I am not 100% sure this question relevant here , but question is I have lv maxsonar ez which need 5v. I am powering my uno with 9v battery. And I have few other sensors also connected to 3.3v. But I have neopixel 3 meter LED which is powering with external power source which is 5v 4 amp. So My question is shall I connect my sonar sensor to the external power or keep with my uno 5v power ?