Power Supply for Small Barrel

I’m looking for some help for a power supply. The unit says it is DC5V. I thought about looking Fritzing for some possible help regards the amps and other specs. I find only ones that marked as 5.5 mm barrel. The one I’m looking to power is probably 3 to 4 mm barrel.

Arduino Uno on the bottom and the board on top is what I need the power supply for.

Any help much appreciated.

I’m not sure I understand your question. Assuming that is a Uno on the bottom, it has (typically anyway) a 2.1mm barrel plug in which it wants to see about 9V to power the on board 5V and 3.3 volt regulators. The device on the top looks to have either a 1.3mm or 1.7mm barrel connector (from the apparent size I’d guess its 1,3mm but screens are deceiving :slight_smile) . Where does the 5 volts enter the picture? Does the device on the top want 5 Volts in to the power jack?
The capacity of the power supply is unrelated to the size of the output jack, to find its capacity you would need to either find a plate on it that lists its input and output voltages and currents or find a part number and google for a data sheet.

Peter Van Epp

Sorry, I’m looking for a power cord, plus into a wall, for the board depicted on top in the image.

On the cover which covers the top board, it says DC5V on it.

In order to purchase the power cord, I thought I might be able to use the Fritzing app to obtain some specs/data sheets. I don’t see anything on the actual part for numbers.

Ah! So you have a couple of issues: you need to know how much current it needs (solvable by giving it a supply with too much, as it will only take what it needs) and most importantly to know which pin on the barrel connector is positive. Usually (but not always) the center pin is positive. Connecting it up backwards will likely blow the device. Assuming the USB connector on the device is powered by the device, the ground pin on the USB connector (a USB breakout board would be the easy way to find that) should connect to the 5 Volt ground. An ohmmeter connected to USB ground then to the two pins of the barrel connector in turn should maybe identify which one is ground (making the other the 5V pin). If you have a 5 V supply and an ammeter, after determining the polarity of the power jack you could feed it 5 volts from the power supply and measure how much current it draws (check that the voltage remains 5 volts too, if the device draws too much current the supply voltage may drop as well). Then find a wall wart with at least twice that current capacity and regulated 5 volts and you should be away (either find one with an appropriate barrel jack or solder a new barrel jack on to the wall wart). Note that some or all of these steps may damage the device (if for instance it wants too much current and the input voltage drops and the device doesn’t like under voltage), so only do it if you don’t mind perhaps damaging the device. Hope this helps.

Peter Van Epp

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Thanks for the reply Peter. that gives me lots to think about.

How exactly are these things measured? What does the 5.5 mm mean?

I think that is probably the barrel outside diameter from the 2.1 connector data sheet I just pulled up.

The inside diameter is the 2.1mm that they are sold by usually. As I said from the size relative to the 2.1 on the Uno I think you are looking for a 1.3 mm, I use them instead of 2.1mm for my 5V wall warts so I can’t plug a 9V 2.1mm arduino wall wart where a 5V wall wart wants to go. If you have a local electronics supplier you should be able to get a 1.3 mm jack for a couple of bucks and try it and see if it fits. Once you have that connection, without powering it you can try the various pins on the usb connectorwith an ohmmeter to see if you get a connection which should identify ground.

Peter Van Epp

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