On decoders, it's because a current sink is much more efficient (smaller physical part for same current capacity) than a current source. What the function on a decoder do is basically turn a switch on that connects to ground. A secondary bonus is that if you need a light to go on any time any of two different functions are on - you can just wire them together. IE< if the decoder has directional lights, adn you just want a headlight, and the decoder doesn't allow changing that, you can hook a single light to both the white and yellow wires. If either one or both are on, the light is on - and this does not in any way harm the decoder. Current sinks are designed to work this way. It's also a more efficient circuit design, less loss (heat) than a current source.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinker I know it sounds backwards but it has been correctly stgated. The BLUE ire on a decoder is common, but it is a POSITIVE common. Each individual function wire, white, yellow, violet, green, etc. is the minus side of the circuit. There's a very good electrical reason for that, if anyone is interested. --Randy
I know it sounds backwards but it has been correctly stgated. The BLUE ire on a decoder is common, but it is a POSITIVE common. Each individual function wire, white, yellow, violet, green, etc. is the minus side of the circuit. There's a very good electrical reason for that, if anyone is interested.
Reminds me of the courtesy lights on GM and many other vehicles. An always hot positive going to the lamp and the other leg could be grounded in any number of places (door jamb switch, dash switch, etc.) to make the light(s) come on. Very simple and reliable!
Ed
I would love to hear the explanation because it always seems back-a$$ward to me and I work on electronics for a living. Please post or PM me and let me know.
Long lead = +ve = anode = blue wire
Resistor can go on either leg, though out of force of habit I tend to put it on the cathode
Simon Modelling CB&Q and Wabash See my slowly evolving layout on my picturetrail site http://www.picturetrail.com/simontrains and our videos at http://www.youtube.com/user/MrCrispybake?feature=mhum
It doesn't really matter. Just make sure that the resitor is in series with the led and not across the leads in the circuit. You might want to refer to this website for further help. The long lead is the anode. The cathode should go to the output on the output of the DCC board and the anodes should all go back to the common.
OK, I'm going brain dead here.
Does the resistor go on the long lead or the short one?
Is the long lead the anode or the cathode?
Does the long lead go tothe power or the common.
It's been awhile, and I'm losing my memory...
Van Hobbies H1b, K1a, T1c, D10g, F1a, F2a, G5a. Division Point: H24-66 Hammerhead, Alco covered wagons A-B-B-A, C-Liner A-B-B-A, EMD FP7A A-B-B.
H1b modified to replicate modern day 2816. All with Tsunamis.