LED and switch wiring

[jbaldwinroberts]

hey, i am making a light/fan controller at the moment but i have hit a problem. i have a normal switch with on and off and 2 connectors on the back. i am connecting one of these to 12 volts and the other to some cold cathodes with them connected to ground so that they will turn on if i put the switch on, but i want a 5v led to come on aswell when the cathodes are on. how could i incorporate this into the circuit. i have a drawn a little diagram in paint.

[IMG]

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thanks
- Joe

[xmastree]

Easy. Put a resistor in series with the LED. As for the value, assuming the LED needs about 10mA, and that the current resistor will give that from 12V, you need a resistor which will pass 10mA with 7V across it.
R=V/I so 7/.01 = 700 ohms. I'd use 680 ohms.

[jbaldwinroberts]

do you mean like this,
[IMG]

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Thanks

- Joe

[xmastree]

No, the LED and its resistor should go between the output of the switch and ground. Same as the inverter.

[jbaldwinroberts]

Ok, like this.
[IMG]

[/IMG]

thanks

-Joe

[xmastree]

The same thing (but mine's neater... :p )

[jbaldwinroberts]

Alright got it.

Thanks for the help +rep

-Joe