Whats the easiest way to gain muscle without spending money?

I've been taking a multivitamin and increased my protein intake, but i want to gain muscle without spending money buying weights or going to the gym. I don't want to be jacked or anything, just a decent amount of muscle. I'm 5'10 135 lbs. All I have around there is around the house is like 5 and 10 pound weights, although I believe I've heard that there are some strenuous exercises with those(don't know if thats true)