Chris Fonville wrote:
>
> I should have been more specific, this is a neon speaker ring used to go
> around subwoofers in a car. It is powered from the 12V cigarette lighter.
> Unless it draws too many amps along side my other components, I should be
> able to use the yellow/black 12V lines on peripheral molex connectors (CD,
> hard drive, etc.) to wire the switch to the computer. The switch has Off,
> On, and Beat modes (Beat meaning it turns off and on with the music). So it
> seems like if it can turn off and on very fast I should be able to create an
> interesting effect cutting them off/on with hard drive activity. I am
> getting the feedback that I shouldn't use a mechanical relay, but either a
> solid-state relay, a transistor, or an optoisolator. I just need to find
> the voltage the motherboard puts out on the HDD activity headers and then
> where to buy the switch that I need. Thanks,
> Chris
>
> "Robert Baer" <> wrote in message
> news:...
> > Chris Fonville wrote:
> > >
> > > I have a neon light (12V) that I would like to blink with hard drive
> > > activity. I know I can't power it from the the HDD activity connectors
> on
> > > the motherboard, so how can I accomplish what I am wanting to do? Would
> I
> > > need to use a relay or transistor or something else? Should I be able
> to
> > > pick it up at my local Radioshack? Thanks in advance,
> > > Chris
> >
> > Neon light bulbs *cannot* work at 12V; the first useable ionization
> > potential of neon is about 65V (this is from memory; you are welcome to
> > look the value up in a Chem Rubber Handbook).
> > One could use the signal that normally drives the HD activity light,
> > which is normally a 5V logic level driving an LED.
> > Use a 10K resistor to drive the base of a high voltage (say 200V or
> > better rating) NPN; emitter to ground.
> > Use a 100K to 200K resistor in series with the neon bulb, to a 150V
> > supply.
> > This way, the 90V initial berakdown voltage is available, and the
> > current thru the neon is limited to prevent overheating and/or burnout.
> > How you get that 150V is another story.
Ahhh....
The mud settles in the pond.
The high voltage *is* available, and furthermore is independently
powered (in this case the car battery).
Unfortunately, you did not make it clear as to why a mechanical relay
could not be used.
I would guess that the supply for that light draws about one amp, and
maybe less.
If you desire a solid state solution, i would suggest the use of a
DMOS FET, because it is on and can easily be turned off. Choose one with
a low R(on) at one amp at a Vgs of zero volts.
The source is connected to the load and the drain to the battery.
Make sure that a resistor is permanently connected between the gate
and the source for static protection.
While even 10 megs would do the job, there is nothing wrong to use a
value as low as 10K.
The gate then could connect with HDD light logic level; every time the
HDD light goes on, then the license plate neon would go on.
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