NeoPixel Circle PCB

The next step in the DMX patio lamp is to create a PCB with the neopixels on it.

The previous posts for reference are:

https://langster1980.blogspot.com/2022/07/designing-dmx-controlled-patio-light.html

https://langster1980.blogspot.com/2022/07/dmx-to-neopixel-arduino-shield.html

I am going for 32 LEDS but I may change my mind. It depends really on the size and spacing achievable as well as current draw and voltage drop.  Lets see what works first.

I'm confident I could design this PCB straight away but it is always a good idea to read through the datasheet and do some calculations...there may be something critical I have missed or didn't know.  I've used neopixel tape several times but I've never really bothered to read up on their technical aspects.

Here is the datasheet: https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf 

The datasheet isn't the worst I've looked at but it isn't the best either...

After some reading...and some more reading here is what I have found:

The package contains 3x LEDS and a control circuit.  According to the research the control circuit draws
8 mA with all the LEDS not active (Off). 

The Red LED draws 13 mA when fully on. 

The blue LED and green LEDS also draws 13 mA when fully on.

Therefore each pixel (3x LEDS in one package) draws 60 mA.  

If we have 32 pixels our current draw with each LED fully on (White colour) will be:

So if the calculations are correct...then we need to account for this 1.6 Amp current draw on our PCB layout. Our connector and wiring also need to handle 1.6 Amps - I'm going to design for 2 Amps to provide a little margin.

Here is the circuit diagram:

NeoPixel Lamp Schematic

Next we need to design a PCB layout.  I'm going for a circular PCB which will fit behind the 84 mm polycarbonate cover.  Lets set the diameter of the PCB to 80 mm - that way I know it will fit with room to spare. I will need a mounting option too...not worked that out yet!  I suspect some stand offs and attached to the cover will work fine.

Here is the PCB layout:

NeoPixel Lamp Top Layer - PCB Render

NeoPixel Lamp Bottom Layer - PCB Render

I added an extra pixel in the centre of the PCB as there was room.  I also added some mounting holes which weren't on the schematic.  The layout went quite well and only took me a couple of hours...must be getting better at this although it isn't because of practice!  I did have a nights sleep between the hours...maybe that helped...

I have exported the gerber files...next job is to get a quote from JLPCB and then assuming the price is right get some boards made.  I'm going to go with black silkscreen.  

I think that's all for now - take care, Langster!