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Hello Arduino Community!

I've found a nice 5v ac/dc power adapter which i want to use to power up my arduino. now the thing is when i measure V instead of 5 i get 8.~ which may be okay i guess. what bothers me however is that symbol on the output side:

__
---

(that is a line and three dashed lines below, instead of two parallel lines = )

I wonder if that means that the output is somehow on the principle of the PWM and i need a condensator to make use of the adapter? If yes, how do i dimention it?

TIA from a newbie

VAlerio
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Regards,

Valerio

Dubuque, Iowa, USA
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I assume it shows something like "5V == 1A". The dashy symbol thing is just a symbol for DC current.

Don't overthink it smiley-wink
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okay got it smiley-wink
thanks!
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Valerio

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I assume it shows something like "5V == 1A". The dashy symbol thing is just a symbol for DC current.

No, its the symbol for a DC voltage...
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I've found a nice 5v ac/dc power adapter which i want to use to power up my arduino. now the thing is when i measure V instead of 5 i get 8.~ which may be okay i guess. what bothers me however is that symbol on the output side:

As others have said, that's just the symbol for "DC power"

What bothers me is that is says 5V but you measured 8V. That means the supply is unregulated. It's designed to drop down to approximately 5V when you apply a certain amount of load to it (and we don't know what that load is...)

If you connect it to the Arduino external power socket it might drop down too low for the voltage regulator to work and the Arduino won't get a full 5V.

If you connect it directly to the Arduino 5V pin it might supply more than 5V and hurt the Arduino.

In other words: It's bad news. I wouldn't use it with an Arduino if I were you.
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hahaha, okay thanks for that. not sure i grasp exactly what you mean (in particular how would the thing stop at 5v and not drop further?).

BTW i thought that the symbol for dc was the two parallel lines =
while i never heard of one dashed and one full line
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Valerio

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hahaha, okay thanks for that. not sure i grasp exactly what you mean (in particular how would the thing stop at 5v and not drop further?).

5V is approximate and only when it's connected to the device it was designed for.

It will drop further than 5V under heavier loads.
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Switchmode regulators that hold the output at 5V and are internally protected against external short circuits are commonly available.  I would not consider using anything else these days.
5V for regulator-less designs
http://www.dipmicro.com/store/DCA-0510  1A
http://www.dipmicro.com/store/DCA-0520  2A
http://www.mpja.com/5-Volt-DC-Plug-Power-Supply-4A-Regulated/productinfo/18520%20PS/ 4A
More here too
http://www.pololu.com/category/84/regulators-and-power-supplies

board connector
http://www.dipmicro.com/store/KLDX-0202-A

panel mount connector
http://www.mpja.com/55mm-OD21mm-ID-Chassis-Power-Connector/productinfo/18549%20PL/

barrel to screw terminal adapter
http://www.mpja.com/55_21mm-Power-Jack-Screw-Terminals/productinfo/19454%20PL/

Dual splitter cable
http://www.mpja.com/DC-Power-Splitter-Cable-30cm-Dual-Male/productinfo/19450%20CB/

Quad splitter cable
http://www.mpja.com/DC-Power-Splitter-Cable-40cm-Quad-Male/productinfo/19451%20CB/

7.5V for feeding into barrel jack connector on Arduinos
http://www.dipmicro.com/store/DCA-07510

9V, 12v when strings of LEDs are involved
http://www.dipmicro.com/store/DCA-0910
http://www.dipmicro.com/store/DCA-1210

I've used all of these (except the splitter cables) and keep a couple of each of them on hand for projects.
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The dashy symbol thing is just a symbol for DC current.
No, its the symbol for a DC voltage...
As others have said, that's just the symbol for "DC power"

Oooh!  Oooh!  No one's taken DC resistance yet, so that one's mine!   smiley-lol

OP:  Does the adapter have a current rating on it?  (5V @ 100mA or something like that.)  As others have said, with unregulated supplies, the unloaded voltage is higher, and as load is applied, the voltage drops more and more.  At a short circuit, it would be 0V.  (Until it broke.  Well, then it would still be 0V, and would also smell funny.)

The trick with these is to have enough capacity that the load you'll place on it does not bring it below the minimum voltage at which your device can run.  If that power adapter can't supply at least 500mA, I wouldn't bother with it for general use.  (Some projects can function very well with 100mA or less of supply capacity, but until you know, you should have some wiggle room.)

At 8V, you're not going to damage the barrel jack input on your Arduino, so go ahead and try it.  After you have it plugged in, and your project is running, measure the voltage on the Vin pin (which is basically straight from the barrel jack), and also the 5V pin.  Make sure the 5V pin measures between 4.5V and just over 5V.  Ideally, Vin should be 6.5V or higher.  (Higher is good up to about 12V -- which your adapter won't supply, but another might.  After 12V, the onboard regulator has to drop a lot of voltage, and will heat up considerably doing so.  Not good practice.)

People seem to loathe the idea of running a regulator in that region below its minimum input voltage, but AFAIK, there's no harm in doing so, it just won't be able to regulate the voltage to 5V.  So what?  The IC doesn't need the input voltage to be 5.00V on-the-dot, nor does it really need to stay within 1% +/- while it's running.  Significant (and especially transient) fluctuation isn't good, but hopefully the supply and decoupling caps prevent that anyway.  Am I wrong here?
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okay i understand, i guess it's normal though that when you put a load -the arduino in oru case- there will be a drop in voltage.
or should have i payed more attention during my physics class? smiley
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Valerio

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For an unregulated supply, that's just how it works.  Regulated supplies adjust internal resistance, current draw, and/or duty cycle to counteract the load.
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