Hi Nick,

At 1:19 PM -0500 8/2/01, Nick Veys wrote:
>I know it should be hard, hence my difficulty! :)  Go figure!
>
>It's simply shorting two pins on a little fan controller I have made
>here, on the device it brings +5 to Ground to let it know to turn on

        If this is the case why not use a NPN transistor. Connect the
control line through a limiting resistor to the base, emitter to
ground and the pin to be switched to the collector ?


>but
>really, I don't want it to matter... I simple want something that will
>be switchable from: Open circuit -> Closed circuit -> Open circuit in
>1/2 a second or so, nothing complex, nothing elaborate, simply like what
>a relay would do, only no real significant current (uA) or anything will
>flow though this so it doesn't need to be heavy duty at all!
>
>I'm looking at some Optoisolators

        These are only necessary if you want to electrically isolate
the control line from the controlled circuit.

>and some seem like they might work,
>and I really like the idea of having 4 channels,


        Multiple transistors can be had in a multi-pin DIP package,
or since your switching 5v to gnd, with little current, you could use
CMOS switches (a.k.a. transmission gates) such as the 4066, 4
switches/package. This may be a better choice since the inputs are
logic compatible, so the limiting resistors can be eliminated.

>that would simplify my
>PCB...  But again I have no experience with those and don't know if they
>would work either...
>
>nick@veys.com | www.veys.com/nick
>

Heinz

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