Hello, I just started using arduino a few days ago using USB that came with it. I was wondering if i could use this old adaptor that i found in my house to power the arduino but i have no experience in electronics whatsoever and i don't know if it is safe for my arduino.
INPUT: 220V 50Hz
POWER: 10W
OUTPUT: DC 9V
CURRENT: 850mA MAX
As you can see on the picture it has a switch to change polarity. If it is safe to use it what polarity should be switched to?
I saw a few simillar questions on forum but i couldn't fully understand the answers as someone that has 0 experience in that field and it was about different types of adaptors.
The plug must be 5.5mm OD with a 2.1mm center pin, the center pin MUST be POSITIVE (+). If you are not sure of polarity, don't plug it into your Arduino. Post a picture of the plug.
The Arduino Uno barrel jack needs + 7..9 V at the center pin and minus on the outside.
850 mA for the arduino alone is plenty. Thus, the power adaptor seems fine.
I understand your adaptor got a wrong plug. I'd hesitate to cut it off and apply the wires directly to Vin/GND pins, as the Arduino won't survive wrong polarity there.
Perhaps with a 1N4001 diode soldered between + and Vin...
That output is likely not regulated, so it might exceed what the Arduino can handle. You can check it with a voltmeter. I'm not sure what the max input on the barrel jack is...a quick flick of the googler says 12V?
Those power supplies, known as "wall warts", are typically unregulated. That is, the unloaded output is higher than what is stated on the label. It could be outputting 12V, or more. The device it was designed for very likely has its own voltage regulator. You could certainly measure its output with a voltmeter.
MK1888:
Those power supplies, known as "wall warts", are typically unregulated. That is, the unloaded output is higher than what is stated on the label. It could be outputting 12V, or more. The device it was designed for very likely has its own voltage regulator. You could certainly measure its output with a voltmeter.
I chceck direct current on my multimeter and it displayed slightly over 15V so i assume it is too much for the arduino right?
You'll have to see how hot the regulator gets. It doesn't go from 15V to 5V magically, it has to get rid of the difference...by heat. Your power supply says "850mA", so I would guess you'd be okay. But let us know if you let the magic smoke out.
A very real danger is that the obsolete tutorials on the Arduino site and others misleadingly imply that the largely ornamental "barrel jack" and "Vin" connections to the on-board regulator allow a usable source of 5 V power. This is absolutely not the case. It is essentially only for demonstration use of the bare board back in the very beginning of the Arduino project when "9V" transformer-rectifier-capacitor power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.
If you are asking this question, it is highly likely that you will wish to connect something else. In which case, the answer is regulated 5 V.
This is because the on-board regulator is essentially capable of powering only the microcontroller itself and no more than a couple of indicator LEDs. The on-board regulator might be able to power a few other things if it had a heatsink, but on the (older) Arduinos, it does not.
Powering via the "barrel jack" or "Vin" connections is asking for trouble. The "5V" pin is not by any means an output pin, if anything a "reference" pin but most certainly the preferred pin to which to supply a regulated 5 V.
