Hi all,
I am working on installing en ESU Loksound Select into a Proto2000 GP7. I got the decoder and a Zimo 8 ohm sugar cube the other day, and they seem to fit just right. I have been told it is necessary to replace the incandescent bulbs with LEDs, so I ordered some warm white 3mm round LEDs and some 1K Ohm resistors. I am wondering if the resistor should be placed in series on the blue lead or the white lead of the lighting wires?
Thanks for any help.
-Christian
It doesn’t matter which lead it is on nor in which direction the resistor is in the wiring.
Which lead is the positive lead? Just need to know to so I don’t wire the LEDs backwards. Thanks!
-Christian
The longer one.
Christian,
Some good stuff here:
http://www.sbs4dcc.com/tutorialstipstricks/ledlighting.html
Google LED lighting for DCC model railroad and you will get tons of information.
This image always comes in handy for me:
Have fun, Ed
Really sorry for not clarifying. I meant is the blue or white lead positive in the locomotive?
-Christian Javier
Hi Christian
The blue lead is the positive. It is often referred to as the ‘common’ because all of the LEDs that you install in the locomotive will have their positive leads connected to the blue wire.
Dave
That used to always confuse me because household electricity books often refer to the neutral white wire as “common” since all of the neutral white wires from the various circuits are ground to a common bus on the service panel.
When I started installing decoders in my locos, I could not get used to the fact that the common was the positive connection.
Rich
Well, hous wiring is different because it’s AC. There are really 2 phases with respect to the neutral, which then gets grounded at the box. That’s where you get the 240 from for a stove or electric dryer. With respect to neutral, each is 120V, with respect to each other, you then have 240V.
The decoder is more like an old car - nowdays pretty much all cars are negative ground, but in days past, many were positive ground. It also doesn’t help that in the US it is typical to use “ground” and “common” interchangeably - if it’s actually connected to ground, and not just a circuit common point, it’s otherwise referred to as “earth”. And traditionally, a schematic has placed the positive rail across the top and the negative, which is often shown using a ‘ground’ symbol, across the bottom.
As people discovered that there were more efficient ways to use transistors, especially for straight switching purposes, the open collector circuit was developed and this is what is used on decoders. Instead of switching the positive side on and off, you effectively crate a switch to ground. Because of the way transistors works, this is actually more efficient, which allows the same size transistor to handle more current - or a smaller transistor to be used for the same current. So each function “output” on a decode is actually a switch to ground, making the common wire the poositive side. An added advantage of this design is that you can connect and number of function wires to the same LED so that one LED is controlled by multiple functions, such that if any or all of them are on, the LED lights. You are simply connecting multiple switches to ground in parallel. Kind of like if you clip lead a light to a battery. One lead on each terminal and the light lights up. But you could put 4 leads on one side and it would still work exactly the same.
&nbs
[quote user=“rrinker”]
Well, hous wiring is different because it’s AC. There are really 2 phases with respect to the neutral, which then gets grounded at the box. That’s where you get the 240 from for a stove or electric dryer. With respect to neutral, each is 120V, with respect to each other, you then have 240V.
The decoder is more like an old car - nowdays pretty much all cars are negative ground, but in days past, many were positive ground. It also doesn’t help that in the US it is typical to use “ground” and “common” interchangeably - if it’s actually connected to ground, and not just a circuit common point, it’s otherwise referred to as “earth”. And traditionally, a schematic has placed the positive rail across the top and the negative, which is often shown using a ‘ground’ symbol, across the bottom.
As people discovered that there were more efficient ways to use transistors, especially for straight switching purposes, the open collector circuit was developed and this is what is used on decoders. Instead of switching the positive side on and off, you effectively crate a switch to ground. Because of the way transistors works, this is actually more efficient, which allows the same size transistor to handle more current - or a smaller transistor to be used for the same current. So each function “output” on a decode is actually a switch to ground, making the common wire the poositive side. An added advantage of this design is that you can connect and number of function wires to the same LED so that one LED is controlled by multiple functions, such that if any or all of them are on, the LED lights. You are simply connecting multiple switches to ground in parallel. Kind of like if you clip lead a light to a battery. One lead on each terminal and the light lights up. But you could put 4 leads on one side and it would still work exactly the same.
One of these days I really will put up some of these explanations on my web site, so I can just post a link instead of typing it every time.
–Randy
think about the car dome light for a moment. It goes on when any door is open. The switch at each door simply connects the the wire from the dome light to the frame which is connected to the negative battery terminal. The other side of the dome light is connected to battery (positive).
there’s no reason why you couldn’t run battery (+) to each door switch and the other side of the switch to the dome light. If one or more of the door switches was closed, power could be supplied to the dome light. But it’s less complicated and requires less wiring to only run one wire to each switch.
one big advantage of controlling something by connecting it to ground rather than power is that the controlling device doesn’t need to know what voltage is required. This allows the same device that simply grounds its input to be used with various devices that operate at different voltages.