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Topic: Arduino voltage regulator feeding more voltage than input?! (Read 1 time) previous topic - next topic

SPimenta

Hello

I have an question that I cannot find the answer in Google:

I connect the USB (from computer) to the Arduino and when I measure the voltage with the multimeter the Vin pin (which is the voltage directly from USB computer) I read 5.19v and when I read the voltage from 5v pin (which is the voltage from arduino voltage regulator) and reads 5.6v !!!! And I measured the 3.3v pin and multimeter says 3.7v!!!

How can this be possible? More output voltage than input?

I've tried several computers with more voltage eg. 5.2v and the 5v pin feed even more voltage! Help me explain this!

Erdin

I know what it is. It is .......  impossible !

What kind of multimeter are you using ?
Which Arduino board are you using ?
Do you use the Ground from the GND pin ?

SPimenta

Its an Arduino UNO R1, and I'am using this multimeter: http://www.petervis.com/meters/Excel_DT9205A/Excel_DT9205A.html

I know thats impossible but is what I'am getting from the multimeter.

I connect the pins to an breadboard and I measure the Vin and 5V and 3.3V connected to the ground pin next to it on arduino.

I need to solve this to know the exact voltage to use the TMP36 to measure the temperature.

I also read the voltages directly from the voltage regulator and I'am getting the same thing!

Can this happen because I'am feeding only 5v? In arduino page says minimum 7v.

Erdin

Is that a cheap 10 dollar multimeter ?
They could easily be 10% inaccurate. Perhaps your multimeter has a problem and is even more inaccurate.
Most of those very cheap ones are only 1 or 2% inaccurate.

To be sure, you should use a better multimeter.

If you use the USB connector to power it, the voltage is perhaps a little below 5V. But that is not a problem.
The DC adapter plug is for 6...12V.
You could try an adapter. The Vin should be almost the same as the adapter DC plug, but the 5V should be 5.0V.
But you need a better multimeter to test it.

I suggest to use the USB to power the Arduino, and assume it is 5V, and use the TMP36 as you would (connect to 5V pin and GND and analog input).

retrolefty


Hello

I have an question that I cannot find the answer in Google:

I connect the USB (from computer) to the Arduino and when I measure the voltage with the multimeter the Vin pin (which is the voltage directly from USB computer)

No, The USB +5vdc does not connect directly to the Vin pin, study a Uno schematic. You are just reading some 'leakage' voltage on the Vin pin if your board is being powered only via it's USB cable.

I read 5.19v and when I read the voltage from 5v pin (which is the voltage from arduino voltage regulator) and reads 5.6v !!!!

The value of the USB's +5vdc is determined by your PC and can vary from 4.75 to 5.25 and still be within the USB standards. Your meter's calibration might be a factor in your reading of 5.6vdc, but who knows for sure?
And I measured the 3.3v pin and multimeter says 3.7v!!!

Again that might be a calibration error in your meter, but the value of the output 3.3vdc regulator is determined only by the regulator and will have some standard tolerance variation.

How can this be possible? More output voltage than input?

I've tried several computers with more voltage eg. 5.2v and the 5v pin feed even more voltage! Help me explain this!


Again the on-board +5vdc regulator is only powering the board if the board is being powered via it's external DC connector or it's Vin pin. If being powered from only the USB connection then the on-board regulator is not being used and is not supplying any current, nor is it determining the value of the Vcc bus for the board.

Lefty

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