Hello i want to Run my arduino on a barrel jack but im not familiar with polarity did i connect those terminals correctly? btw i used a center positive one
it's right
but did i connect the plus and minus cables correctly?
Arduino barrel jacks are centre positive but if you are planning to use a PP3 battery to power your Arduino then I suggest that you think again
A PP3 battery cannot supply enough current to run an Arduino for long
As to whether you connected the barrel jack plug correctly, it is impossible to tell from your photo
Have you got a multimeter ?
If not then get one. A cheap one from Ebay is godd enough to meet your needs
You must test it with multimeter before connecting
And by the way, in your picture there is an adapter for a 9v battery - you should not use it, it has a very small capacity. Buy an external power supply DC 5v 1-2A and connect it to the 5v pin of arduino
i have a multimeter, why do you ask? i also have an orion 9v non cadmium and non mercury battery
since you are asking how to identify the correct wire in the cable. If you have a multimeter, it's not clear where this question comes from
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You have a multimeter, so use it to determine whether you have connected the barrel plug correctly
i will connect the multimeter minus probe to a ground connection then i will put the plus probe to the tip or the center of the barrel plug and see if it shows -8V or 8V
so that is how i check polarities and wish me luck and heres a photo
i did the connection correctly so thanks to everyone who tried to help me i am glad that you are here
and also a shoutout to @UKHeliBob
Convention is the multimeter Com(mon) is the black( -ve) wire !!! 
instead i put an led + leg to the tip then the lcd - to the ring jack
If you meant that you put an LED across the barrel jack connector then you should really have a resistor in series to limit the current
well mine worked without an resistor
How long will it keep working for?
the light emitting diode? around 1/2nd of an hour
I suspect you didn’t understand the question. I am asking how long it will continue to work without a resistor before it fails due to too much current. Obviously you are not going to leave it unattended when it is not protected from overcurrent by a resistor.
The arduino seems to be working fine without an resistor but when i apply a fresh 9v battery from duracell the lcd goes too fast, yes i have an stopwatch circuit
All the cheap wall outlets work “fine” up until they burst into flames. There is a reason why things are done correctly. If you want to wing it and see what happens that is fine but components have data sheets that give their maximum tolerances for a reason. Exceed them and they may still work “fine” up until they don’t. They are not guaranteed to fail safe
I meant to CHECK the polarities
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