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Topic: Uno External 5V direct connect? (Read 767 times) previous topic - next topic

louarnold

I have a Rev3 Uno. Is there a way of using a 5V external supply (from a 7805 regulator) to power the board?
I mean without modifying the board?

retrolefty


I have a Rev3 Uno. Is there a way of using a 5V external supply (from a 7805 regulator) to power the board?
I mean without modifying the board?


Well the way I do it is to get an old spare USB cable and lop off the PC end, separate out the ground and +5vdc wires and wire them to your external +5vdc voltage source. Then just plug it into the arduino's USB connector.


Lefty

strykeroz

Alternatively you can bring the +5V into the headers directly, as that bypasses the onboard regulator too.  You could do that with a simple pair of male headers connecting to +5V and the adjacent GND, or put those on a small perfboard as a shield if you want to use a screw terminal or similar to secure your external power line.

Geoff
"There is no problem so bad you can't make it worse"
- retired astronaut Chris Hadfield

louarnold



I have a Rev3 Uno. Is there a way of using a 5V external supply (from a 7805 regulator) to power the board?
I mean without modifying the board?


Well the way I do it is to get an old spare USB cable and lop off the PC end, separate out the ground and +5vdc wires and wire them to your external +5vdc voltage source. Then just plug it into the arduino's USB connector.


Lefty


Hahaha, of course...an easy solution. And then I would be sure to disconnect that USB cable with the one from the desktop when I want to program the micro. When programming the micro, would that create a problem between the 5V on the USB cable running the Uno, and the external regulator feeding other components.

louarnold


Alternatively you can bring the +5V into the headers directly, as that bypasses the onboard regulator too.  You could do that with a simple pair of male headers connecting to +5V and the adjacent GND, or put those on a small perfboard as a shield if you want to use a screw terminal or similar to secure your external power line.

Geoff
Yes, I though of that, but then I would need to be sure to remove that 5V wire when I plug in the USB cable to program the micro. That seems a risky approach.

dhenry

Quote
from a 7805 regulator


The only regulator that pukes being reverse charged, in my experience, is 1117: they get very hot quickly.

Never had a problem with 780x.

CrossRoads

NCP1117 is what's on Uno R3.
http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF
Page 10 would suggest a diode from +5V to Vin might be a good idea to keep from damaging it.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

retrolefty




I have a Rev3 Uno. Is there a way of using a 5V external supply (from a 7805 regulator) to power the board?
I mean without modifying the board?


Well the way I do it is to get an old spare USB cable and lop off the PC end, separate out the ground and +5vdc wires and wire them to your external +5vdc voltage source. Then just plug it into the arduino's USB connector.


Lefty


Hahaha, of course...an easy solution. And then I would be sure to disconnect that USB cable with the one from the desktop when I want to program the micro. When programming the micro, would that create a problem between the 5V on the USB cable running the Uno, and the external regulator feeding other components.


There can always be a problem with you have an arduino powered off and external wired components or modules powered on but still wired to the arduino. This can cause current to flow through the I/O pin's clamping diode and attempt to power up the arduino through an I/O pin and risk damage. This can be dealt with by using diode or series resistor to limit such current flow but the details of course depend on the specific things you have wired to the arduino.

Lefty



retrolefty

#8
Dec 20, 2012, 02:11 am Last Edit: Dec 20, 2012, 02:14 am by retrolefty Reason: 1

NCP1117 is what's on Uno R3.
http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF
Page 10 would suggest a diode from +5V to Vin might be a good idea to keep from damaging it.


Agreed, perhaps the Uno Rev4 will add another diode to the board, much like they did for Rev3 design for the auto-reset latch up problem. Sooner or later they will chase all the gremlins from the Uno.  :D

If you recall from past years my favorite method of selecting +5vdc voltage source on a arduino board is using jumper clips like they used on the very first arduino designs and as you have used on several of your board designs. KISS is a powerful tool.  ;)

Lefty

CrossRoads

Not if they keep introducing new ones like changing the regulator did.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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