At 04:03 PM 12/22/2003 -0600, you wrote:
>I was wondering about driving a relay with a pic,
>and then I began to wonder how solid state relays
>are driven?

The type that say 3-32VDC in can generally be driven
directly from a PIC. I've never seen one that is not
galvanically isolated, though very old ones used reed
relays or magnetics rather than optos.

There are also ones that will switch DC, but they are
different parts and have to be ordered as such.

>Are they opto-isolated things that can be turned on
>and off with the pics pins?
>
>If not, is there anything that can be used directly
>on the pics pin to turn on and off house current type things
>or even 12 vdc and 1 or two amps.
>
>One project is a 12 vdc solenoid valve, and the other is a
>high amp element in a water boiler.

You need a LOT of heat sinking for high amp switching.
As a first approximation, think of 1W per A. A 50A element
will require a BIG heatsink. Keep in mind that semiconductors
typically fail ON and try to avoid getting killed in ensuing explosions
etc.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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