Want to stay somewhere half way one night...at campground

Hartford is roughly halfway between Pittsburgh and Bar Harbor so you could look for somewhere in that area.
If you put 'campground connecticut' into https://google.com then click 'Maps' you'll see several campgrounds which are both in the Hartford area and fairly near the I-84 (you'll leave the I-84 just north of Sturbridge). 
E.g. South of Hartford:
Lake Compounce Campground just south of Plainville https://www.lakecompounce.com/campground
Northeast of Hartford
Wilderness Lake Campground near Stafford Springs (Connecticut) https://wildernesslakect.com/
Moosemeadow Camping Resort   https://moosemeadow.com/ and Brialee Family Campground https://www.brialee.com/ both near Willington

There are, of course, other CT campgrounds which are further away from the I-84.