Trouble with some WS2812B LEDs and my mkr1010 wifi

ok I'm not sure what's going on here, but I'm currently in the middle of making an oversized 7 segment display clock using a total of 172 WS2812B's.

I've got each digit wired up properly... ran the Adafruit Neopixel sample code to test and all 21 LEDs per digit lit up in the manner they were supposed to.

I then connected 4 of these digits together, and again everything lit up properly as expected.

that's where my trouble then began. Due to some stupidity on my part I thought my arduino would be more than capable of powering 172 LEDs. of course it wasn't. it would either light about 100 or so, and reset, or it'd light them all, but dim once it hit about 100 pixels.

so I then added a secondary 5v USB power, and connected the LEDs directly to that and just ran the data signal from the arduino to the LEDs. from there, all LEDs just lit up in random flashing patterns. not in the order they were supposed to from code.

I ripped all the interconnecting wiring out and got it back to it's original state. since I figured originally I must have cross wired things somewhere, I went back and reconnected the LEDs to a separate 5v 12A PSU. again all the lights seem to be going haywire.

what am I doing wrong here? I read and figured the arduino wasn't capable of powering that many LEDs, and other suggestions have said I should use a separate power supply, and power the LEDs at different intervals. which I'm now doing. I've got about 42-44 LEDs powered in parallel off my PSU, but since I didn't modify the data line, there's no reason I can see that the lights should be going crazy. do I need to put the 5v and gnd from the arduino into the LED strip as well as the 5v 12A PSU? seems a little odd to do that, but I've no idea what's going on

any help would be greatly appreciated.

Thanks!

All you really need is the data + ground lines to the neopixel. The LEDs can be on their own PSU

No experience with this board, but strange things could happen when you try to control a 5volt-logic WS2812 chip with a 3.3volt-logic processor. A level converter chip should be used in between.
Leo..

Just the ground. The LEDs won't be able to make sense of the data signal from the Arduino if they don't share a common ground.

Don't connect 5V from the PSU to the Arduino if you are powering the Arduino some other way, e.g. usb. No two 5V supplies are ever exactly 5V or exactly the same as each other. If you connect them, whichever is slightly lower than the other could be damaged.

It's ok to connect the 5V PSU to the Arduino 5V pin if you want to power the Arduino from that PSU also. But make sure to disconnect any other power supply to the Arduino, e.g. usb.

thanks everyone. connecting the arduino's gnd pin to the 5v PSU sorted it all. very much appreciate your assistance!