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Controlling things with the parallel port

Discussion in 'Electronic Basics' started by joel, Aug 21, 2003.

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  1. joel

    joel Guest

    I have read a document on controlling led's with a parallel port. I
    plan on using the led's to make an optio isolator connected to a relay
    to control things around the house. first off, i was wondering if
    anyone knows of a book that covers things at a basic level like this
    and secondly a parallel port can only control 8 devices, is it cheaper
    to use multiple computers or is there perhaps some type of system out
    there that will let me control more?

    thanks for any input
  2. John Jardine

    John Jardine Guest

    You only need 1 computer.
    A method is to just use 3 of the port pins (eg D0-D1-D2), to -serially- send
    a set of on/off bits to one or more 74HC595 i.c.'s.
    Each 74HC595 chip can control 8 outputs. 4 chips (say) could control 32

    For example,
    D0 serially puts out the opto-led, ON or OFF bits to the 74HC595's
    D1 makes a clock pulse for each of these serial opto-led bits.
    After all the data bits are sent out then D2 is set high then low, to tell
    the chips to latch the sent data onto their output pins.
    (Use optos that have low current LEDs to avoid loading the 74HC595 o/p pins)
  3. the Wiz

    the Wiz Guest

    Check Jan Axelson's site and her book on interfacing the parallel

    It's relatively easy from DOS and Windows 3.x, but you need additional interface
    software (drivers, etc) for Windows 95 and higher.

    You might also consider a separate controller board, such as the one from (click on the Products link).

    More about me:
    VB3 source code:
    VB6 source code:
    VB6 - MySQL how to:
    My newest language - NSBasic for the Palm PDA:
    Drivers for Pablo graphics tablet and JamCam cameras:
    johnecarter atat mindspring dotdot com. Fix the obvious to reply by email.
  4. cpemma

    cpemma Guest

    The method John outlines has a circuit at DiscoLitez: and there's the software too.
  5. Si Ballenger

    Si Ballenger Guest

    I've got the below page showing how to use the parallel port to
    control my homemade webcam video switchers using "notepad"
    software. The "El Cheapo #3" setup could control ~40 things one
    at a time, and is made totally from Radio Shack parts. If you
    really want to be a parallel port control freak, the bottom link
    shows how to individually control up to 380 strings of christmas
    lights via the parallel port.
  6. Bob Masta

    Bob Masta Guest

    The parallel "port" includes 3 separate I/O ports: Data, Status, and
    Control. To control more than 8 bits, you can use the Control port
    to provide 3 additional bits directly (it's got special uses for some
    bits). For lots more outputs use those 3 extra bits as address bits
    to select one of 8 octal latches that are updated by the Data port.

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Shareware from Interstellar Research
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