OctoPi mods and lighting...

[The Chairman]

Maybe place a mosfet directly on the pcb to control the LEDs?
Adds one more connection from the pi to the pcb but avoids additional parts for controling the lights.

It won't draw over 300ma, so I should be fine. A mosfet wouldn't help at all on the 2812s.

 

[Oitzu]

I meant for turning the LEDs on and off via Software. Afaik the gpio Pins of the Pi deliver 16mA max.
I was under the impression that you use simple dump pure white LEDs for your board.

 

[The Chairman]

The pins can provide up to 500ma. I can't find if this can be through one pin or not. I will be driving the light with the 5V power pin, which can provide ore than an amp. I might be using a relay connected to one of the switching pins to make it switchable on or off.

 

[Oitzu]

I would be impressed if the gpio can handle 500mA without that the bonds of the SoC let the magic smoke out.
Yeah i was suggesting a mosfet instead of the relay because it could also handle pwm for dimming.
But carry on.

 

[The Chairman]

OK, I have plenty of time... do you have any links to mosfets and how to use them? I've never used one, but I'm happy to learn.

 

[Oitzu]

RGB LED Strips
This adafruit tutorial has a example with an RGB-LED strip. I think it shows the basic principle close enough.
You basicly break your circuit on the ground side and insert a N-Channel mosfet there.
When you apply voltage on the gate the mosfet gets conductive.

 

[The Chairman]

That's a HUGE transistor. I want a tiny SMB that I can plant on my LightRing.

 

[Oitzu]

You can lay down a TO-220 package on the pcb.
But there should also be other smaller surface mounted mosfets that can handle that current, out there.
The TH components are prefered in tutorials because they are easy to use on breadboards.
I can look a little bit around if i find a fitting one.

 

[The Chairman]

I have settled on the FDV305N transistor. Thanks to Joe D from Gainesville Hackerspace for his incredible patience in designing and redesigning this ad nauseum. I have lost count of how many iterations I have gone through. I moved a few resistors around and justified the holes to be at right angles to the center line through ScubaBoard.com and center. I learned how to clean up the traces so they don't seem so spasmodic.

 

[Oitzu]

FDV305N looks, on the paper, like a good fit.
Great work!
One suggestion, that doesn't matter for you now, but could be great if you ever want to mount an connector to the board:
You could combine the 3 connection points to one connector with standard spacing.
In schema that would be CONN_01x03 with footpring Pin_Header_Straight_1x03.