Wiring HDMI and Power into single USB-C cable for external monitor

[GertBreynolds]

I am starting a project to build a DIY monitor. I have a spare lcd panel (model # LP156WF6) taken out of a laptop. I plan on buying a controller board for it and building it into a homemade enclosure. The controller board has an HDMI input and a 12V/4A barrel connector for powering the display. I would like to wire both the HDMI port and the barrel connector into the same USB Type-C plug and use the same USB Type-C cable to power the monitor and send it its signal from the thunderbolt 3 port on my laptop (Dell Inspiron 7577 gaming). Is this even possible? I know HDMI over USB Type-C Alt mode has existed for a while now and allows you to send an HDMI signal natively over the USB-C, so I imagine buying a USB Type-C pinout PCB and soldering a split HDMI cable to it should be relatively simple using the attached wiring diagram I found on HDMI.org. For the power, is it possible to simply wire a small power regulation board in-between the barrel connector and the Type-C pinout? It seems there are many products out there that support power and signal through the same Type-C cable, so this seems possible, but I'm afraid I'm greatly oversimplifying the procedure. I would greatly appreciate any advice anyone out there may have on the subject.

[Chaftalie]

I can't say anything about signal quality, I do not know if HDMI will work after soldering it to an breakout board. Which resolution and refreshrate are you planning to use?

 

If I am interpreting it right, you want to power your monitor over the USB C Cable, which does not make a lot of sense, because your Laptop probably can't deliver that kind of power. (At least I never heard about a Laptop which can output Power with PD)    
EDIT (I just read somewhere that some/most Laptops can use their PD port to charge other things with PD):
powering your Monitor with your Laptop would need something like: https://www.tindie.com/products/oxplot/stusb4500-compact-breakout/
 

 

The other way around, charging your Laptop with your monitor makes more sense (at least for me) you would need a PD Module in the Monitor, which can negotiate with you Laptop how much power the laptop needs. There is a big Problem there, your laptop probably needs a powerbrick with more than 100W (max for USB-C, Dell has some USB-C power adapters with 130W, but with that they are stretching the USB-C spec a little.) so it won't charge with that solution. (I think your Laptop needs 180W)

 

EDIT2:

What I did not think through, is that in any way, you have to split your cable at your laptop to get the HDMI out.
What you could do to eliminate that, you can use a standard USB C to HDMI adapter t your Monitor and somehow get USB PD working over that

[GertBreynolds]

So the display is 1080p @ 60hz, which is supported by HDMI over USB-C alt mode. I guess the real question is if thunderbolt 3 supports HDMI over USB-c alt mode. I can't really find anywhere if it does, or does not support it. As for power, I'm trying to power the monitor from my thunderbolt port. I know the port will quick charge my phone, which is probably somewhere around 20w (I think its 9v 2a, but hard to know for sure). I think the board requires 12v/2a to run but again this isn't known for sure as it's not totally clear.

[Kilrah]

Alt mode isn't true HDMI/DP, it's a way to carry HDMI/DP data as packets over USB-C. It needs compatible controllers on both sides to do the bit shuffling. 

And you're not going to get 48W of power out of your TB3 port.

 

 

[GertBreynolds]

4 hours ago, Kilrah said:

Alt mode isn't true HDMI/DP, it's a way to carry HDMI/DP data as packets over USB-C. It needs compatible controllers on both sides to do the bit shuffling. 

And you're not going to get 48W of power out of your TB3 port.

 

 

There's no way it's using 48W. In DIY Perks youtube channel, he powers a very similar board using a 5v/3a battery bank with a usb-PD board in-between changing the supply voltage to 12V. I'd be surprised if the display uses more than 10W, well within the output range of a laptop's type-c port.

[Kilrah]

I have a 15" portable monitor that's powered through USB-C and must not be using much more than his, but if I go beyond 75% brightness or so when connected to my Dell laptop it cuts out.

Can go full on my desktop with no issue.

[GertBreynolds]

What I realize I need is some sort of adapter that is thunderbolt one one side, and HDMI and power on the other. These are common, but the usb-PD circuit is generally set up going the wrong way for what I want. Normally they're set up to charge your laptop while sending data to the HDMI, but what I want is to send HDMI out, and also the power out. I wonder if it's possible to take the adapter apart and change the Usb-PD circuit around so it's feeding power from the laptop to the monitor. Then I'd just need to put a chip like this one and set it to 12V in-between the monitor power and the adapter to tell the USB-PD to give power at 12V.