LED wiring question

[mccoy178]

Im building two CP's at once, and as I was soldering the sixty resistors to the sixty leds, I began to wonder; do I have to use shrink tubing or something similar?  Is it likely I would have a short or get a shock?  I just wondered what others thought on the matter.  If I have to shrink tube all those led's, I just want to know it's a worthwile effort.

[Ed_McCarron]

"do I have to use shrink tubing or something similar?"

It's not a bad idea.  The leads on the leds are pretty stiff - you may be able to get away with just bending them out to prevent touching leads but its one of those problems that will get you eventually.  I've even bent 'em apart and covered in hot-glue.

"Is it likely I would have a short or get a shock?"

Not really enough voltage to shock you (unless you are really trying - lick it and you are on your own) but it'll short every chance it gets and risk damaging something expensive.

[tetsujin]

I would do one or two things differently -

First, rather than soldering to that many LEDs I would probably prefer to solder to snappable pin sockets, and then plug the LEDs into those.  That way if I screw up a polarity (it happens!) or whatever, I can swap the LED easily.

Second, instead of using individual resistors I'd probably look into multi-resistor packages.  You can get DIP-packaged resistor networks (multiple resistors tied to a single line, for instance, or just a bunch of resistors in parallel if you prefer - the disadvantage in the former case is that you need to run two lines to each LED rather than one line and a common ground - but I think running two lines would be simpler anyway, don't have a mess of ground wire everywhere.) - you save a bit of board space compared to mounting individual resistors on a board (doesn't sound like you were mounting the resistors on a board anyway) and if the resistor package ties to a single line then you also save soldering work.

Third, the risk of a short circuit between or across LED lines can be mitigated somewhat by having the resistors be "upstream", as close to the voltage source as possible.  That way if there's a short anywhere between where the resistor is and where the LED is, the voltage will still have to cross the resistor before reaching the short, so the LED won't light but most likely nothing will burn out, either.

[RandyT]

Third, the risk of a short circuit between or across LED lines can be mitigated somewhat by having the resistors be "upstream", as close to the voltage source as possible.  That way if there's a short anywhere between where the resistor is and where the LED is, the voltage will still have to cross the resistor before reaching the short, so the LED won't light but most likely nothing will burn out, either.

This is good advice and will prevent problems caused by a temporary wiring problem.

Just for kicks, I put a 1/4 watt 100ohm resistor across the 5v supply on my PC.  No fireworks, but it does get uncomfortably warm after a few minutes and the longer it was hooked in, the warmer it got.  Smaller resistors will get hotter faster.

I've seen very small resistors glow bright orange when I've accidentally hooked up things incorrectly in the past. 

Be smart and insulate your wires or physically keep them from being able to short together.  Very bad things can happen to your hardware or you could even start a fire.   

It's really not worth cutting corners with this type of thing.

RandyT

[mccoy178]

Thanks a ton.  I hope the led's you are going to sell are out of the box ready to be wired up.  That would be a great help and worth the cost since I've done about sixty of the things.  I am planning on using leaf switches on my personal cp and I can't imagine doing sixty again.