using external HDMI display with balena-dash (& 7" touch screen)

just completed the balena-dash project, and currently displaying a slide show based on photos stored on Google Photos. I thought it would be cool to simultaneously have the same slide show photos appear on the living room TV. I connected the Pi 3B+ to the TV using a HDMI cable. No picture, no signal. What do I need to do to mirror what is being displayed on the 7" touch screen, to the HDMI interface ?

Hey @AZbman welcome to the forums!

This isn’t something we support within the project and from what I can find this isn’t a simple thing to do on a Pi 3B+ either. I had a quick look to see if I could see any quick answer for you but didn’t come up with anything see here:

It looks like it might be possible if you were using a Pi 4, see here, but it probably won’t work straight out of the box:

kindest regards