I have some old solar lights I took apart and fitted with some APA102 type leds (rgb, internal driver with 2 wire serial interface) that I am using for some exterior lighting. Each light has six leds in it, and so far I have five lights built and working beautifully with the parts for the sixth one on hand. Unfortunately motivation has been in short supply lately. In the garage I have a PIC16F1828 to send the data to the leds and a PI Zero to tell the PIC what to send to the leds. I kind of thought the PIC might help save the PI in the event of something strange, and it can also handle some basic lighting functions on it's own. Between the PIC and the leds is some Cat 5 cable with three wires at 5 volts, three at 0 volts, and the other two for the clock and data lines. I have 500 ohm resistors on the clock and data lines for current limiting. The three ground wires all go to a ring around the leds that they are all connected to. Due to space I could only connect two leds per power wire instead of another ring like I planned, but in the end it's probably better anyways.

I'd like to come up with some protection for the power wires in the event of a short. I have some 250 mA polyfuses on the power wires for the time being, but as far as I can comprehend they don't like to be maxed out for too long (which I have a feeling I won't discover until something melts). The led datasheet shows 20 mA for each color and 1 mA for internal stuff which would work out to 122 mA per power wire running two leds. Some half amp or less fuses would probably be the simplest, but with six lights and three fuses each light it's going to get bulky quickly. I've also designed the controller to run up to 24 lights which would be 72 fuses in the end if I ever get around to making that many lights. I've thought about shunt resistors and current sensing ic connected to comparators to turn off mosfets and the like, but again it's going to get bulky quickly. My best idea (in my mind) so far is just taking some fine stranded wire, separate the strands, and use a small piece as a fuse soldered between a couple pads on a board. Of course I have no way of telling how much current it will handle before burning and breaking the connection so some experimentation may be in order.

I should also probably consider mother nature and any static she may bring. I have a feeling if any of them get hit by lightning I'm going to have bigger things to worry about since the ones I've built so far are all attached to the house, but what about normal day to day changes?

So in a nutshell I'm trying to limit up to 72 power wires to around 250 - 500 mA each and also maybe add some static discharge or isolation.

Any thoughts??

 

I think I'm trying to make things too complicated. After a little thinking I decided some 10 ohm resistors would do the trick for the power limiting. I was more or less wondering if there is any other strange things I should consider with things being outside in the elements.

Thanks for taking a look.