Simple Arduino Uno Voltage Question (5V?)

Hi all,

I'm very new to arduino and know very little about electronics in general so please bear with me :slight_smile:

I have an ardunio uno (version 1) I believe and I was learning how to make a temperature sensor. Everything worked fine although I was getting some readings that were too high. I disconnected everything from the ardunio and got out my multimeter and measured the voltage between the 5V pin and GND and got a reading of between 4.94 and 4.96V. I want to use the ethernet shield with my sensor and when I have that connected I get a reading of 4.57V. This is with the ardunio powered by USB from my mac.

Obviously, this affects the reported temperature reading. The 3.3V pin gives a 3.3V reading constantly.

If I then power the arduino using an iPod charger via USB I get 5.05V and 4.71V with the ethernet shield.

Is this normal? Should the arduino not have a constant 5V?

Am I missing something and being stupid?

Please help.

Matt

4.57V really sounds like you're dragging Vin down by overloading your power supplies
What are the Vin values in these circumstances, ie, Power header, 'input' side of
the voltage regulator?

Try powering the board from a good wallwart, rated 9V at 500-mA or so, and see what happens.

There is nothing attached to the arduino except the USB cable and an ethernet shield

Check what the +5vdc current requirement specification is for the Ethernet shield. I suspect it may be higher then the 500ma limit when using +5vdc via the USB connector. You can gain some more +5vdc current capacity by powering the board with a 1amp 7-12vdc external wall wart type power module that plugs into the arduino’s external power connector.

Lefty

There is nothing attached to the arduino except the USB cable and an ethernet shield

Just the same, what is the voltage at the input to the voltage regulator when you are
measuring 4.57V on the buss?

oric_dan(333):

There is nothing attached to the arduino except the USB cable and an ethernet shield

Just the same, what is the voltage at the input to the voltage regulator when you are
measuring 4.57V on the buss?

He said he was powering the Uno via the USB, so the on-board voltage regulator would have 0 volts on it's input. The on-board +5vdc regulator is only in service if there is voltage applied to the external power connector or the Vin pin, of the proper 7-12vdc range.

Lefty

He said he was powering the Uno via the USB, so the on-board voltage regulator would have 0 volts on it's input. The on-board +5vdc regulator is only in service if there is voltage applied to the external power connector or the Vin pin, of the proper 7-12vdc range.

Ah so, then I'd try a wallwart, as we both mentioned.