Random brown outs, screen flickering, and possible solutions

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    User avatar
    LattePanda
    Site Admin
    Posts: 2555
    Joined: Wed Jan 20, 2016 9:09 am

    Fri Sep 02, 2016 10:28 am

    I have been trying to replicate some of the issues posted on the forum relating to random brown outs, i.e shutting off unexpectedly and screen flickering.
    Some of these random shutoffs are down to the cherrytrail hitting a thermal threshold and shutting down (an inbuilt safety precaution of the cherrytrail), however, some issues are related to voltage drop as a result of having the 7" screen attached to the mipi connector. obviously as the screen has no external power source it is drawing power from the board itself.
    viewing the panda through an hdmi output or a vnc server should not require extra voltage.

    here are some experiments i did:

    my setup:
    using the 7" screen attached to the panda though mipi interface.
    I have used a bench power supply and and powering the panda using the CN2 headers using F dupont wires
    amp draw is about 0.8a - 1a

    NOTE: if you try to replicate this, please note that the panda can handle up to 6v but it is not advisable to go beyond this, *AS YOU WILL FRY YOUR BOARD*

    problem: screen flickering
    reason: screen is receiving insufficient voltage
    solution: increasing voltage to 5.3 - 5.5v has it running stable

    problem: lattepanda powers off in bios before booting in to windows
    reason: board is not receiving insufficient voltage and browning out
    solution: 5.5v - successful boot

    problem: windows boots, but browns out when i click start
    reason: board is not receiving insufficient voltage as processor voltage spikes and is browning out
    solution: 5.5v - ok as long as screen is not at full brightness
    if screen is at full brightness, 5.7v has it running stable

    conclusion: if you have the screen connected, you will probably need slightly more than 5v



    hope this can point someone in the right direction!
    Enjoy Tinkering with LattePanda ! :lol:

    User avatar
    Boring
    Posts: 88
    Joined: Sat Apr 16, 2016 7:14 pm

    Sat Sep 03, 2016 10:37 am

    Thanks for the tips. Do you have any suggestions on how to increase voltage if you Are using a lipo battery?

    User avatar
    KevinA
    Posts: 44
    Joined: Fri Sep 02, 2016 8:54 pm

    Sat Sep 03, 2016 4:41 pm

    Where did you find the CN2 reference? So far I have only found one web page with no detailed information,their DOC page. At the bottom of that page they list all the power supplies they have 'tested' with links, most of those supplies are for QC phones with triple power levels, 5,9,12 volt. I'm running a 12 volt 5 amp supply through a step down converter (not adjustable) that outputs 4 amp to a USB Host connector. I can use the USB cable off my QC Galaxy Note or I did find one cable out of 15 that worked. I have adjustable supplies but since I have no schematics for this product I have no idea if I can just drop voltage on the .1 headers.

    User avatar
    LattePanda
    Site Admin
    Posts: 2555
    Joined: Wed Jan 20, 2016 9:09 am

    Mon Sep 05, 2016 4:39 am

    Boring wrote:Thanks for the tips. Do you have any suggestions on how to increase voltage if you Are using a lipo battery?
    if using a 7.5v lipo you could use in conjunction with something like this
    http://www.dfrobot.com/wiki/index.php?t ... U:DFR0205)
    it is then a case of adjusting a pot to your desired output voltage (obviously test voltage first with a meter to avoid any tragedies)

    hope this helps
    Enjoy Tinkering with LattePanda ! :lol:

    User avatar
    LattePanda
    Site Admin
    Posts: 2555
    Joined: Wed Jan 20, 2016 9:09 am

    Mon Sep 05, 2016 4:46 am

    KevinA wrote:Where did you find the CN2 reference? So far I have only found one web page with no detailed information,their DOC page. At the bottom of that page they list all the power supplies they have 'tested' with links, most of those supplies are for QC phones with triple power levels, 5,9,12 volt. I'm running a 12 volt 5 amp supply through a step down converter (not adjustable) that outputs 4 amp to a USB Host connector. I can use the USB cable off my QC Galaxy Note or I did find one cable out of 15 that worked. I have adjustable supplies but since I have no schematics for this product I have no idea if I can just drop voltage on the .1 headers.
    these supplies refer to delivering power via the micro usb
    afaik dropping voltage on the cn2 headers is not documented anywhere other than the forum, but i will push for this to be rectified
    if you have any suggestions please post on the content request board.
    Enjoy Tinkering with LattePanda ! :lol:

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