It looks to me like you wish to switch an (isolated) external current loop.
If you are using a current loop because long lines make voltage sensing
chancy why don't you follow the tried-and-true method used by RS232?  Kick
the voltage up on the comm connection and slow the signaling rate until
comms become reliable.

Or if it is truly low current (and you can afford loosing a little voltage
in your current loop) why not use a 4066 quad analog switch chip?

Isolation, 4 switches per package, works at 5V and cheap!

Bye.

-----Original Message-----
From: Nick Veys [mailto:nick@VEYS.COM]
Sent: Friday, 3 August 2001 4:19
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: Solid state relay difficulty


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


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Roman Black
> Sent: Thursday, August 02, 2001 12:48 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Solid state relay difficulty
>
>
> Nick Veys wrote:
> >
> > Hmm, I don't know what you mean, like braking in a car?  If
> so, no.
> > All it's doing is shorting two leads to turn a device on,
> just needs
> > to be momentary and logic level driveable.
>
>
> Hi Nick, this shouldn't be too hard!
> What type of device? Is this switching AC mains?
> -Roman
>
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