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I've got a 16 Pixel neopixel ring and a Digispark 2 board.

I've also got a 5V 2A USB wall adapter.

Ideally what I'd like to do is connect the USB connector of the Digispark to the USB wall charger and use this to power the board, then use the 5V and GND pins of the Digispark to power the neopixel ring.

My concerns are the ~500mA restriction of traditional USB ports. I'm not sure if this comes in to play when using a wall adapter.

I also don't want to fry anything, so just wanted some opinions.

Thanks a lot

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When using a wall adapter the most important rating is the one on the adapter.

If you are soldering something to another something that had a USB connector it might be a good idea to put a label onto it "Warning, uses more than 500mA" in case in 3 years you think "Hey, plug that in!". That said, any PC/Laptop built 2005-ish or later should have protection circuitry that just switches off the group of USBs that has the overloaded port, as per the standards prescribed for that.

One thing to watch out for is thin, flimsy wires, like those cheap 50cent USB charge cables. They will gives you voltage drops that'll make you cry at 2A. The one cable you should be able to fully trust is the cable that came with the charger/phone, as that should be dimensioned for the total 2A.

Again there, the main risk is of things not working as expected, something wanting 5V might get only 4V if you go over 500mA with a very cheap thin wire, 9 out of 10 cases it'll just not work or work badly.

All in all: Go for it, but always remember it might exceed USB standard drain and as such never turn an idea-train like this into a mass product before researching the required power sensing standards. But for one-offs, toy away!

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  • \$\begingroup\$ Thanks for the advice. Much appreciated. I think I'll experiment with running everything from the USB connector and then also from another source on the 5V pin, see if convenience wins over possibly less reliability ;) \$\endgroup\$ – Mitchell D Jun 1 '15 at 12:42
  • \$\begingroup\$ @MitchellD As long as you don't at some point try to inadvertently power a laptop through its USB plug, I'm not sure if the standards prescribe any fail-safes for that ;-) \$\endgroup\$ – Asmyldof Jun 1 '15 at 12:47
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The 5V port on the digispark is connected to the output of an onboard regulator. It has a 500mA max output. They recommend using a heatsink for anything over 200mA. Applying power to the USB connector bypasses the regulator, making it's current limit a non issue.

There is a diode between the 5V bus and the USB 5V line. I don't know if that will be an issue.

The led ring draws 18mA. I'm assuming that's for each led. So it needs 288mA to turn all 16 LEDs on.

I don't see any problems. Light it up! Good luck

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