I ordered a 7 inch hdmi touchscreen for the Raspberry Pi 3 on ebay and started developing my Python openCV application.

So my setup is a Raspberry Pi 3 + webcam + 7 inch touchscreen powered via usb

During development I noticed a lightning bolt icon in the upper right corner. It is a undervoltage warning, so I ordered a 3A power adapter. But this didn't help.

I also noticed my webcam video framerate performance was horrible, but as soon is I powered the touchscreen with a 2nd power adapter instead of via the Pi all my speed and power problems disappeared. The downside is that I don't have any touch input now.

The original setup with touchscreen powered via the Pi draws around 1.1Amps The touchscreen itself draws around 0.9amps

This is measured with a usb power meter, but I'm hesitated if the results are correct, because this will mean Raspberry + webcam is only 0.2amps with running opencv application with 55% CPU.

Are the 4 USB on the raspberry limited to a certain amount of milliamps?

Update: In my /boot/config.txt my max_usb_current is already default set on 1

  • Maybe someone else will explain better, but I think you can connect both an adapter and the Pi to the screen? So, I mean, have two adapters, plus the USB connection. – Tomas By Jun 29 '18 at 15:58
  • Well the touchscreen X and Y position is send over the same usb, that is why I'm missing touch input as soon as I use two adapters – user3411864 Jun 29 '18 at 16:00
  • I thought you disconnected the Pi from the screen to connect the adapter? – Tomas By Jun 29 '18 at 16:01
  • Exactly, so then your touchscreen gets power via an external power adapter, but your touch input X and Y coordinates has to send to the raspberry. – user3411864 Jun 29 '18 at 16:03
  • 1
    Yes, and then the Pi will have a total limit also. You should try to use two adapters I think. – Tomas By Jun 29 '18 at 16:09

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