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Dual LED installation

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mike:
I purchased dual LEDs that have two leads that change the output from white to red when the +/- is swapped.  Given that I want to have them change on direction of the engine, but not fed from the motor output, how can I connect them without worrying that the two feeds from two different light outputs from the Rx will short them out or just not light?  I don't see where the light outputs are directionally connected, so you would have to manually push them for each direction, again this could cause both feeds to be on at once.

Cheers.  Mike

Alan:
The light outputs of an LM are effectively switches that make a connection to 0 volts (ground). You need polarity reversal i.e. 14V & 0V and then 0V & 14V. LM outputs can't natively do this.

You could use a resistor voltage divider between 14V and 0V to give you 7V connected to one side of the LED and then put a pull-up resistor on the LM output connected to the other side of the LED. The resistor math would have to be worked out.

When the LM output is ON (0V) current would flow through the LED in one direction. When the LM output is OFF (NC) current would flow through the pull-up resistor and the LED in the opposite direction. The LED would always be on but you could control its color with a button.

Resistor Voltage Divider example:


Pull-up Resistor example:

mike:
That would work for just the two dual LEDs, but I also intended to connect the forward three to go white in that direction and the rear three to be off at the top and the two dual LEDs to go from the white to red phase.  It would be very easy if I was using the rail power, but not so with the battery.  If there was a way to program two light outputs that required the other to be off first, then a manual transfer could be done.  I'm not against the manual mode, I just don't want to blow the LED by feeding it positive both ways at the same time.

I will take a look at how to convert your suggestion into the two circuits.  Thanks.

Alan:

--- Quote from: mike on December 12, 2018, 01:51:26 PM ---That would work for just the two dual LEDs, but I also intended to connect the forward three to go white in that direction and the rear three to be off at the top and the two dual LEDs to go from the white to red phase.

--- End quote ---

Same, same. The LEDs at each end would simply be wired in parallel, each with its own dropping resistor. [EDIT] Reread helped me better understand what you are saying. Still possible, circuit would be a bit more complicated.


--- Quote from: mike on December 12, 2018, 01:51:26 PM ---It would be very easy if I was using the rail power, but not so with the battery.

--- End quote ---

Doesn't matter. LM outputs are the same regardless of power supply type.


--- Quote from: mike on December 12, 2018, 01:51:26 PM ---If there was a way to program two light outputs that required the other to be off first, then a manual transfer could be done.

--- End quote ---

A simple SPST relay could do this - normally open relay contact fed with LM output #2, relay coil fed with LM output #1. Problem is finding a suitable relay sufficiently small enough to fit in the installation.


--- Quote from: mike on December 12, 2018, 01:51:26 PM ---I just don't want to blow the LED by feeding it positive both ways at the same time.

--- End quote ---

Won't damage LED. LED just won't light.

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