I have the following 7inch HDMI LCD display: Image of 7inch WaveShare 1024x600 Touch Screen LCD

As you can see it has an HDMI and a micro usb connector. So far for pure rendering I have connected HDMI to my R-PI and micro USB via an adapter to 5V/GND external power. Like this the R-PI never went into under voltage because it did not have to give roughly 0.5A to the LCD.

Problem: Touch screen works only via the micro usb adapter, when connected to the USB port of the R-PI. This means that I am now taking the 0.5A from the R-PI instead of the external power supply. This regularly causes short periods of under voltage on my PI-4.

Idea: Use a micro USB breakout at the LCD, a regular USB breakout at the R-PI. Connect TX and RX and FWIW also 3.3V accordingly, but take 5V (and maybe GND) of the LCD breakout from the external PSU and leave them unconnected at the R-PI (at least 5V).

Note: R-PI is also powered via the same external PSU, so they are referencing the same ground.

Is this feasible? Are there better options?

  • Feasible as far as I can tell so far: Yes. Took a micro USB to USB-A female converter, took two blank USB-A male heads and soldered D+ and D- together and on one of them soldered two cables on GND and 5V going to an external power supply. That header plugged into the female part of the LCD (micro -> A female), the one with only D+ and D- to the R-PI USB input. Touchscreen is still there and since there is no connection except D+ and D- with the R-PI no power flows between R-PI and LCD which is fully powered by external PSU. Still waiting for someone to tell me if thats a good idea though :) – Yanick Salzmann Oct 26 '20 at 20:19

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