Hello Guest it is June 16, 2019, 01:23:14 AM

Author Topic: switching  (Read 2763 times)

0 Members and 1 Guest are viewing this topic.

Offline stirling

*
  • *
  •  2,188 2,188
  • UK
    • View Profile
    • www.razordance.co.uk
switching
« on: September 08, 2010, 06:12:33 AM »
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
Re: switching
« Reply #1 on: September 08, 2010, 10:16:41 AM »
Quote
18V 10mA

cheapest way is transistor.
on-off

Amir
**Even a clock that does not work is right twice a day**

Online Tweakie.CNC

*
  • *
  •  7,808 7,808
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: switching
« Reply #2 on: September 08, 2010, 01:08:59 PM »
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.
« Last Edit: September 08, 2010, 01:11:50 PM by Tweakie.CNC »
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

*
  • *
  •  2,188 2,188
  • UK
    • View Profile
    • www.razordance.co.uk
Re: switching
« Reply #3 on: September 10, 2010, 04:07:15 AM »
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

Online Tweakie.CNC

*
  • *
  •  7,808 7,808
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: switching
« Reply #4 on: September 10, 2010, 04:26:40 AM »
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)  ;D

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: switching
« Reply #5 on: September 10, 2010, 10:24:12 AM »
Quote
logic level mosfets
Using them is not suitable for this issue.
you need only 10ma .you can build a simple circuit by transistor.

Amir
**Even a clock that does not work is right twice a day**

Offline stirling

*
  • *
  •  2,188 2,188
  • UK
    • View Profile
    • www.razordance.co.uk
Re: switching
« Reply #6 on: September 10, 2010, 12:03:31 PM »
I was suggesting them for Tweakie's laser not my trigger Amir. Keep up  ;D
Re: switching
« Reply #7 on: September 10, 2010, 12:47:59 PM »
sorry. my mistake
**Even a clock that does not work is right twice a day**