Assuming you're using the CLI tools (since the machine should be up all or most of the time), you should start the daemon process monerod
with the --rpc-bind-ip
option, and then the IP address of the machine, e.g.:
$ monerod --rpc-bind-ip 192.168.0.100 --detach
Then any other device on the same 192.168.0.*
network will be able to point to your internal node, e.g.:
$ monero-wallet-cli --daemon-host 192.168.0.100 --wallet-file ...
If you're not using the CLI tools, but the Monero Wallet GUI instead, you can still pass that --rpc-bind-flagip
option on the Settings page in the "Daemon startup flags" field. Equally, from other machines, you can point to the remote node in the "Daemon address" field (also on the same Settings page).