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### Topic: Simple voltage input question (Read 938 times)previous topic - next topic

#### jeff77789

##### Mar 03, 2013, 05:50 amLast Edit: Mar 03, 2013, 08:12 pm by jeff77789 Reason: 1
me being new to arduino and all that....

I have an arduino Nano
i used a 5V regulator from a 9v battery to supply the power to VIN instead of +5V and i used the +5v pin to power something else

the +5v pin was actually giving me 4.6v

could anything have been damaged?

#### DVDdoug

#1
##### Mar 03, 2013, 07:33 am
Quote
That's  a little confusing...

5V into Vin won't hurt anything.   It's normal to get some voltage drop across a regulator.  In fact you need some voltage drop across the regulator in  order for it to work...  So, you need to put more than 5V into a 5V voltage regulator.

There is a spec is called "dropout voltage".   For example, if the dropout voltage for a regulator is 1 Volt you need to feed at least 6V into a 5V regulator or else it "drops-out" of regulation and no longer functions as a voltage regulator.

#### JimboZA

#2
##### Mar 03, 2013, 07:35 am
Quote
supply the power to VIN instead of GND

Not sure what you mean by "instead of"... You have to supply power to two connections anyway.... a single power connection is a bit zenny.

But that said, apart from 5VDC to the USB, any other power supply (ie to the barrel or to Vin) has to be between 6 and 20, with 7 to 12 recommended.

Edit... Hmmm, DVDdoug and I are in accord here.... confused by the "instead of"
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### retrolefty

#3
##### Mar 03, 2013, 07:50 am
The wording is awkward and not real clear, so it's hard to give advice. A drawing is what is needed even if it's handwritten, picture taken and posted. Just to be clear. applying +5vdc to the Vin pin is not a proper voltage, it's too low. Applying a regulated +5vdc to the 5V pin is OK.

Lefty

#### majenko

#4
##### Mar 03, 2013, 12:30 pm

Quote
supply the power to VIN instead of GND

Not sure what you mean by "instead of"... You have to supply power to two connections anyway.... a single power connection is a bit zenny.

Maybe he's passing it through a Zen diode?

#### JimboZA

#5
##### Mar 03, 2013, 12:34 pm

Quote
supply the power to VIN instead of GND

Not sure what you mean by "instead of"... You have to supply power to two connections anyway.... a single power connection is a bit zenny.

Maybe he's passing it through a Zen diode?

Ba-dum... Tsh....
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### majenko

#6
##### Mar 03, 2013, 12:51 pm

Quote
supply the power to VIN instead of GND

Not sure what you mean by "instead of"... You have to supply power to two connections anyway.... a single power connection is a bit zenny.

Maybe he's passing it through a Zen diode?

Ba-dum... Tsh....

Sorry, I couldn't help myself.  It was just going begging.

#### jeff77789

#7
##### Mar 03, 2013, 08:13 pm
my bad, sorry for all the confusion....

what i meant was that i supplied the power through the VIN pin but it was only 5 volts instead of the 6-20 volts that is suggested...

i took the 5v power from the 5v+ pin to power up something else so i used it as an output

hopefully that made sense

#### majenko

#8
##### Mar 03, 2013, 08:22 pm
Yes, that makes more sense.

If you put 5V into Vin (the same as the barrel jack on an UNO, etc) then you will get less than 5V out of the 5V pin, and the voltage regulator won't be doing its job.

You can put regulated 5V into the 5V pin and nothing in the Vin and it will be fine.

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