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Is it possible to make PC case lights only be on when the hard drive is read/writing?

I assume that you could make inner PC case lights only be on when the hd is reading/writing, by hooking up LEDs to the read/write LED on the front of my PC case. I will be using 10-20 LEDs, will that overload the circuit?

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frollard8 years ago
That will EASILY overload the circuit. The safest method: You need a transistor or FET to turn on and off your case lights, and switch the transistor with a device called an opto-isolator (or opto-coupler). It's an led and phototransistor glued together so that powering the internal led has no electrical connection to the 'switch' on the other side of the coupler. It's a way to keep the case lights circuit separate from the hdd led circuit so if something goes it doesnt wreck your motherboard. You need the transistor/fet because most optocouplers can only handle small amounts of current (not enough for 20 leds, but enough to handle the power transistor.)
Arbitror (author)  frollard8 years ago
Would you mind supplying me with a circuit diagram? -Thanks!
like this


You'd have to do some learnin' on how each part works, but its almost literally
plug the optoisolator into the hdd light (check polarity), then use the oi as a switch for the transistor. google how a transistor works, and it'll make perfect sense.
Arbitror (author)  frollard7 years ago
Wait- Do I even need a transistor? 'Cause if the opto-isolator only allows power when the LED is on, then wouldn't the string of LEDs only be on when the hdd read-write light be on?
Yes, but the optoisolator can handle TINY amounts of current, and a big string of leds can use into the full-amps range... thus, the opto switches the transistor, the transistor switches the leds.
Arbitror (author)  frollard7 years ago
Ok, got it.