RailPro > RailPro Specific Help & Discussion

Control Bi-Colour LEDs

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Gibs:
Three leg LEDs come in two types. Common positive ( the type you want) and common negative. Just check which type you have before soldering up all the connections. If wrong type they can be found on places like Amazon or AliExpress cheap as chips with leads attached in 3,5 and 10mm clear LEDs.

Gino:
I spoke too soon. After drawing out the circuit I found out that the LEDs used are common cathode. So the circuit will not work using the +5V supply through the LEDs and to the output.

Gibs you are correct. You need common anode LEDs to make things work.

I have another thought.
Can you use the output to supply power through the LEDs and connect them to the Common pin?
Can this work using an LM-4S-G? If so then I could use the existing common cathode LEDs.

Gibs:
What a lot of people tend to forget is what we term as "OutPuts" on RP's LM's are in fact Negative switched connections. The "Common" which by normal conventions would be a common "Ground/Negative" is in fact the "Positive" power supplied connection.

So you need a Common Positive LED to do what you're after.
The correct "Colour" resistor needs to be on the switched Negative connections or the LED wont work correctly.

Now as to your idea, I have no idea as to what voltage and polarity is available at the "common" connection on the LM 4G, its not displayed on the diagram so I'd need to know that before I'd even think about give you a yes or no, but even if its/was usable, you cant control it like the output connections that are for lights/effects as far as I can tell.

Gino:
I asked Ring Engineering if the output(s) of the LM-4S-G could be the source to power the LEDs. The answer was NO. The outputs can only sink current.

So to make things work I went ahead and purchased some common anode bi-colour LEDs.
I will replace the ones on the boards and wire them accordingly.

Thanks for all your comments and suggestions.

Gino

gregeusa:
Gino, I have a large number of USAT locos, what model do you have that has a 3 lead red/green led?

Mine are all bipolar, 2 lead.... perhaps you bought them used and someone changed the LEDs

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