Question about arduino powering usb v. external

Development Tools IDE 1.x
1

I have a wifi-enabled arduino, connected by usb for programming.

I have an external power source (+5.02V) connected. When serial usb is connected, everything fine. When the usb is disconnected, I lose wifi - the led actually dims, so I checked voltages. When usb connected, all voltages are as you'd expect. When disconnecting usb, leaving +5.02V as main power, the voltage across the +5V pin reads 2.36V and the 3V3 pins reads 2.39V.

Can anyone shed light on this? I'm a software person - kinda stumped.

Another board exhibited the same behaviour.

Is there some jumper I need to set?

Many thanks.

brian...

2

What is your power source when not using USB? What is it and how is it connected?

3

When not using USB, I am using a 5V 1000mA power adaptor.

It is connected to the power in on the arduino board.

The board is an arsuino LinkSprite Diamondback - see http://www.linksprite.com/product/showproduct.php?id=74&lang=en

4

whatevernot:
It is connected to the power in on the arduino board.

Vin and Barrel Jack need 7V or more to operate stable. This is because they are connected to a 5V regulator. If you put 5volts into a 5volt regulator, you get less than 5volts out.

When not connected to USB, you should be connecting your 5volt supply directly to the 5V and GND pins of the Arduino.

5

Hi James - thanks.

I feel like a bit of a dolt when it comes to electronics - I dug up a 9V power supply, and that works when connected to the barrel jack.

Just want to clarify - when running without USB, I can connect +5V to the board directly? Would this connect to the 5V pin on the board, or to VIN?

Thanks.

b...

6

whatevernot:
t want to clarify - when running without USB, I can connect +5V to the board directly? Would this connect to the 5V pin on the board, or to VIN?

When not connected to USB, you should be connecting your 5volt supply directly to the 5V and GND pins of the Arduino. Do not connect 5 volts to Vin.