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 Forum index » DIY Hardware and Software » Arduino
external 5V supply + USB ?
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PHOBoS



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PostPosted: Sat Apr 06, 2019 4:41 am    Post subject: external 5V supply + USB ? Reply with quote  Mark this post and the followings unread

Is there a way to be able to use an external 5V supply but still have the option to plug in USB for programming ?
I could install a switch but that has the chance of forgetting it one day and maybe damaging the arduino or USB
port of my computer.

hmm, it looks like there is a schottky diode between the 5V from the USB and the rest of the arduino, so that
should already work, right ? (maybe with an extra diode between external 5V and arduino 5V input)

FYI: I am using an arduino nano (clone) to control some addressable LEDs.

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Blue Hell
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PostPosted: Sat Apr 06, 2019 8:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Two diodes should work .. like

Code:


 o---|>|---+
           +----o
 o---|>|---+



Is there no schematic? thought arduinos to be open sourced ...

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Grumble



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PostPosted: Sat Apr 06, 2019 8:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I do that, I have a dual 12volt euro connector and on the arduino nano an usb connector.
For programming I plug a usb power supply in the nano and program it with an icsp Dragon programmer. When the programming is done I use the euro connector, feeding the +12volt into the Vin of the arduino.
I do not use the arduino platform, but atmel studio with an added arduino functionality.

edit: you can also put 5volt to the Vin (sometimes called RAW input) and it will still work

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Last edited by Grumble on Sat Apr 06, 2019 8:45 am; edited 1 time in total
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Grumble



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PostPosted: Sat Apr 06, 2019 8:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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PHOBoS



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PostPosted: Sat Apr 06, 2019 8:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Two diodes should work .. like

Yes, that's what I was thinking since there is already a diode between the USB connector and the rest of the 5V on the arduino.
The 5V is the output of a voltage regulator but apparently it's not a problem to supply 5V to that, although I always add a diode
between it and the Vin just in case.

Quote:
Is there no schematic? thought arduinos to be open sourced ...

Schematics are easy to find which is how I know about the diode, I also measured it since I have a clone.
oh, grumble already posted one Very Happy

I think that with 12V you can just use the Vin, but I only have 5V.

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Grumble



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PostPosted: Sat Apr 06, 2019 11:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
 Speed Grade:
̶ 0-4MHz@1.8-5.5V,0-10MHz@2.7-5.5.V,0-20MHz@4.5-5.5V

The voltage/frequency dependancy is more or less linear, so if 10Mhz needs at least 2.7 volt and 20Mhz needs 4.5 volt, the atmega328 will run perfectly at 16Mhz @ 3.8 volt.
The power suply chip LM2940 used in the original Nano is a low dropout regulator with a dropout of about 0.5 volt, so when powered from 5 volt you are just fine!

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