8x32 LED Panel (WS2812B) Power Requirements

[Ian]

I've bought a 8x32 flexible RGB LED panel from AliExpress to have a tinker with, as it looks like a fun way to improve my Arduino programming skills (and no doubt useful for a project in the future).

It looks like each LED can use up to 3x20mA (60mA for white) of current, so 256x0.06 = 15.36A if all LEDs are set to white at max brightness.

I'll be using this indoors, so the brightness levels will be waaaaay lower than max - plus I'll likely only be using up to half of the LEDs at any one time (perhaps all in white, likely another RGB mix). Normally I'd just use a 5V 20A supply and be done with it, but I've not got one to hand and would rather avoid a beefy supply for what I'd hope to package in a small enclosure.

It looks like if I use the FastLED library (http://fastled.io/), I can limit the current using "set_max_power_in_volts_and_milliamps" - so I can set this based on the power supply I use.

Based on a what I've read, 6A sounds like it should be plenty of current to drive the number LEDs at the brightness level I'll be using. However, my concern is that the WS2812B uses PWM dimming - so do this mean that I'll still need to cater for a higher max current usage no matter which brightness I use, or are the LEDs pulsed out of phase with eachother? i.e. are all LEDs going to be pulse at the same moment, meaning I'll need to provide for a higher load.

Any thoughts would be very welcome .

 

[BobK]

Good question.

There is nothing to syncronize the LEDs, so it is likely they will have random phases, and with that many , should average out.

I might try an experiment later to monitor the current with my scope.

Bob

 

[Ian]

Thanks Bob - have you got the same panel or something that uses the same driver?

I've still got a couple of weeks until mine arrives from ChinaPost

 

[BobK]

I have strips, they will work the same way, since it is the same chip WS2812B.

I am running a strip of 60 off a tiny Li ion battery, using max 100 of 255 which is plenty bright indoors, and the typical current, measured with multimeter is 300-400mA.

Bob

 

[Ian]

Thanks Bob, really appreciate that . I'll get a 6A supply and give that a whirl (and limit the max. current in FastLED to 5A for good measure).

 

[BobK]

Here is a screen shot from my scope measuring the voltage across a 1Ω resistor in line with the battery. It is running a 60 LED strip. As you can see, the current varies between 200 and 400 mA with a period of about 2.5mS. All of the LEDS on the strip are on with different colors of the rainbow with the two of RGB adding to 100. The calculated average current ought to b 470mA, so, in this case the peaks don't even reach that.

 

[Ian]

Cheers Bob, that's good to know, as I'll likely be using them even dimmer. Once the panel arrives I'll run some tests and report back (may take a while, as China post takes ages).

 

[Ian]

The parcel finally arrived, so I've fired up the display with a quick test via an ESP8266, mocking up some text and an icon. With the brightness level and number of pixels I'll likely be using, it looks like I'll be topping out at 250mA - far less than I had feared . I think I'll just power this via USB to keep things simple .

 

[Harald Kapp]

Care to show a photo, Ian?

 

[Ian]

Sure! Here's a quick animated GIF - the scrolling text reads ElectronicsPoint.com, but it's quite bright so it's hard to read:

In a couple of weeks I hope to have time to work on a project using it, so I'll document it in full then. I'm hoping to make a display which scrolls through lots of relevant stats for the day (weather, unread e-mails, to do list, calendar, etc...). It'll adjust brightness to compensate somewhat (via LDR), rotary encoder to manually scroll through entries, plus as much of it as possible will be 3D printed .

 

[Harald Kapp]

Nice, thanks for sharing.

This display combines with an octolively kind of sensor array could be a great display,

 

[Ian]

This display combines with an octolively kind of sensor array could be a great display,

That looks fantastic! I think integrating an array of IR proximity sensors with the WS2812B panel would be beyond my skills at the moment, but I really like the look of this, so perhaps it's something I can try in future. I imagine a full wall of these things would be great fun (and trippy!).

 

[Harald Kapp]

I imagine a full wall of these things would be great fun (and trippy!).

What would the wife say, though?

 

[Ian]

What would the wife say, though?

Haha, funnily enough I think she'd probably like it more than me