8x8 WS2812b matrix save current draw through Arduino

Hi,
I'm planning to run one of these 8x8 CJMCU-64 RGB Matrix through arduino nano (usb).

I tested it current draw powered via 5V-5A power supply, and through Arduino (usb). All leds White.

Current draw, at % brightness level, in software that I'm using to send data to it:

At 100% brightness lvl 1.25A (PSU) - 0.65A (usb).
At 50% brightness lvl 0.92A (PSU) - 0.53A (usb).
At 40% brightness lvl 0.82A (PSU) - 0.49A (usb).
At 20% brightness lvl 0.5A (PSU) - 0.37A (usb).

My question is, what % should I aim for powering it out of USB (not to overwhelm Arduino voltage regulator) for save long term use.
20%- It wants to draw 0.5A at that lvl powered via PSU
40%-50%- It draws 0.5A at that lvl powered via USB.

Thanks for your help good people.

Powering an UNO via USB there's no onboard voltage converter involved.
0.5 Amp is at the spec of USB.
Try using 10 - 15%.

1 Like

Powering through the USB connector does not involve the voltage regulator.

Just as well, because with almost no heatsink, the on-board regulator is basically useless anyway. :roll_eyes:

On a Nano, there is a diode generally rated at 500 mA between the USB connector and the "5V" pin. But you simply should not attempt to power your matrix - which draws 250 mA even when completely dark - through the USB connector. Just don't do it! :astonished:

You connect your 5 Amp power supply - which is correctly rated for the 3.6 Amp draw of the matrix with all pixels full white - directly to the matrix. You then connect the three connections - 5 V, data and ground - as a bundle back to the Nano with the 5 V connected to the "5V" pin.

That is the only correct way to wire and operate it. :sunglasses:

Any idea why did it drew 1.25A not the 3.5A both you and manufacturer are saying it should have? I had a lot of overhead being connected directly to 5V-5A PSU.
And that its in worst case scenario with all LEDs white.

10% is not completely dark, it is uncomfortably bright when directly in front of you.

Please make a little drawing before anything is damaged. Misunderstandings are not too far away.


Like tthis.

Don't know - your code is surprisingly invisible to me!

Hmmm, what does that mean?

No doubt!

Note that your diagram shows the Nano ground going to the power supply ground instead of correctly to the LED strip ground as a pair with the data line. And you can connect the 5 V from the strip back to the "5V" pin on the Nano to power it - the voltage drop in the diode will then prevent it drawing power from the USB.

It is important to run all three connections together, though this is not a cause for any of the current concerns.

Hi,
Thanks for reply.
Unfortunately I read it now and I knew I won't be able to sleep whole night because of it. So I went and did it.

Current draw was still the same. 1.25A.
After connecting 5v to Arduino s 5v pin, it actually dropped to 1A.

Przetwarzanie: PXL_20210815_072220561.mp4...

No idea what that is supposed to mean! :worried:

You have no capacitors connected to anything therefore you amp meter is trying to measure a pulsed signal, even on so called full white, and in general they can’t do that accurately.

That is certainly a possible problem, except that on full white it should not be a pulsatile signal - on what basis are you suggesting that?

And there is no reason even on partial brightness to expect that the PWM of 64 LEDs will synchronise to any extent, so it will generally average out.

I was trying to upload a video, but it didn't work I guess.

I did a little test, and I run those at full power (white) through Arduino usb powered only.
Reading 0,65A for 12h straight, and haven't encountered issues.

Btw shouldn't I be at 0.9A limited plugged in to usb3?

Edit;
Uploaded to yt. test - YouTube

Observation with an oscilloscope of a full white WS2812 strip with no capacitors.