Wired network connection that does not mess up laptop's wifi

Hi guys, I have an unusual use case and I would like to know if what I want is even possible.

I am on a college rocket team. Our rocket has a Raspberry Pi in its lander. Per rocket contest requirements, the rocket is supposed to have a magnetic breakaway connector which I can use to tell the rocket’s data collection systems to start recording.

I implemented this by using a magnetic breakaway USB charging cable that supports data, and plugging that into a USB to ethernet adapter, which in turn connects to the Pi. I would have used USB to serial, but I needed to be able to copy pictures or even video off it.

I want to make the USB connection and control process as easy to use as practical, so I would like to give its local network the following features:

  • Configures IP addresses automatically
  • Does not interfere with laptop’s ability to use internet connection from another source (primarily for my own convenience while setting up the IT end of things)
  • Makes a captive portal that automatically directs the user to a web interface hosted on the Pi upon being plugged in

Here’s what I’ve accomplished so far:

  • Gave the Pi a static IP address
  • Set up a DHCP server on the Pi that issues an IP address to my Windows laptop successfully
  • Before I gave the Pi a static IP, I used Windows internet connection sharing to give the Pi internet access through my laptop’s Wi-Fi. I turned that off now, but I can re-enable it if necessary.

Here’s what I’m stuck on:

  • Make the Pi tell the laptop to keep using its existing default gateway
  • Implement a captive portal

Is what I want even possible? If so, how?

I am not sure if there is a captive portal in the software list of dietpi, so you’ll have to search in the list of the raspbian with apt.
For the laptop to keep it’s current default gw, you probably want to set the option 3 of the dhcp to NULL or

no we don’t have such software option.

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