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Raspberry Pi 7'' Touchscreen Display not powering on after energy failure

francisco.vaz

I have recently bough this display Raspberry Pi 7'' Touchscreen Display and got it to work just fine. The touchscreen works, the image looks great and i can control it with the Python module rpi-backlight.

 

However I stumbled upon a problem that haven't been able to solve so far.

 

I'm setting up a kiosk that contains this display, a raspberry pi, a 3g modem and a ups (uninterruptible power supply). The ups module is used to power the raspberry and the 3g modem so that on a power failure, the kiosk can perform some operations, send some data through the 3g connection and perform an orderly shutdown. In case of a short (in time) power failure, the UPS module is smart enough not to shutdown the system.

 

The problem that I'm facing is that on a power failure as the monitor is not connected to the UPS, it will shutdown but when the power returns the monitor will not turn on again. The screen stays blank as in no image, no power, no backlight. To make the monitor work again I have to turn of the UPS system, power off the raspberry, power the display, and then power it on all again. If someone has a monitor like this it can replicate this problem by simply powering the monitor off and on again keeping the raspberry on.

 

After spending some time trying to solve this problem I learned that this monitor can receive I2C commands, however I been unable so far to find out the command codes and/or how to send it a "power on" command if it even exists.

The Python module rpi-backligh as the functionality to turn the monitor on and off which works great at start, but won't do anything after the monitor shutting down due to a power failure.

 

My setup is:

Raspberry Pi 3 Model B v1.2

Raspberry Pi 7'' Touchscreen Display

RPI SIM800 GSM/GPRS ADD-ON V2.0

UPS PIco HV3.0 - Uninterruptible Power Supply & I2C Control HAT

 

For OS I'm running Ubuntu MATE 16.04.

The OS is fully updated (sudo apt-get update, sudo apt-get dist-upgrade) as the raspberry firmware (rpi-update).

 

Does anyone have any idea of how to overcome this problem? Or a list of the I2C commands that this monitor can receive?

  • 0

    The screen and Pi are normally powered from a single source. The Pi gets powered via the screen's USB output or via the GPIO, meaning you can't power on or off one without the other. See Raspberry Pi 7” Touchscreen Display .

     

    Is this different in your case?

  • 0 in reply to fvan

    I agree, powering separately is asking for trouble if you don't need to do that, since then you need to worry about switch-on order, and when any initialization occurs and maybe even applying a reset signal if such a thing is brought out to the connector.

  • 0 in reply to shabaz

    In my case both the display and raspberry are being powered by an external power supply (single source) that can provide enough power for all the devices I use. Even though the raspberry is not being powered by a cable originated from the display, the origin on the power is the same as the one to the display.
    As stated on my initial post, I have a UPS (uninterruptible power supply) connected to my raspberry meaning that independently of the raspberry power origin - being either the display or an external power source - on a power failure, the raspberry will keep running for some time but the display will not thus resulting on the display not powering on again without a complete system shutdown (display, raspberry, ups).

  • 0 in reply to francisco.vaz

    Could you explain with a diagram, because there is conflicting information.

    on a power failure as the monitor is not connected to the UPS, it will shutdown but when the power returns the monitor will not turn on again.

     

    ..

     

    can replicate this problem by simply powering the monitor off and on again keeping the raspberry on.

  • 0 in reply to francisco.vaz

    I'm guessing you're trying to describe some brownout scenario, but it is unclear. A diagram will speak a 1000 words.

    Anyway, if there is a brownout scenario, the issue lies with the UPS.

  • 0 in reply to shabaz

    The UPS that I use (UPS PIco HV3.0 - Uninterruptible Power Supply & I2C Control HAT) connects directly to the raspberry through the GPIO ports meaning that it will not power the display, only the raspberry.

    On the picture you can see (from left to right) the display, the raspberry, the ups module and the 3g modem. That blue "box" is the ups battery. On the back with a green led you can see the power supply that is being used to power all of this.

    image

  • 0 in reply to shabaz

    Yes, I am describing a brown out scenario where the ups keeps the raspberry powered for some time for it to perform some tasks before shutting down.

    However in the case of a short (in time) brown out if the UPS does not need to shutdown the system, the display will not work again.

  • 0 in reply to francisco.vaz

    Hi Francisco,

     

    I'm afraid you need an engineer to investigate, because there are misunderstandings here. When you say "it will not power the display, only the raspberry" I don't think that is what you mean, but it is unclear and I can't see where all the connections go in the photo. Whoever designed this for you can sketch a diagram, or diagnose this.

     

    I don't know if by a short time you mean a glitch, or some other time period before the software determines that a controlled shutdown is needed.

    Personally I would solve it with 'OR'd power supplies (one of them would be derived from a battery being trickle charged) but different engineers may implement things in different ways.

     

    You could also investigate a different vendor UPS, i.e. one that functions as it should and support brownouts. Bicker UPSIC-1205 might be interesting, I've not tried it, but it looks ideal. It has 12V output so you'd need a 5V DC-DC converter too.

  • 0 in reply to shabaz

    First of all thank your help and time image

    English is not my main language so I just realized that when i was saying brown out I actually meant a black out.

    On the picture, the red board is the ups, the blue battery is connected to it so there is no power going from it to the display, only to the raspberry and the 3g modem.

    When I say "it will not power the display, only the raspberry" what I mean is exactly that i.e. on a black out, the display will stop being powered but the raspberry will continue being powered by the UPS for some time. A short black out yes, could be a glitch on the power network, say a 5 seconds power failure. When this happens the monitor will shut down because is has no power, but the raspberry will continue being powered by the ups and as the ups realizes that the power is back, it will not perform the controlled shutdown because id deemed it unnecessary. On this case, the monitor will not display anything again until a full shutdown.

  • 0 in reply to shabaz

    From the comments and the picture, my guess is that things are connected as follows:

    image

     

    If that is correct, you could try the following:

    * remove the power input of the display

    * connect the display's power GPIO pins to the top HAT's power GPIO pins

     

    Assuming the UPS can handle the extra load, this will power the screen from the UPS' GPIO header, just like it powers the Pi and GSM HAT.