Due controlling WS2811 strips driven with external power question

Other Hardware LEDs and Multiplexing
1

I have a problem I'm facing that I'm not sure how to figure out.. Any help would be greatly appreciated.

Part of my project includes a Due driving 14 1m WS2811 LED strips (60 led/m)..so a total of 840 rgb leds. I have an external power supply to drive these strips rated at 5V/60A, which should give me plenty of juice, especially given that I will be using only 1/4 brightness at most and not all the lights are on at once.

While I've been developing the code, I've been testing with a single 1 m (60 led) strip hooked up straight to the Due 5V out as shown in the attached diagram (ThisWorks). This worked well and I did not experience any issues with the led strip or any other components of the project.

Now, that I've got the code finished up, I am getting ready to test multiple strips driven by external power supply I mentioned above. First, I'm trying with a single strip. I've hooked up the external power to that 1 led strip through a 1000uf 10V capacitor. All the grounds are tied together as shown in the second attachment (DoesNotWork). Now, when I turn everything on, the led strip is completely misbehaving, lights flickering in different colors and sporadically (everything else works..there's an mp3 sd card player and msgeq7 ICs).

Multimeter at the power supply shows it has 5.4V and running just fine. I'm at a loss as to what to check next and am afraid of frying something.

Also..I've tested this with a Mega previously and it worked as expected with the same external power supply. Could it be the fact that I'm using Due to drive the whole thing now?
Although, I'm not sure how that would affect things, but I'm just starting in electronics and I know there's a lot of concepts I'm still misunderstanding..but I'm reading and experimenting a lot.

Any help or advice would be much obliged..Thanks in advance!

DoesNotWork.PNG
DoesNotWork.PNG1077×670 132 KB

ThisWorks.PNG
ThisWorks.PNG1063×564 120 KB

2

Ok, so I tested the same code and setup but using a Mega 2560 and it worked as expected. So, apparently the voltage difference on digital pin-out going to the DIN pin of the strips is what's causing issues with Due being at 3.3v and Mega matching the strip power at 5v.

Next question is, how do I fix that?

Can I step up the voltage from the digital-out pin from 3.3v to 5v, and how? Can I use a mosfet, or is there a better way?

3

Hello. Yes, use a mosfet or a bjt. Doesn't need to be a high power transistor, its only a data line.

Paul

4

PaulRB:
Hello. Yes, use a mosfet or a bjt. Doesn't need to be a high power transistor, its only a data line.

Not 100% sure how to wire that up. Attached a diagram, please let me know if that looks ok?

Thanks!

WithMosFet.PNG
WithMosFet.PNG1236×810 158 KB

5

You might struggle getting that transistor to work at the 800KHz region needed. I always use a 74HC14 or 74LS14 to buffer the signal.

Strip driver.jpg
Strip driver.jpg1171×621 54.5 KB

6

Thanks for the reply Grumpy_Mike! I'll try the approach you mentioned.

For now, I've attached the circuit that has been doing the trick for me so far. (from here)

I will give it a shot using the 74HC14 as I happen to have one. It's always good to have options.

Thanks again!

3vTo5v.PNG

7

I wouldn't use that circuit as:-

  1. It has a 10K output impedance.
  2. You are over volting the logic output.

You may get away with it for a time but it is long term damaging your Due.

8

Good day from South Africa.

I trust you are well and healthy in this uncertain times with the corona virus

I am trying to get my mega 2560 working.
There are so many info on the web, it is a real information overflow.

Could you assist me in the programming please?

For a test I have a 24LED ring ws2811.
The end result I would like is 20 strings of 15 LEDs each in a circle

Any help will be appreciated
hendrik.botha@centrade.co.za

9

This is a reliable source of information I would follow this