Help Please. What are these symbols ?

Discussion in 'General Electronics Chat' started by HommerSimpson, Jun 16, 2012.

  1. HommerSimpson

    Thread Starter New Member

    Jun 9, 2011
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    What are these symbols. Im trying to make a logic Analyzer based on The Fabulous logic analyzer. And does It look like this MS paint drawing I did will work or need to add ? take away ? I have made a bubble tank for etching And i have all the stuff to make one. So With a little help. I might finally build something that actually works this time :} lol

    Thanks Greg
    [​IMG]

    [​IMG]
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    Those are the Output Enables.

    The name 'OEb' means "Output Enable bar". The "bar" refers to an overbar that would ideally be over the 'OE' indicating that it is active LO. This is also indicated by the bubble on the diagram. Active LO means that you take it to a low voltage in order to assert that pins function.

    If one of the OE pins is deasserted (by taking it HI), then the outputs controlled by it will be placed in high-impedance state and are essentially disconnected and floating.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    A small circle is a way to show the invert function.

    Pulling a drawing from my past.

    [​IMG]
     
  4. wmodavis

    Well-Known Member

    Oct 23, 2010
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    So from the schematic, since both of those OE inputs are connected to circuit common (or zero volt ref), both a & b outputs are continuously enabled and will reflect the same signal as on the inputs. The Inputs are continuously fed to the outputs and then to LPT-CONN J1 through the 1K resistors.
     
  5. HommerSimpson

    Thread Starter New Member

    Jun 9, 2011
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    well the schematic is just one i Used for reference this is the one im useing for layout of pcb.
    [​IMG]
    So.. do I leave pin 19 open ? Or should i put in a jumper there to connect and disconnect from ground ?

    And im drawing up another pcb.. make it smaller..
    So far I have only made one PCB that turned out ok but its not the design I want for the FLA software ^ that's the schematic I'm using to go by to draw up PCB .. IN mspaint.

    this is the one pcb i did manage to make. So I'm confident i can make another
    [​IMG]
    [​IMG]

    Thanks for all the help...
     
  6. HommerSimpson

    Thread Starter New Member

    Jun 9, 2011
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  7. HommerSimpson

    Thread Starter New Member

    Jun 9, 2011
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    uggg so i made A board and... I flipped pic horizontal but not vertical LOL oops
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    That is funny. But all you need for toner transfer is a mirror image, and for photographic a straight (no mirror image) is needed, though the image should be on the bottom of the transparency.

    I did pretty much the same thing (non mirror image) for my article How to make PCBs. Opps.

    There should be no horizontal or vertical involved, it can be one or the other.
     
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  9. WBahn

    Moderator

    Mar 31, 2012
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    That depends completely on what you are trying to achieve. Those pins are there for a reason. This is a bidirectional chip. Do you want to be able to send data in both direction? It has an output enable. Do you want to be able to put signals onto a bus that is being shared with other devices that also need to be able to put signals onto the the bus?

    The answers to those two questions determine how you hande the OEb and DIR pins.

    In general (and most especially for CMOS), never leave unused inputs floating. Pull them up or pull them down, but don't let them float. This goes for unused inputs in this buffer, too. So if you ever expect the possibility that any of the inputs of the buffers will be unconnected when the device is powered, put pullups or pulldowns on them.

    Now, your circuit seems a bit strange. It appears you are planning to hook this up to a Centronics parallel port. Is it supposed to take the place of a printer and you have a computer on the other end, or is your device going to take the place of the computer and drive the port? If the former, you've got a problem because the pins 2-9 are unidirection coming from the port and your schematic has the buffers configured to drive the port.
     
  10. HommerSimpson

    Thread Starter New Member

    Jun 9, 2011
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    http://tfla-01.berlios.de/ The Fabulous logic maker is what im trying to build. If that helps answer Your question about what im using it for
     
  11. HommerSimpson

    Thread Starter New Member

    Jun 9, 2011
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    Yes i figured out my mistake.. lol i had fliped it once.. then again.. was all bassakwards lol
     
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