How are LED Fairy lights are wired?

[hamster_nz]

Before I start cutting, does anybody know how inexpensive LED fairy lights are commonly wired?

I've got a set of 100 LEDs , that are connected to a 31V controller using two wires. They can blink alternate LEDs for flashing effects. So I assume the LEDs are in alternating polarity.

The string of 100 seems to be in 10 groups of 10, where there is a third wire running between them (9 links with three wires, than one with only two). The last 10 LEDs only have two wires.

I assume means that they are 10 parallel strings of 10 LEDs in series, each string having 5 LEDs wired A-K the others wired K-A.

So how exactly does that work? Without anything else, one set of LEDs will prevent current flowing into the other five. Does each LED have a standard diode back-to-backed with it, so current can still flow? What limits the current in a string? Is the PSU acting as a current source? Are the LEDs actually 'smart' in some way? THere doesn't appear to be anything else where the LED is connected? Is there special 'fairy light LEDs' that have an inbuilt reverse voltage bypass diode (the volumes made would be high enough to make them I guess)

[tpowell1830]

Very hard to answer, as they are different configurations. BigClive is always breaking these down.





Hope this helps...

[hamster_nz]

Finally got some time to look at this. They are wired as 10 LEDs in parallel, repeated 10 times.

Which is actually quite helpful - you can split them off into  sets of ten, then drive them from 5V logic with about 100 Ohms or so of resistance to limit current.

I'm somewhat abusing the outputs a 74HC04 to drive them, but it works quite well.