5v power and WS2812 LEDs

Using Arduino General Electronics
#1

I made a lamp for a friend that runs 50 WS2812 LEDs from the 5v line on an Adafruit Pro Trinket.

I've run 44 before in this way without problems...but though the lamp starts up fine, after it's warmed up a little the LEDs start to flicker, especially if set to "all white" (255,255,255).

I think I'm overloading the 150mA that the 5v line can give, so I need a separate power source. However this is a problem as the lamp is designed to give access only to the micro USB on the processor, and changing that effectively means starting from scratch.

I believe there are "power pads" under the chip...but I've no room to solder on a JST connector. Is it possible to solder directly on to these pads, and will they deliver higher than 150mA if I do?

If not, is there some other way I can take a +ve and GND directly from the micro USB to power the LEDs and take advantage of the 1500mA capable input there, whilsts still powering the Arduino from the same socket?

#2

20mA per color is 60mA for white x 50 is 3 Amps.

#3

Yep...which is why for the white setting I only turn on every other LED (it's still plenty bright enough), so that gives 1.5 Amps = 1500mA...I just need to know if I can get that from the wall socket I use, and still drive the processor without having to rip the entire assembly apart and start again.

#4

Well, providing an answer is a little dodgy because I can't see your setup, [try reading: http://forum.arduino.cc/index.php?topic=149015.0] but if I were doing this, I would have only minor compunction about soldering directly to those two little pads, on the underside of the board, that seem to be there for just such a thing, and then running that to the WS2812 strip. And, I would be sure to plug into a USB port that can deliver at least 1500mA [and for giggles, I'd make sure it was a little more].

I would also consider that, because these are not through hole pads, they could easily peel off--especially if I applied too much heat when soldering. For instance, I would do something to anchor, or strain relief those wires--like, maybe, by tie-wrapping them to the board. But, maybe this is not such an issue, if the assembly will just be housed in a lamp, with no chance of them ever moving ever again :wink:

Also, I would make sure to reach a good compromise between wire size, and practicality of soldering to such small pads. Since we're talking an amp and a half, I would want the wire size large enough to minimize any voltage drop across the wires. Maybe smaller wires soldered to the pad, spliced to larger wires for the run to the LED strip.

I might even consider connecting those wires to the center of the strip, rather than one of the ends of the strip. That way, the current will divide, and only a max of 750mA will ever flow through a WS2812 chip [not as much of a deal, if the power and ground is delivered by an auxiliary trace -- and not by a daisy chain through each WS2812].

But, then, I could be wrong, because I'm shooting in a dimly lit arena.

#5

The 5v line?

I'm not too sure how the Adafruit Pro Trinket operate I guess... is the +5v line.. AFTER the regulator?

WHat are you using to POWER the thing?

You could use a phone charger/micro USB cable.. to 'power' the Trinket.. and tap into the VIN line.. (which if you are using a regulated 5v power source)..should give you +5v but more current.. as it bypasses the voltage regulator (ie: direct VIN source)

#6

Thanks for advice and appreciate I didn’t give a lot of detail...because I didn’t know what detail to give.

That said, followed the advice that WAS given by using the USB Bus output (1500mA) instead of normal +5v line (500 mA). Balanced rest of shortfall by limiting parameters in sketch such that either not all LEDs are on, or if they are, not at the full “255 255 255 RGB” brightness.

Result; working lamp and happy mate who is delighted with it...

Thanks all once again.

#7