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I found this outlet plug deal at the dollar store for like ten bucks. I only bought it to open it up and have a look-see inside. Found this 110v AC to 5v DC circuit, as you'd expect. USB data lines don't run to anything (good!). The +5v lines aren't isolated from each other, so it's really just the one line shared by both ports. The wires hanging off went to the mains.

Would this be an okay circuit for a DIY Arduino project? Just needs to power the little AT board and a relay for switching on and off 110 to a heater coil periodically. Been wondering how I was going to do power supply for that project, and I like this little form factor. Probably end up removing the USB ports and just solder wire to the board.

I found this outlet plug deal at the dollar store for like ten bucks. I only bought it to open it up and have a look-see inside. Found this 110v AC to 5v DC circuit, as you'd expect. USB data lines don't run to anything (good!). The +5v lines aren't isolated from each other, so it's really just the one line shared by both ports. The wires hanging off went to the mains. Would this be an okay circuit for a DIY Arduino project? Just needs to power the little AT board and a relay for switching on and off 110 to a heater coil periodically. Been wondering how I was going to do power supply for that project, and I like this little form factor. Probably end up removing the USB ports and just solder wire to the board.

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[–] • 1 pt

To test the current you'd need to put it on something where you could increase the load until it goes into shutdown.

Quality of the parts is hard to tell until it quits...

[–] • 1 pt

Alright... So basically I can try using it, and if it doesn't work then it doesn't work. Would there possibly be a failure mode that compromises my Arduino? It's not like they're expensive or anything, but I'd rather not ruin one if I can help it.

[–] • 1 pt (edited )

If the supply was designed decently, it will probably just shut down if you try to draw too much current from it. You could measure the DC voltage output as you apply it to the arduino, if it sags considerably or goes to 0VDC then you know you've overcurrented it.

Another thing you can check is for AC ripple on the power supply, measure across the output (under load) just like you'd measure DC. If you see a large amount of AC voltage (hundreds of mV) then it may not be suitable for use in a digital circuit. I've had some USB supplies that had enough noise on them they'd charge a device, but would make things act funny (touchscreens) while charging.

It shouldn't hurt your device. That's not a given, however.

[–] • 1 pt

The good news is that my Arduino board has some DC smoothing circuitry built in, so noise might not be that big of an issue (I think). But that might only be on the barrel jack side of it which can take a range of volts. It can take power from that or USB, and I don't know if that circuitry applies to both supplies.

I have a multimeter though, and I do need more practice with it. Guess I'll try wiring it up and do some measurements. I don't have a scope yet, but it's on the 'eventually when I have more space' list.