I have a PING Ultrasonic Sensor, Adafruit Absolute Orientation Sensor, and a Continuous rotation servo. All pins are connected to an Arduino Micro. However because the micro only has one 5V output, I used a rail from a breadboard. I connected the + & - leads from all the devices to the rail and then plugged in two leads connecting 5V and GND from the Micro to the rail. My goal was two send power from the Arduino Micro down the rail to all three devices.
I plugged in the Micro, and instead of seeing green lights on the sensor (powered on), the blue light on the Micro turned off and the servo twitched. I have no idea why. Do I need external power for the 5V?