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Author Topic: Tapping power off the DC jack of Uno  (Read 929 times)
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I want to mount my Uno in a nice Aluminum enclosure, with the DC jack and USB port sticking through the rear panel.  I will power it with a 12VDC wall wart.
My question is, I'm needing 12VDC on some other circuitry inside my enclosure (to run a sollenoid), so is there any reason why I can't carefully solder a wire to to back of the DC Jack on the Uno, to tap off the 12V coming in?  (There's no real place on the board to get this power, is there?)
thanks
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I see no reason why not, as long as the power supply provides enough current for all connected systems.

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I want to mount my Uno in a nice Aluminum enclosure, with the DC jack and USB port sticking through the rear panel.  I will power it with a 12VDC wall wart.
My question is, I'm needing 12VDC on some other circuitry inside my enclosure (to run a sollenoid), so is there any reason why I can't carefully solder a wire to to back of the DC Jack on the Uno, to tap off the 12V coming in?  (There's no real place on the board to get this power, is there?)thanks

Yes there is a place. When the board is being powered by the external power connector, that voltage is then available on the Vin pin of the arduino power shield connector to be used for external components rated to use that voltage, +12vdc in your case.

However the first thing you have to determine is what the current demand for your solenoid is? There is a series polarity protection diode between the external power connectors positive terminal and the Vin pin and it probably has a 1 amp maximum current rating. Your external power module also has to have a maximum current rating sufficient to power the arduino board and all other external components being powered.

Lefty
« Last Edit: February 08, 2011, 11:36:12 am by retrolefty » Logged

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I want to mount my Uno in a nice Aluminum enclosure, with the DC jack and USB port sticking through the rear panel.  I will power it with a 12VDC wall wart.
My question is, I'm needing 12VDC on some other circuitry inside my enclosure (to run a sollenoid), so is there any reason why I can't carefully solder a wire to to back of the DC Jack on the Uno, to tap off the 12V coming in?  (There's no real place on the board to get this power, is there?)thanks

Yes there is a place. When the board is being powered by the external power connector, that voltage is then available on the Vin pin of the arduino power shield connector to be used for external components rated to use that voltage, +12vdc in your case.

However the first thing you have to determine is what the current demand for your solenoid is? There is a series polarity protection diode between the external power connectors positive terminal and the Vin pin and it probably has a 1 amp maximum current rating. Your external power module also has to have a maximum current rating sufficient to power the arduino board and all other external components being powered.

Lefty

GREAT!  I was wondering about that Vin Pin...  My solenoid is 575 mA. So I'll be fine up to 1 AMP, then...  I want to see if I can find something on this Vin Pin in the datasheet.
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Sure enough, here it is:
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VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
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mount my Uno in a nice Aluminum enclosure
IIRC - Aluminium is a conductor .... and I wondered how you do the isolation. But that said, it could be used as a generic GND for both 5V and 12V I guess...
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Why not put a panel mount jack on the sidewall and break off the DC to your 2 locations from there?
Ok, I reread - you want the connectors to be accessible so you plug in direcytly.
I would go with soldering to the bottom of the board at the jack itself then, the metal the jack pin will keep all that current from having to go thru the board traces as well.
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...Ok, I reread - you want the connectors to be accessible so you plug in direcytly.
I would go with soldering to the bottom of the board at the jack itself then, the metal the jack pin will keep all that current from having to go thru the board traces as well.
Good idea, I think I'll do the careful soldering.  ...about the anodized aluminum box-enclosure- it doesn't matter that it will touch the USB casing.  ...and the DC jack is plastic, so it won't be touching...
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