Relays - help!

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ViperV990

Senior member
May 20, 2000
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Big electronic newb here... I'm looking for something that does the opposite of what a relay does, i.e. when supplied with current it cuts off the power to whatever it's connected to.

What I want to achieve: I want to have a single CCFL to replace both the power and HDD LEDs. It should be on by default and off whenever there's HDD activities. If an "anti relay" isn't what I'm supposed to be looking for, please point me to the right direction.

To think that I'm actually majoring in EE, this is kinda pathetic, lol... but yeah, I appreciate any help attempts.

Edit, I forgot to mention: It's best if the components I need is readily available in my local Radioshacks. Fry's is of course an option too.
 
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Zepper

Elite Member
May 1, 2001
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CCFL doesn't have the response time to act as a disk activity light - only LEDs do. Also I don't know how much current those front panel header pins are capable of supplying.
But I wouldn't think it could be much as the intended load is an LED. So you should probably be thinking solid state - latches, timers, one-shots, etc. to drive a relay.
. Power your CCFL via the "Normally Closed" contact pair of a SP-normally closed (or use the normally closed contacts of an SPDT) relay. Use the circuit to power the relay open on disk activity and include a resonable delay circuit so that the relay will stay off during a whole period of disk accesses rather than trying to flicker.
Probably be easier to think of some other idea for a disk activity signal... say 'latching' ON a string of "chasing" lights around the front panel or the outline of your window...
.b.h.
:sun: !
 
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ViperV990

Senior member
May 20, 2000
916
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I don't understand how or why CCFLs aren't fast enough. When I repeatedly power on and off the ones that I have I don't notice any slow down, delay or irresponsiveness. Mind explaining it a bit further? :)

Regarding whether or not the LED header will be able to power a relay - I never thought of that, thanks for noting it.

Oh and, I didn't know there were normally closed relays. That is what I was looking for, thanks.
 
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ViperV990

Senior member
May 20, 2000
916
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Alright, so I went to RS and got myself a 5V SPDT relay and hooked everything up. It turns out that the LED header indeed cannot drive the coil... but otherwise it's fine.

Well I guess I'll just have to look for a 3V or 2.5V SPST/SPDT relay...
 
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