Configure RP with HA to two networks for portability

I’m just getting started on a university project requiring me to take my setup in for a demonstration. Because of this, I’m trying to configure my home assistant on a separate network from my home network. So I have a router with my pie directly plugged into it. This is then connected to various Arduinos on the same network. However, I want to connect my HA to a webserver through websockets to talk to an external application that controls various automation. This would require me to connect the HA to the internet. For this, I’m planning to personal hotspot my phone. The problem I need to work out is how can I connect my HA to my personal hotspot so it can then have an internal connection talking to my external server and still have it connected to its network of Arduinos.