Switching between HDMI0 and HDMI1 for portable build

tusabez

Hi everyone,
I'm building a portable briefcase unit with a raspberry pi 4 and laptop screen connected to an lcd controller board. I have Retropie running fine using HDMI0 connected to the controller board. On HDMI1, I've connected a second cable to be used as an HDMI out when plugging to a TV when I want a bigger screen. The trouble I'm running into is that even though I have a separate power button for the controller board, when it's off, I can't get signal sent to HDMI1. The only way this works is if I physically unplug the cable from HDMI0 so that it forces the pi to use HDMI1. It's a bit of a hassle as I have to pop off the joystick and buttons panel in order to access the pi and unplug the cable from HDMI0. Any ideas on how I can make this work? Thanks

YFZdude

@tusabez
Most devices can detect whether an HDMI cable is physically plugged in or not and this is likely what is causing your headache. There is an "electronic load" on the line even if the controller board is in the off position.

My first thought would be a plug that has a physical disconnect switch on it but I didn't see an easy answer for that. The other idea would be if you could incorporate a "HDMI switch" and only use the HDMI 0 plug on the Pi to go to it. Then select which output you want to use.

Of course this only works if you can incorporate it into your build.
https://www.amazon.com/Monoprice-108150-Switch-Optional-Output/dp/B0097K49VK

EDIT: A splitter may be the solution instead of a switch. I forgot inputs vs. outputs.
https://www.amazon.com/1JUSTLINK-Switcher-Splitter-output-Support/dp/B0197PPSA0

EDIT 2:
https://www.amazon.com/NewBEP-Splitter-Amplifier-Switcher-Support/dp/B01MT12OQA

The only disadvantage is that a splitter may cause the resolution to be forced to 1920x1080 or something similar which may not match your laptop screen.

tusabez

@yfzdude cool thanks for the suggestions. I was looking at an hdmi splitter too but it's pretty tight with space in the case.

ExarKunIv

@tusabez not sure if this way would work for you, but you could find the pin out for a HDMI cable, and put a switch in line of 5v or the CEC.

since room is kinda a problem for you and this way there is nothing else drawing power as a HDMI switch needs power i believe

tusabez

@exarkuniv Ok now I feel extremely stupid for not thinking about this before. But because I'm probably not the only one, I figured I'd post this info in case others run into the same thing. After wasting more than half a day trying different HDMI configurations and editing the config file a million times, I realized that by plugging in HDMI 1 into the lcd controller and using HDMI 0 as the output source for a bigger TV, the pi will always check HDMI 0 first for signal and if it doesn't find one, then it goes to HDMI 1. So in other words, no need for an HDMI switch or splitter. Man I feel so stupid but at least the problem is solved now.