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Thread: TTL signal to biopac

  1. #1

    TTL signal to biopac

    I am trying to get medialab to send signals to biopac in order to note physiological responses after the presentation of certain stimuli. I have been looking at previous posts but I'm afraid they are too advanced for me. Can anyone provide a simpler explanation of the parameters I need to create? Is it possible that the communication between the two computers might not take place because we are using a laptop to run biopac?
    Any help would be greatly appreciated.

  2. #2
    Join Date
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    Quote Originally Posted by revezzzz View Post
    I am trying to get medialab to send signals to biopac in order to note physiological responses after the presentation of certain stimuli. I have been looking at previous posts but I'm afraid they are too advanced for me. Can anyone provide a simpler explanation of the parameters I need to create? Is it possible that the communication between the two computers might not take place because we are using a laptop to run biopac?
    Any help would be greatly appreciated.
    There have been some cases reported where a laptop's TTL output levels have been too low (3.3v) to work with external hardware. Most of the time, external hardware is expecting to see a 5.0v signal as a logic '1'.' Some laptops just don't send a strong enough signal to register.

    One of our users did post a sample MediaLab experiment which successfully interfaces with an eye-tracking system:

    http://www.empirisoft.com/support/showthread.php?t=152

    Can you post a link to the Biopac system you're using?

    Does anyone in your lab have access to an oscilloscope - or at the very least, a multimeter - that we could use for diagnosing the problem?
    John
    Last edited by JEC; 02-16-2009 at 03:09 PM.

  3. #3
    Hello,
    I'm not sure if the laptop problem applies to my situation because the computer with medialab is a desktop and the computer with Biopac is a laptop. Would the laptop have a problem picking up a stronger signal?
    Here is the link for the MP 36 system: http://www.biopac.com/Education.asp?Pid=4510. We are using the STP35A cable (http://www.biopac.com/Education.asp?Pid=4653&lower=1) to connect our desktop computer with medialab to our MP 36 unit.
    I am currently asking around to see if I can borrow an oscilliscope or multimeter from someone.
    Thanks!

  4. #4
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    Thanks.

    As best I can gather, your Biopac unit has 8 digital I/O pins available.

    Page 10 of this document

    http://www.biopac.com/Manuals/bsl%20...re%20guide.pdf

    Shows that Digital Input #1 of the IO port connector corresponds to Pin #10.

    The cable you're using shows that Pin 10 of the Biopac system is connected to Pin 2 of the parallel port:

    http://www.biopac.com/Education.asp?Pid=4653&lower=1

    Pin 2 of the parallel port corresponds to Bit 0 of an 8-bit data byte.

    http://beyondlogic.org/spp/parallel.htm

    I assume that you're hoping to send a signal from MediaLab to the Biopac system when specific pictures or stimuli are displayed on screen. Is that correct?

    Assuming it is, here's what you need to do.

    Note that I'm following the template shown here:

    http://empirisoft.com/support/showth...&highlight=TTL

    For a .5 second (500 mS) output pulse duration on Port 888 (0x378), the syntax is

    (d5<1,888,500>)

    This turns on only bit 0, which corresponds to a binary byte %00000001 or a decimal number 1. 'On' duration is 500 mS.

    Does that make sense?

    --------------

    Both DirectRT and MediaLab also come with a TTL testing utility called 'IOTest.' It can send and receive signals from the parallel port and is handy for testing. It's located in the 'utility' folder of each software installation.
    Last edited by JEC; 02-16-2009 at 09:23 PM.

  5. #5
    I finally got the I/O test to work today, but it is still not picking up a signal on Biopac. Would it be okay for me to email you a copy of my experiment so that you could make sure there are no small flaws that I am missing?

  6. #6
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    Quote Originally Posted by revezzzz View Post
    I finally got the I/O test to work today, but it is still not picking up a signal on Biopac. Would it be okay for me to email you a copy of my experiment so that you could make sure there are no small flaws that I am missing?
    Sure, that's no problem. Just sent it to 'sales' at this domain.com.

    However, you should be able to use the IO test utility to communicate with Biopac. So if that's not working, we're still missing something re: connections or syntax.

  7. #7
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    Nov 2005
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    294
    UPDATE:

    We learned that the laptop running MediaLab had a parallel port not 'strong' enough to drive the BioPac box. So we switched to a desktop computer and had good luck communicating between Empirisoft's IOTest utility and the Biopac system.

    After further testing and removal of a small typo in the experiment file, we were rewarded with a properly running MediaLab experiment which triggered the Biopac system at the appropriate time.

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