Need some wiring help

[matta757]

Hey guys,

For those of you who have good knowledge of electrical circuits (mine is only so-so) I need some guidance. I am rewiring my overhead panel and I want to use an old PSU from a computer to power my LED lights inside my Korry switches. For some background, I have been using several of the +5v outputs on my BUO836X cards to power the LED when the Korry switch is closed. So what I had was the LED with the cathode end wired to the 5v output and the anode end wired to the switch, so that when the switch is activated, it closed the circuit and illuminated the LED.

Now that I have backlit panels that will use the PSU for power, I wanted to use the 3.3v output from the PSU to power the Korry LEDs. I was thinking it would be a simple switch of the voltage wire from the BUO836X card the PSU output connected to the cathode end, but this has not been the case. I know (or at least think I do) that there is something awry with the GND on the PSU. And everytime I connect the GND wire in the circuit, the LED lights up regardless of the status of the switch. Please see diagram.

https://www.flickr.com/photos/matta757/15107862501
(Sorry, I can't get the image to show without the link)

Does anyone know what I am doing wrong here and/or if this will work with the PSU as the power supply for the Korry LEDs?

If you need more info that I failed to provide, please let me know.

Thanks,
Matt

[Nat Crea]

Ouch...wont work.
Your BUO836X and power supply are independent and have separate earths,
which means you cant complete the "circuit" in your second diagram.

I cant say for sure, or what type, but may you could add a resistor in-between the LED
and the 5v output of the BUO836X to lower the voltage.

Nat

[KyleH]

If your switch is a dual pole, you could wire the LED with the 3.3V output through the other pole. Otherwise you will have to use the power from the card. Don't forget current limiting resistors or your LED's will burn out.

[matta757]

Thanks guys.

Matt