Want to install two WordPress but with same dashboard

I have a site (assume https://mysite.com) where I do some experiments.

I want to install WordPress on my website but I want different ones; one for the technical (analysis on the experiments I did, how did I made them etc.) and another one for non technical blogging (something like:Google Chrome 20 released, with dual mouse support).

But when installed two dashboard the main problem I will face will be updation of themes, it will be hard to update bot wordpress one by one.

What can I do in this situation?