Ian,
Thanks for the candid response.
My lack of knowledge about computer power supplies (CPS) is exactly why I'm asking. I don't mind messing around with typical battery power, but as soon as I plug something into the wall, I want to be sure I'm careful.
OK - Thanks for taking my comment the way intended..... We'll get there!
I've heard about people using "wall warts", laptop power supplies, and computer power supplies for various purposes. So I'm exploring the possibility.
They'll all work in that they supply low voltages from a mains (110v or whatever) input - The key is knowing two things that are always printed on them somewhere - The output voltage(s) (DC, we don't want any AC here) and the current capability.
"Typical" wall warts range from ~2v to 20v and 50mA to 500mA.
The CPS I'm looking at right now says it outputs;
+5v @ 25A [
]
+12v @ 10A
-5v @ 0.5A
-12v @ 0.5A
Note that the first two are particularly powerful - The +5v output is 50X-100X the power of the typical wall wart...... Be careful!.....
I do have an old HO power pack. My original plan was to wire my led's so that I could set the DC output of the power pack at about 5 or 6 volts then take the knob off so I don't accidentily turn it up and fry my lights.
Ahh, the old "suck it and see" approach! Nothing wrong with that, and there's a lot to be said for adjustability - You could even set different levels of lighting based on time of day.....[And/or instantly let the smoke out of every light on your layout
] More below.
Just thinking that a CPS would give me more capacity.
Oh, it will! - *LOTS* more! As you can hopefully see from the above.
If a power pack will meet my needs, I'll probably stick with that. Any idea how many LED's I could run from a typical HO power supply? Even if it's a ball park... Is 100 too many?
"It depends". A reasonable starting point is ~20mA per led - So, 100 x 20mA is 2000mA, or 2A - If your supply can deliver 2A you're good to go. BUT, you've got to decide how to wire 'em (parallel or series or a combination of both).
I guess (always dangerous!) it's a maximum of 12v DC. What does it say for current? [It'll be either "X Amps" or "X VA" - We can work from either value.]
Do you have a multimeter? [Don't need anything fancy]
Returning to answer your original question - You are indeed on the right track with your little circuit diagram - You've got +5V coming in to the anode (the long lead, opposite the flat on the led) and eventually going to ground - Very good.
-5V OTOH would reverse your diagram - Feeding them from this you'd put the -5v at the bottom and ground at the top and they'll work the same - Current always flows to ground, and you want it going "the right way" to light the leds. [Having said that, mixing +5v and -5v will lead to confusion and, almost certainly the "magic smoke" being released at some point....]
HTH, cheers,
Ian
