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[on:]

The past couple days I've been working to have Arduino Uno replace another board that I had on a robot. I've done all the work I can through the USB connection and it works fine, but now I want the robot to follow the wall on the floor. It'd be nice if I didn't have the USB cord in the way.

So I've done my research and I'm ready to connect the Arduino to an external power source. The battery is giving off around 8.3V, I've read that the Arduino can take 7-12V, however, when I plug in the battery's power jack to start the board, nothing happens.

The board still works fine through the USB, and nothing has really given me a reason to think I fried the board. I just wanted to confirm that what I am doing is correct before I try again. I'd rather not fry the board.

[Reply #1 on:]

As I sit here typing this, that's exactly what I have running in front of me....

A 9v nominal, 8.3V actual (how's that for coincidence?) PP3 plugged into the Uno barrel plug. The servo gets its own power from 4x AAs and the grounds are coupled.

All working as expected.

You sure you have the battery polarity the right way round- centre positive.

[Reply #2 on:]

So I've done my research and I'm ready to connect the Arduino to an external power source. The battery is giving off around 8.3V, I've read that the Arduino can take 7-12V, however, when I plug in the battery's power jack to start the board, nothing happens.

Yes, that is all I can think of, polarity of your 8.3vdc power plug is wrong for an arduino? Must be center pin positive and if reversed there is a polarity protection series diode to prevent damage to the arduino board, but would give you the symptom you see, nothing works and the board's power led would be off.

Lefty

[Reply #3 on:]

Jimbo, thanks, you were right.

I just ran off to get some firsthand help. The robot was meant for first year engineering students and the person who designed the robot before didn't want the students to have to worry about polarity yet. The polarity is the wrong way around for Arduino. Going to make a new power jack and try again.

[Reply #4 on:]

Jimbo, thanks

Don't thank me, thank the Arduino guys who put that anti-fry diode in the Uno 

[Reply #5 on:]

Made a new jack with the polarities reversed. Sure enough, it works fine now.

Thanks, guys! And thank you Arduino dudes for those diodes. I may have had a breakdown if I fried the board.