Actually, I use a DPDT switch to control a Tortoise Switch machine and a bicolor LED (bipolar) to indicate the position of the turnout. The LED is pluged on a separate source and controlled by one of the internal DPDT of the Tortoise (simple wiring).
I am repositionning the DPDT a lot farther from the Tortoise and I would prefer not to have to run long wires from the Tortoise to the LED which will be located near the DPDT on the main console.
- Can I wire the LED on one of the wires that go from the DPDT to the Tortoise?
- How can it be done?
- Will I need a resistor?
- Will this impare the way the Tortoise will function?
Those questions might seem basic to some of you but when it comes to wiring I am frequently lost.
Guy
Modeling CNR in the 50's
You need the 2-lead bicolor LEDs, and then it can be done. Yes, it just goes in line with the lead from the DPDT to the Tortoise motor. You do not need a resistor, the Tortoise motor draw about 15ma which is a safe value for LEDs. It does reduce the voltage to the Tortoise by the LED rating, usually 2.8-3V. With a 12V supply this means about 9V to the Tortoise, which is actually better than the fill 12V - it's quieter by a lot, yet still has more than enough power.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I mount DPDT toggle switches on control panels and solder bi-polar LEDs to the center tabs on the DPDT as Randy suggested. I always use a resistor on one leg of each LED.
Rich
Alton Junction
That's if you put it across the motor wires - then you need a resistor, and it will not affect the Tortoise. You cna put them in series with the Tortoise motor and it doesn't need a resistor.
Parallel to Tortoise: resistor needed
series with Tortoise: no resistor needed
Go back and read the LION's primer on Tortoise machines.And get rid of the DPDT machines. Run the Tortoise, and ALL of the LEDs and any auxiliary relays that you like all with ONE WIRE!
The LION and the Tortoise
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
rrinker That's if you put it across the motor wires - then you need a resistor, and it will not affect the Tortoise. You cna put them in series with the Tortoise motor and it doesn't need a resistor. Parallel to Tortoise: resistor needed series with Tortoise: no resistor needed --Randy
Back to the basics - another fundamental electrical law like Ohm's Law. Kichoff's Laws are for series and parallel circuits. It explains why Ohm's Law works to calculate a resistor to use with an LED, among other things.
Series law: Loads in series each get the same current. Voltages add.
so a Toroise that draws 15ma, anything in series with said Tortoise will ALSO get 15ma. No more, no less. And if you feed the combination with 12V, and the LED has a forward voltage of 3V, the Tortoise gets what's left over, or 9V.
Parallel law: Load in parallel get the same voltage, currents add.
So two Tortoises in parallel will draw 30ma fromt he power supply (15ma x 2). Or 100 Tortoises, 1.5 amps. (100 x.015a each). An LED in parallel with a Tortoise, fed by a 12V power supply, gets 12 volts.
These laws also explain the behavior of a series LED and Tortoise - when stalled, the LED is fairly bright (or nuclear in the case of those ones Farella just got), but when the Tortoise is moving between sides, the LED is dim. The Toirtose draws a lot less current when it is moving, compared to the 15ma at stall. Lower current in the Tortoise = lower current through the LED. Since LEDs work on current and not voltage, the more current, the brighter. The less current, the dimmer.
Now, we want the LED to run at 10ma. It gets 12V, and we know it has a forward voltage of 3V. We know we are going to add a resistor in series with the LED. So we now have the information we need to use Ohm's law, because of Kirchoff's laws. If the LED takes 3V of the 12V, the resistor will get 9V of it. And if we want 10ma throught he LED, the resistor in series will also get 10ma. Now we have the E (voltage) for Ohm's law at 9V, and the I (current) at 10ma. Solve for the unknown (R) to get the resistence value, in this case 900 ohms. (E=IR, or R=E/I. R=9/.010).
See - this isn't really hard. When you get beyond basic resistors and diodes it can, but while knowing how to wire LEDs for indicators and structure lighting is useful to most any modeler, knowing how to design transistor throttles and so forth is not.
Tanks everyone.
I now have a better understanding on how to use serie and parallel wiring to suit my needs.
Randy,
Your explanations are always simple and informative. Just right for the newbie in electronics.
Lion,
Your site is very informative and taught me some new ways to wire a layout. Your wiring is impressive.
In the following thread (google searched) there is a wiring diagram someone included along these lines:
http://cs.trains.com/mrr/f/744/t/243219.aspx
Paul
Modeling HO with a transition era UP bent
Thank you everyone. Here are the results. First, two green LEDs wired in serie betwee the DPDT Switch and the Tortoise to indicate which track is open.
Second, the switch second from the left controls the exit of the reverse loop. The green LED is a bicolor that indicate the polarity of the loop, green for normal, red for reverse
That forum is very helpful.