I need to switch 18V 10mA via TTL (turn on/off a plasma torch via the parallel port).

A relay seems a bit overkill for this - doesn't it? and I read somewhere (I think) that such low current is not best switched by a SSR - true? or have I made that up?

Thoughts on cheapest/bestest/nicest/properest way to do this?

Cheers

Ian

18V 10mA

cheapest way is transistor.
on-off

Amir

Ian,

The common SSR's need to switch a/c loads as they require the zero crossing point for switching off but having said that I switch my cross hair pointer on / off with a mains connected SSR which powers the wall wart to output the 5Vdc for the pointer. The SSR, which has internal opto isolation, is powered directly from the LPT port.

Tweakie.

OK guys - thanks.

Tweakie - have you looked at logic level mosfets for your cross hair pointer - they sound like the mut's nuts for that.

Ian

Thanks Ian but I needed -5volts (relative to the frame) because the body of the pointer is connected to + so it was easier, for me at the time, to get the required negative voltage from a wall wart.
Yes I agree that these logic level switching MOSFET's would be brilliant for a lot of applications. (more circuit board routing is on the cards) 

Tweakie.

logic level mosfets

Using them is not suitable for this issue.
you need only 10ma .you can build a simple circuit by transistor.

Amir

I was suggesting them for Tweakie's laser not my trigger Amir. Keep up 

sorry. my mistake