RAK811 Break Board detect external power



  • Hi everyone,

    Any Idea how to detect external (read USB) power? I have a car tracker which gets power from USB during ignition on and from the LiPo when battery off.
    How can I detect this (as I want to set the GPS to low power and change the send interval of LoRa-packages during battery operation.
    My idea was to use the TX from CP2102, but unfortunately, the CP2102 is powered in battery mode (btw: why? I dont need RS232<->USB if I have no USB connection...).
    Any other ideas without hardware mod?
    Regards, Edi


  • administrators

    We are making changes to the hardware design of the RAK811 Tracker to reduce the power consumption of the equipment. Can you summarize some of your opinions?



  • Hallo rakadmin :)

    Well, I have some ideas how to reduce the power:

    • Obiously, the red LED needs a lot of current and is not really needed. I always unsolder it. Maybe you can connect it via a solder jumper so it's easy to deactivate it. This picture shows what i mean:
      0_1527759405551_jumpers.jpg

    • It would be great if V_BCKP is not hard wired to GPS_3V3. If you turn of the GPS current by PA15, it takes up to 40 seconds until the GPS signal is available again using about 17mA in this time. You cold connect it to a GPIO (it only takes about 20uA) or even better, make it selectable between VCC3.3V and a GPIO, also via solder jumper.
      0_1527759837061_RAK811_GPS_V_Backup.png

    • Remove to connection from VCC3.3 to the VDD pin of the CP2102. First we save current as we don't need to power the CP2102 when we have no USB connection. On the other hand, we can use PA10 to detect if we are USB-powered or battery powered, so we can switch sending rates and power saving options (deinit UART1, put GPS to low power mode or switch it off until we detect an interrupt from the LIS3DH and so on).
      0_1527760458229_RAK811_ CP2102.png

    Thank you for your considerations!
    Regards, Edi


  • administrators

    Thank you very much for your suggestion. Your suggestion is very valuable.



  • @rakadmin You're very welcome. It's nice to see how your company cares about the customer wishes!



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