I was hooking up my Arduino Uno today to a 9V power supply (220AC to 9DC), and unfortunately I had fed the negative terminal to Vin on the arduino, and the positive terminal to the GND PIN.
Very quickly I saw the LDO (at least what I beleive to be the LDO) heat up, smoke, and then die down again. I imagine I have friend that component.
Oddly enough, when correcting my error and reversing the pins, my board continues to function and my programs still work. This brings me to wonder what exactly the LDO does, and if it will be safe for other components in my project if I continue to use the same board. Does anyone have the answer to these two questions?
You're right, I am mistaken. It does continue to work as long as I am using a USB power source, but power from my power supply no longer does the trick. This appears to have been an expensive mistake.
Before I buy and plug in another arduino, can I expect it not to fry if I have my issue with the positive and negative leads sorted? They are about 60 dollars here, so I am hesitant to plug another one in.
byteofthat:
can I expect it not to fry if I have my issue with the positive and negative leads sorted?
Sure, if you don't do that again then that shouldn't happen again, for that reason.
How did you manage to mess it up?
What's the plan for Corrective Action, Mistake-Proofing?
Provided you get that right, and you don't exceed Vmax_in, or do anything (else) bizarre / harmful, then you should be OK.
I messed it up by nothing other than making assumptions. I should have checked to make sure that I understood for sure if the power supply I was playing with had a negative or positive center. I have a Jack that it's plugged into and I run wires from it to the Vin and ground. Corrective action and error proofing will be using my voltmeter to make sure I understand which wire is which.
Thanks for the help!
Though lastly, I must admit that I am surprised there isn't a different in there to prevent an idiot like me from making this mistake. Any intentional reason one isn't there?
byteofthat:
You're right, I am mistaken. It does continue to work as long as I am using a USB power source, but power from my power supply no longer does the trick. This appears to have been an expensive mistake.
You can still use it if you get a 5V regulator (eg. LM7805) and connect it with a USB cable.
byteofthat:
Before I buy and plug in another arduino, can I expect it not to fry if I have my issue with the positive and negative leads sorted?
For the future, if your PSU has 1.7 Volts spare, you can protect against reverse voltage by fitting a diode in series with the positive output.
7.5V+ ---->|---- Vin 5.8V
Any of the 1N4000 series would do the trick and you might even find a few still working, inside some disused gadget with an integrated mains power supply.
Though lastly, I must admit that I am surprised there isn't a different in there to prevent an idiot like me from making this mistake.
You might be interested to read of this
Any intentional reason one isn't there?
To teach kids not to pay attention when messing with electricity
fungus:
Any protection diode would have to go after the Arduino's barrel connector.
Good point. Make that a spare 3.4V and 4 diodes arranged as a bridge rectifier.
Yep. It's an educational board.
I still remember my first lesson, when I attempted to provide the ground for a crystal radio I had cobbled together, by connecting to the Earth of a mains plug. The bang was pretty spectacular!
Thanks for all the advice guys. I went down to the local shop to see what I could do to fix this. I wound up wiring in a 7805 as seen in the attached picture. Seems to be working just great!
But the Due does have a diode in series with the barrel jack.... That's why you should
use the barrel jack, not the Vin pin, where possible (apart from the convenience of
a proper connector).
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