Mega 2560 R3 Voltage

[bmoseley]

I have a new, genuine, Mega 2560 R3 board. Having dealt, primarily, with Hybrid Vehicles, for the past 18 years I have become a "one step at a time" guy. I was checking the voltages out on this board. With the board bare and connected by a USB cable I am getting 5 V out on all 5V pins and 3.3 V out on the 3.3 V pins. However, when connected to an external regulated, 5v power supply, I am getting 3.3 Volts on the 3.3 v pins and 3.3 v on the 5V pins.

I confirmed that there is 5.1 volts at the back of the female barrel connector.

Bad Board?

Any help would be greatly appreciated.

Thanks in advance.
Bill

[missdrew]

Minimum 7V to the Barrel connector, it has an inline protection diode.

[bmoseley]

Would the protection diode be M7? If so, that would explain it. I have 5.1 v into M7 and 4.4v coming out.

I am new at Arduino. I may be adding a servo shield and 6 rc servos. I will be picking up servo motor operating voltage directly from the power supply. If so, what power supply would you recommend. . Volts and amps.

Thanks

[slipstick]

The point is that connector is specified for 7V minimum and runs through a regulator to generate the 5V.

Servo power supply required depends on what the servos are. Servos may run on 5V, 6V or more and may need less than 1A or more than 5A each.

Steve