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### Topic: Arduino 5V pin (Read 1 time)previous topic - next topic

#### vick5821

##### Apr 12, 2012, 09:12 am
hey guys, when I measure the 5V pin, it does not givv me exactly 5V, instead I get 4.80 V..Is this normal ? What is the maximum sourcing current for the 5V pin ? How do I measure the currrent being sourced out by the 5V pin ?  just connect my Ammeter from the 5V pin to GND pin ?  when I do so, my  computer will give a feedback sound like when a USB device is plug in("de deng")..What is it actually ?

Thank you

#1
##### Apr 12, 2012, 04:07 pm
Quote
just connect my Ammeter from the 5V pin to GND pin

Don't do that. When in current mode you DMM is a very low value resistor, you're lucky you didn't blow something.

To measure current you have to insert the meter in series with the current or measure across a resistor that is in series. As there is no such resistor on an Arduino you would have to cut a track.

OTOH you could measure the current on VIN outside of the DC plug. Give or take a few uA that should be the same.

4.8v would not be normal, either the regulator is bust, VIN is too low, or you are drawing too much current.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

#### kf2qd

#2
##### Apr 12, 2012, 04:39 pm
If you are reading 4.8V when connected to the computer via the USB cable  you might be seeing a USB that won't quite supply the needed current so you are seeing a slight voltage drop. The Arduino will still run, but you probably don't have much current to run anything attached to the Arduino that pulls much current. The Arduino can run at 3.3 volts so it will continue to run but things connected might not work to well.

What else is connected to your Arduino when you make these measurements?

A Multimeter in Current (Amps, mA ) is basically a dead short. You insert it IN a circuit as part of the current path. In Voltage mode you measure ACROSS a circuit.

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