Red / Green Bi Colour LED wiring

[regme]

Hi

 

I'm trying to wire two Red/Green 3 pin LEDs so that one lights green and the other red and vis versa.  It's to indicate which way the point is set.

 

So I have joined the positive legss of both LED's together and the negative legs of the red and green together, so I gather they are in parrallel. (hope this is making sense)

 

I have 12v supply forward voltage is 2.2v and 30mA on the LED's so from the LED calculator I need a 180ohm resistor.

 

When I wire it up with the resitor the negative leg only the red lights up.  If I use two 180ohm resistors one for each of the negative legs then both the red and green light, which means that I'll need 4 resistors for each point.

 

I know I'm doing something wrong, I would have thought I would have only used two resistors on the negative side and at best one if I had it one the positive side.

 

Cheers

[RAF96]

Here is how I did it. Points to straight ahead gives a green on the main and a red on the branch and vice-versa. I also made up some traffic light indicators which sit beside each point rather than wire back to a mimic panel but the choice is yours.

 

http://www.rmweb.co.uk/community/uploads/1294780820/gallery_7193_1326_1962.gif

 

And

 

http://www.rmweb.co.uk/community/uploads/1294780820/gallery_7193_1326_7128.jpg

 

If however you want to show a yellow (i.e. red and green both on) to indicate say that a crossing loop pair of points are incorrectly set then you need to have separate resistors in each colour leg matched to the led characteristics as shown in the data sheet, i.e. forward voltage and current. This can take some time to achieve by experimentation with a variable resistor and a meter.

[dhjgreen]

I originally was going to use red/green LEDs but came down in favour of a mimic diagram.  Visiting operators do not look at it however, as it is the only one on our operating circuit, they just look at the points!

Edited January 12, 2018 by dhjgreen

[regme]

Hi

 

These LED's are on a mimic diagram, I did come across RAFHAAA96's idea to have the LED's track side but could source the LED holders.

 

This is how I have it wired at the moment, the blue is negative.

 

When I swap it around so the greens are together and the reds together they then light up WTF

 

Edited January 13, 2018 by regme

[John ks]

With a LED & resistor in series the voltage across the LED will remain constant & is determined by the characteristics of the LED

This voltage will differ for different colour LEDs

The LED won’t turn on if the voltage across it is lower then its rated voltage

With 2 LEDs in parallel the voltage across the 2 LEDs will be determined by the LED that turns on at the lower voltage, which means that there won’t be enough volts to turn on the LED with the higher voltage

 

Two ways I can see to fix your problem

1 Add extra resistors as shown on the left OR

2 Move the resistors as shown on the right, this is the equivalent to the link in RAFHAAA96’s post

 

 

You might find by increasing the resistor to 1000 ohm will still give good results

 

John

[RAF96]

Maplins CP52G was the 5mm red/green led c/w holder that I used. This is the data sheet from the Maplins product page for this led.

https://maplindownloads.s3-eu-west-1.amazonaws.com/CP52G-10780.pdf

I presume it still comes with the holder.

 

How to build the lamps is here

http://myweb.cytanet.com.cy/honnor/article5.html

 

Rob

[regme]

Thanks that worked a treat.  Now for more wiring and soldering

 

Cheers

[Steven B]

If you're only going to use one colour of each LED at a time then you just need one resistor per LED. Fit it to the common lead.

 

Steven B

[Ruston]

This topic came up in a google search and although it's not quite what I want, it seems a good place to start.

 

I have a bi-colour LED that I want to wire up but haven't a clue how as, unlike the above, it has only two pins. What I want it to do is to be wired with a sprung toggle switch that is always making a circuit one way but can be held to make a circuit the other way. The result being that the LED shows green all the time, except when the switch is pressed and it will turn red. I have no idea how to do this. Can someone help, please?

[AndyID]

2 hours ago, Ruston said:

This topic came up in a google search and although it's not quite what I want, it seems a good place to start.

 

I have a bi-colour LED that I want to wire up but haven't a clue how as, unlike the above, it has only two pins. What I want it to do is to be wired with a sprung toggle switch that is always making a circuit one way but can be held to make a circuit the other way. The result being that the LED shows green all the time, except when the switch is pressed and it will turn red. I have no idea how to do this. Can someone help, please?

 

You need a two-pole switch and you wire it up so that it reverses the current through the LED.

 

If that's not clear I'll post a diagram in a bit. (Still in bed here with first cup of coffee 😀)

[Ruston]

24 minutes ago, AndyID said:

 

You need a two-pole switch and you wire it up so that it reverses the current through the LED.

 

If that's not clear I'll post a diagram in a bit. (Still in bed here with first cup of coffee 😀)

Thanks. I realised that not long after posting. What I forgot to say is that one side of the switch is being used for something else but its sorted now by using two coloured LEDs.

[DCB]

It's very rare to find a heritage LEDs where red and green work with the same resistor.   The three pin ones need one resistor for green and one for red or the red is too bright and /or the green too dim.  Two pin one have the LEDs in inverse parallel so you need to reverse the polarity to change the colour,    Chances are it will also have built in resistors optimised for 12 volt but don't bank on it.

 

[AndyID]

54 minutes ago, DCB said:

It's very rare to find a heritage LEDs where red and green work with the same resistor.   The three pin ones need one resistor for green and one for red or the red is too bright and /or the green too dim.  Two pin one have the LEDs in inverse parallel so you need to reverse the polarity to change the colour,    Chances are it will also have built in resistors optimised for 12 volt but don't bank on it.

 

You can adjust the light outputs independently with a couple of diodes.

[DCB]

9 minutes ago, AndyID said:

You can adjust the light outputs independently with a couple of diodes.

 I don't understand.  Is that a typo?

[AndyID]

1 minute ago, DCB said:

 I don't understand.  Is that a typo?

 

Definitely not 😀. I'll post a sketch.

[AndyID]

Here you go