1. USB-C to HDMI bridge

This is the most crucial part of the project since it handles the video stream.

Currently, ANX7688 (and its related products) is a likely candidate due to its low power consumption and 4K support as well as being used quite frequently in USB-C to DP/HDMI dongles (even though HTC Vive supports only 1080p, it might support 90Hz+ refresh rate for smooth VR playback). However, this is only a preliminary search and things may change.

2. Power supply

Currently, there are four possible ways to do this.

  1. Convert from 12V to 5V on the Control Box side, increase it back to 12V on the headset side (adds SMPS noise, but is the safest option if there is more than one cable)
  2. Carry 12V through the VP and VN pin (VCC/GND) and use a Buck converter or linear regulator to drop it down to 5V to power peripherals (may waste a bit of power, and may blow up whatever is connected to the end if cables are mixed up)
  3. Use USB PD to request 12V, then use linear regulator for USB power and stuff (Might not play nice with USB 3.0/3.1 ports on PC)
  4. Don't do anything, just use external power (Easiest, but requires the adapter to be present)

3. Integration

HTC Vive requires at least 3 connections to operate -- 1 USB 2.0 connection (one port is unused and can be utilized for other peripherals such as eye trackers), 1 HDMI 1.4 connection at 90Hz or higher, and 12V 1A barrel jack input. The board's size needs to be within this dimension if it needs to fit inside the compartment (for seamless finish): 44.5 * 31.8 * 8.2 mm (excluding the "anti-mixup" slots)

One way to do this is to plug a short cable into the headset for each connection and use an external box to handle the processing (thus completely negating the need for the tight integration and tight tolerances)

Another way is to completely integrate the plugs into the design, meaning only one plug needs to come out of the headset (but I can see the challenges caused by the length of the USB-C connector, as there's not much room inside the compartment)

(Image source: UGREEN)

As you can see, there's not much room inside.