Connect with us

Laptop SPST

Discussion in 'Electronic Design' started by mpm, Oct 24, 2008.

Scroll to continue with content
  1. mpm

    mpm Guest

    What's the easiest, cheapest way to get a SPST switch capability out
    of a typical laptop computer these days?

    I need a control voltage to switch an external relay, and ideally, an
    input to confirm that the relay did in fact engage.

    Is there a USB or even a PCMCIA doo-hickey thing out there that can do
    this? My control software will probably be in VB, unless there's good
    reason to use something else.

    No idea is too stupid. :)

  2. Guest

    USB to serialport converter, use the control signals

  3. Rich Webb

    Rich Webb Guest

    Depends on what you've got, on the laptop and sitting around your
    workbench, but assumuning you're stuck with a modern USB-only setup, try
    an FTDI USB->232 cable. Control your relay with DTR or RTS and sense on
    DSR or CTS (or RI or DCD). (I'm assuming the VB Com Port driver can
    handle the handshake lines.)

    The DTR line should have enough umph to switch a transistor; certainly
    enough for a FET. What you'll need to do to get a state change on CTS
    depends on what's on the far end.

    The US232R-100 and -10 are available through resellers or from FTDI.
    Lots of clones, too.

    There are purpose-built USB gizmos that can do the whole thing for you,
    for a bit more money. I've used the ones from Measurement Computing for
    various projects. The USB-1208LS is reasonably priced, with A/D ports as
    well as digital I/O. You'd still need the tranny to drive the relay,
    though. The SwitchAndSense-8/8 uses a USB interface and has A/D and
    relays onboard. There's the CB-7063 and similar but you'd need RS-485.
  4. Guest

    Buy a mechanical SPST switch. Use the laptop as a stick to toggle the
    Stupid, or genius?
    You decide.
  5. mpm

    mpm Guest

    I stand corrected... :)

    These will be USB-only laptops (no legacy serial RS232).
  6. Rich Grise

    Rich Grise Guest

    By any chance, does your laptop have a serial port or parallel printer
    interface? You can directly manipulate the control/handshaking bits, so
    a SPST function, even with feedback, should be almost trivial.

    I'm not even going to hazard a guess if USB or PCMCIA are involved. ;-)

    Good Luck!
  7. Don McKenzie

    Don McKenzie Guest

    check out:


    Don McKenzie

    Site Map:
    E-Mail Contact Page: 1000's of electronic items
  8. Richard

    Richard Guest

    No parallel port either?

    Gee, progress happened, huh?
  9. Jasen Betts

    Jasen Betts Guest

    serial port, via USB if necessary, you get 5 inputs and 3 outputs each.

  10. Joerg

    Joerg Guest

    I've got this one. Not exactly cheap at around $100 but you'd have the
    feedback thing licked and VB should not be an issue either:

    Comes with a complimentary small edition of a factory automation
    software. Which is really easy to handle. Just if you want to have fancy
    looking buttons, and this stuff can more or less be mouse-clicked together.

    Check whether it has enough oomph to drive you load.
  11. Joerg

    Joerg Guest

    Yes, I absolutely like it. Simple, works, comes with oodles of SW and
    has a nice support forum. Once at a client I needed more channels so we
    bought a $5 USB splitter from Walmart and just kept stacking them.

    The only thing I don't like is its blood-red color. Oh well.
  12. Joerg

    Joerg Guest

    Supposedly people have automated whole garage-sized breweries with
    those. Can't really go wrong with a LabJack.

    If you do automate stuff with it always keep in mind that if the PC
    hangs so will (usually) the LabJack. So don't ditch any hardware
    shut-off techniques.

    Also, before you sink a lot of time into writing your own code and
    programs check out the DAQFactory software that comes with it. Not the
    full version but who knows, it might already do everything you want.
  13. Joerg

    Joerg Guest

    I don't know LabView Lite. DAQFActory is not geared towards research lab
    type jobs, it is all about factory automation. Basically SCADA:

    The nice thing is that their guys participate in a forum on the LabJack
    site. So when I found what I'd consider a bug someone got right on it.
    That impresses me a whole lot more than sales guys in dark suits ;-)
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day