I made a creeper farm in my survival world with the normal idea of trapdoors, carpet, a cat, etc. I know that the hopper system for picking up the drops will work, but no creepers will spawn in!
This is the tutorial I used if it helps any:Originally I built it just like he had it (which was relatively low to the ground), and nothing would spawn. So I raised it to be 128 blocks off the ground, because of the 128 spawn radius (which was really scary to build in survival lol).
I added torches on top of the farm so they wouldn't spawn there, and made a little room about 50 blocks under it to camp, and got nothing. After this I tried camping 50 blocks above the farm, and still got nothing. I built an antenna that went 20 blocks above the farm & 15 blocks out, still nothing.
To get the obvious questions out of the way, I am not on peaceful while I am camping. I am also the only player on my world. I am on windows 10 edition, I am not sure if that impacts anything. Also, it is definitely dark enough for mobs to spawn.