Re: Getting Parallel port to run relay

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Andy Wander <awander@v...>
wrote:

> Alan:
>
> I'm talking about the huge inductive "spike" that occurs when

the "control",

> whether it is a switch, a parallel port pin, or whatever, opens the

circuit.

> This causes a voltage spike that WILL fry transistors!
>
> But the OP has indicated that he DID have a suppression diode

installed

> across the coil, so that is probably not the problem.
>
>
> And it is very possible to control relays with the parallel port

directly;

> I'm controlling some small 5V relays directly with my parallel

port. You

> just nned to make sure that the relays source less current than the

port can

> sink(low-active is recommended).
>
>
>
> Andy Wander
> Verrex Corporation

Most of us who have made such a circuit drive a opto-isolator from
the parallal port, then a transistor from the opto and the transistor
can be a small 2n2222 or even a TIP120 or such.

But, the simplest way is to just use a SSR and save all the problems.

Just make sure the SSR is rated for the thing being driven. Most are
AC only or DC only. so, you cannot use a DC only to drive an AC
motor.

Dave