WS2811 LED Pixel Controller

Hello everybody, I was hoping to get some advice on ways to make my circuit better. What I am trying to get working is a pixel controller using the WS2811 LED driver, controlling three MOSFETs, that I can then connect to any size of LED pixel array. I am using the WS2811 because I prefer the single data line control, which I can convert to an RS485 differential signal for long distances, and to take advantage of cables I already have, or leave as single wire between drivers.

Where I’m at currently is using the arduino +5 to supply voltage for the WS2811 and optos, which I would eventually like to bring on-board and have it tapped from the 24v that I will eventually use to drive the pixels (+12v in the interim). I have some 5v linear voltage regulators on order to mess around with. The optos I’ve tried are 4N25 and 6N136, and I have good results from both so far (without a scope I’m not sure how they are actually faring against each other, but results from both seem pretty much the same). The only issue is that they do not respond to a PWM value of 1 from the WS2811 so the initial snap on is a little harsher than PWM straight from the Arduino in to the FET.

With internet research etc I seem to be able to find enough to get myself started, but not enough to figure out if what I am doing is the best way.

The questions I think I am looking to get help on:

  • Advice on implementing the voltage regulator, according to the datasheet I just need the two caps to even the waves
    http://canada.newark.com/fairchild-semiconductor/ka7805aetu/ic-linear-volt-reg-5v-to-220-3/dp/09J6572?CMP=TREML008-005

  • to have the optocouplers able to drive the MOSFETs faster (in an attempt to get them to drive at PWM value 1 and smooth the low end), I either need to be able to drive more current on the optos output (I’m putting ~25mA in, and getting ~8mA out), or have a smaller intermediary FET that can control the source to the 16A MOSFET gate fast enough only using the 8mA from the opto

  • I’m not entirely sure if I am driving the opto output appropriately for what I am trying to do, but applying the +5V to pins 8 and 6 on the 6N136 seems to be working (except for PWM of 1)

The basic premise is working, I’m hoping I can improve on what I’ve got working before I look at ordering a small number of PCB’s and assemble a couple of boards. Thank you for any help and advice :slight_smile:

*edit: When using the 4N25 I am not applying +5V to pin 4, I have it drawn on the schematic but have not exchanged the part for the 6N136 before uploading, with the 6N136 I am applying +5 to pin 2 through the current limiting resistor, the WS2811 PWM sink is on pin 3, output side is +5V to pins 8 and 6, with pin 5 ‘grounded’ to the MOSFET gate pin with the 10K pull down resistor. Apologies if I am being confusing.