Electrical Voltage Question

[TheMainMan]

I'm not sure how to do this so I'll put this out there to anyone with more electrical knowledge than I have. I want to wire an led up inside my DVD drive so that it only comes on when the tray is open. There is a switch that allows the drive to know whether the tray is open or not however the switch only puts out 3.25V. I have resistors for 12V that make the LEDs bright enough but don't know how to wire it up so that the switch will turn it on and off.

At this point I'm probably going to have to get a roller switch and mount it at the back so that the tray closes the switch.

[mDust]

Depending on the LEDs, 3.25v should be fine without any resistors.
What LEDs do you have?

[TheMainMan]

They are rated for 1.8V-2.2V. When I hooked it up directly with no resistor the LED was pretty dim. I know the connection was definitely providing 3.25V as I tested it with a multimeter.

[mDust]

They are rated for 1.8V-2.2V. When I hooked it up directly with no resistor the LED was pretty dim. I know the connection was definitely providing 3.25V as I tested it with a multimeter.

I'm not sure why it would be dim, but try hooking up two of them in series. That should work without a resistor.

If you want to put a resistor in to use only one LED, you can use this (http://led.linear1.org/1led.wiz)calculator to figure out a proper resistor.

Depending on what you're trying to do, I'd add the 2nd LED so at least you get something useful out of the power used instead of just waste heat.

[slaveofconvention]

I'm NOT an expert but there's more to electricity than just voltage - is it possible the switch just doesn't supply enough current to light up the LED properly? If that's the case then you could probably rig up a pretty simple circuit using a relay to switch a more powerful source on and off for the LEDs, using the switch as the relay trigger

[mDust]

I'm NOT an expert but there's more to electricity than just voltage - is it possible the switch just doesn't supply enough current to light up the LED properly? If that's the case then you could probably rig up a pretty simple circuit using a relay to switch a more powerful source on and off for the LEDs, using the switch as the relay trigger

If the source of power is the PSU, I'm not sure why there wouldn't be enough current. LEDs only need around 5-20mA to light properly.

And since the LED has been reported as less bright with more power, I'm fairly confused. I'm not an expert on any subject, but I thought I had a basic understanding of Ohm's Law. Everything I thought I knew is either wrong or LEDs have quirks that I'm not aware of.

[TheMainMan]

The source of the power is the Tray Out pin and a ground on the front circuit board of a dvd drive. I tested the voltage but didn't think to check the current. I'll have to try that tomorrow.

As for setting up a relay, I have no idea how to go about doing that so any help in that area would be greatly appreciated.

Thanks to everyone for the feedback.

[xr4man]

i don't think you'll be able to check the current without an adjustable load. you have to put your meter in series to check current, unlike voltage that you put the probes in parallel.