes more sense. It compensates the voltage divider.

    BTW: when you feed 4.2 V into the original 3 kOhm / 11 kOhm voltage divider you get exactly 3.3 V. So I guess initially M5Paper was designed / planned to use a 4.2 V battery.

    Cheers
    Felix



  • Hi guys

    I think I found the reason for why the touch IC (GT911) did not react when I tried to put it into sleep mode. The procedure asks for the ESP32 GPIO used for the touch interrupt to change to an output and then be driven low by the ESP32. Unfortunately GPIO36 is used for the touch interrupt and that is one of the few GPIOs which can only be used as input. So without hardware modification I don't see a way to put the touch IC into sleep mode. Or am I missing something?

    Thanks
    Felix



  • @felmue that definitely sounds like a massive design issue - I wonder, maybe that's why the M5EPD library doesn't have any touchscreen power-off calls?

    There was also a post on the M5Stack twitter recently, showing a blurred out image of upcoming devices, with a device eerily similar to the M5Paper taking up a large chunk of the photo: https://twitter.com/M5Stack/status/1357559621389479940/photo/1

    I wonder if the design team realised these small issues and made a new board that is more fit for general usage purposes. It happened with the M5Cores (the Basic model had no PSRAM and the first units only had 4MB storage, which later got expanded to 16MB, then the Grey kit came with an MPU, then the Fire kit also included a microphone and PSRAM, among other changes), though the speed is much faster - I think there was almost a year between the Basic and Grey M5Cores, whereas the M5Paper was only recently released.

    It does feel like a slap in the face for us who already bought multiple M5Paper units though - we've received a device that has a handful of obvious faulty design choices, and now we have to buy the new, updated model to get functionality that should've been working in the first iteration. Don't get me wrong, I'm happy for the updated design, I just hope there will be some discount for those who've already got units on their hands.