Re: Wiring LEDs to a DPST Switch

richhotrain <redking56@...>

--- In WiringForDCC@..., "Vollrath, Don" <dvollrath@...> wrote:

My mistake Rich.
For the RED LED, the cathode of the diode connects to the LED and the anode connects to the resistor and switch terminal. It is backwards in my description. But I think you have the resistor on the wrong side of the switch. It must be in the path to restrict current through both LEDs. It sounds like you are also trying to get them powered from DCC track power... Right? If so, there should be yet another diode to protect the LEDs from reverse voltage. I've put a connection drawing (worth a thousand words) in the files section. Look for RRampmeter LEDs.pdf Aug 29. It shows 2 diodes in series with the Red LED, just in case you have a high V green and low V red LED.
The Green LED will be on when it is safe to remove the RRrampmeter. Red when you are using it.

I reversed the direction of the two diodes and now the red LED lights with the DPST switch in the OFF position. When the switch is turned ON, the green LED lights up but the red LED stays on as well. But here is why that happens.

As I reviewed your drawing in the Files section, it reminded me of a question that you initially asked and I failed to respond to. Your drawing shows the RRampMeter connected to only one bus wire. However, I have set up the RRampMeter as a Panel Meter per the RRampMeter Application Notes to monitor the power supplied to the layout.

The two bus wires from the command station connect to one side of the DPST switch and the two bus wires leading to the track connect to the other side of the DPST switch. The RRampMeter is mounted on a panel and the alligator clips connect to the bus wires on either side of the DPST switch. With the DPST switch in the OFF position, current flows through the RRampMeter to the track. If the RRampMeter is removed from the panel to measure track voltage, the DPST switch is thrown to the ON position to provide power from the command station to the track.

Here is my wiring arrangement for the LEDs. The cathode side of each LED is soldered together and wired to the NO side of one switch pole (holding one bus wire from the command station). On the NC side of that same switch pole, a resistor is connected and wired to the green LED. On the NO side of the opposite pole, the Red LED is wired with a resistor coming off the switch followed in series by two diodes with cathode side facing the red LED.

As I study my own drawing of how I wired this arrangement, I can see why the red LED is always lit. Is there a way to keep this basic arrangement and have the red LED turn off when the DPST switch is flipped ON ?

Sorry for all of the trouble this is causing.


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