The closest I ever got to a data sheet was assembler coding for an 8080 and a GE425. Mostly I used Fortran and Cobol until C came along. I did look at the Atmel data sheet, but the I2C section was something like 7 pages - I'm a software type :-). Could be. So I took a completely bare Nano and hooked it up to the servo controller using only 5V,GND, SDA, and SCL as per the diagram in the AdaFruit instructions. Then hooked up a separate 6V supply to the controller to power the servos.. And yes, the I2C sniffer found the controller. But running the AdaFruit test program no servo movement occurred. SO: I tested the servo power plug to make sure it was indeed 6V. But testing the connection point on the controller, with both boards powered up, I was getting only some fractional voltage. No wonder the servos weren't moving :-). So just on a whim, I removed the power (USB) from the Nano. Lo and behold I now had the full 6V on the controller. There is absolutely no connection between the 6V servo supply and the 5V and I2C on the Nano. Unless it's all the way back at the wall sockets. Gremlins flourish! I'm going to try again with a wall wart instead of USB power, and then with a Uno instead of the Nano. Is it possible that the I2C pins on the Nano are somehow being treated as analog inputs?