Logic Relay Card

Discussion in 'The Projects Forum' started by Plecc, Jul 1, 2011.

  1. Plecc

    Thread Starter New Member

    Aug 26, 2010
    22
    0
    Hi all,

    I'm attempting to build a hobby CNC router in my spare time,
    And would like to try and make my own relay card.
    I need to be able to switch 3x 240v 13A outputs to drive the spindle, vacuum and a light, all driven via the parallel port.
    I have built my own PCB's quite a lot, but always from kits or someone else's plans and ideas. I don't really have the knowledge to create circuits from scratch myself.

    But i know you guys do!

    If anyone knows of a good schematic or has the patients to help me out please let me know.:)

    Thanks.
     
  2. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    hi,
    what is this CNC??
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Bill Bowden has some example schematics and code on his site:
    http://www.bowdenshobbycircuits.info/page6.htm#PPRIC

    If you are running later versions of Windows, the OS won't like you trying to use an applications program to take control of the printer port.

    You would really be far better off buying a kit with relays already provided rated for mains power, and controlled via USB instead of the parallel port.
     
  4. Plecc

    Thread Starter New Member

    Aug 26, 2010
    22
    0
    Thanks for the replies,

    RRITESH KAKKAR,
    CNC stand s for Computer Numerical Control,
    basically a machine tool or robot controlled by a PC.

    SgtWookie,
    Thx allot, great info.
    I'm using an old dell IBM PC running xp, fairly sure it puts out traditional 5v logic.
    Your right about the usb option, but Mach3 my control software only supports the parallel port.
    I like the took of the 12v circuits, now just to be awkward.
    would it be simple to add an LED to show when the relay is live,
    and an opto-isolator between the port and circuit?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Funny that you apparently didn't like the SSR option, as that effectively IS an optoisolator as well as a solid state relay! You get rid of the clacking of electromechanical relays, as well.

    Perhaps you should take another look at that option? You can get SSRs with higher ratings than the one Bill suggested in that circuit.
     
  6. Plecc

    Thread Starter New Member

    Aug 26, 2010
    22
    0
    Thx SgtWookie,

    So it is, i didn't notice that!
    can it really be that simple?
    The main reason i went for the 12v options was because i thought it would be easier to power from my 24v power supply using a voltage regulator.
    But i could supply the 5v circuit with power from USB but I'm not sure if this is a good idea or if USB even has the current to switch the relays?
    Guess i could step down 24v to 5v using two regulators!
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Your Dell PC has a variety of voltages available, but +5v, +12v and GND are arguably the easiest to access. Just get one of those Molex wye power connector splitters. Red to black is 5v, yellow to black is 12v (black is ground). Using a splitter means that you won't lose a connector inside the PC, and also you won't have to cut your power supply's harness; just plug in the wye.
     
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