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Thread: Interface with a BioPac System

  1. #1
    Join Date
    Nov 2005

    Interface with a BioPac System

    [edited from a support email]

    We're trying to get MediaLab to interface with a biopac physiology
    system using a TTL out.

    They sent us to the following link for the cabling we need:


    But, $90 seems rather pricey.

    I thought I'd check with you to see if you thought that the parameter
    we've used to communicate with other systems using TTL-out:


    This should also work using any DB-25 Male and Female cable (which we can
    get for about $10 at CDW).
    Last edited by JEC; 11-07-2006 at 04:40 PM.

  2. #2
    Join Date
    Nov 2005
    It's been a while since I've spent time in the Biopac system, but here's
    what I remember:

    1. We do have many customers who have successfully made the interface.

    2. There was at one time an issue with the Biopac system not registering TTL input. We discovered that some newer computer systems (in particular, laptops) only output 3.3V on the parallel port, rather than the old standard of 5v.

    Thus, even when the MediaLab / DirectRT computer was connected properly to the Biopac interface, signals weren't properly recorded. This may have been resolved in the past few months.

    You can verify the output of your parallel port by sending data with our IOTester utility and measuring the output voltage with an oscilloscope or multimeter.

    Accessory parallel ports can be purchased from CompUSA or similar for $10 - $20.

    3. The pinout on the cable they're selling is different than the $10 CDW cable. Typically all 25 pins are connected straight through in a standard cable. This custom one has some pins swapped.

    However, it appears that it will work right out of the box. To save time, it may be a good option. If someone in your lab is handy with a soldering iron, however, the proper cable can be made for only a few dollars.

    4. For a basic MediaLab start/stop control setup, you just need to connect pin 2 of your MediaLab computer's parallel port to a TTL input on the biopac box and any one of parallel port pins 18-25 to ground on the biopac box.

    You might also check out this post


    for more details on sending TTL signals from DirectRT and MediaLab.

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