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Using the Parallax Position Controller and HB25 with a propeller — Parallax Forums

Using the Parallax Position Controller and HB25 with a propeller

jgundersonjgunderson Posts: 6
edited 2009-05-06 02:38 in Propeller 1
Hi,
Has anyone connected the propeller chip up with the position controller (Parallax part 29319)? I'm concerned because the position controller appears to have a 5 Volt data line, and the Propeller wants 3.3V If we were just reading data, we could use the same dodge as the Ping))) connection, and put a resistor in line, but we need to both send commands, and receive data.

So I thought I'd see if anyone else had already solved this.

Thanks in advance,
Jim

Comments

  • LeonLeon Posts: 7,620
    edited 2009-05-05 22:37
    Use a 74LVC4245.

    Leon

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  • jgundersonjgunderson Posts: 6
    edited 2009-05-05 23:00
    Leon said...
    Use a 74LVC4245.

    Leon

    Cool, Thanks, this is a much better solution than the one I was working towards.

    This chip looks like it requires a direction pin to be toggled between transmit and receive, so I guess I'll have to dedicate another pin on the propeller to handle direction. I don't suppose that you know of some auto-sensing version smile.gif

    Thanks again,
    Jim
  • hover1hover1 Posts: 1,929
    edited 2009-05-05 23:01
    Leon said...
    Use a 74LVC4245.

    Leon

    Leon spec'd a good chip. I am in the process of obtaining some converters from Sparkfun to do exactly what you are after:

    http://www.sparkfun.com/commerce/product_info.php?products_id=8745

    Regards,
    Jim
  • jgundersonjgunderson Posts: 6
    edited 2009-05-06 00:07
    hover1 said...
    Leon said...

    Use a 74LVC4245.

    Leon

    Leon spec'd a good chip. I am in the process of obtaining some converters from Sparkfun to do exactly what you are after:


    http://www.sparkfun.com/commerce/product_info.php?products_id=8745



    Regards,

    Jim

    Thanks Jim! We followed your link to the Spark Fun product, and thought we might get a road trip up to Boulder for a moment. However, it looks like they support up shift and down shift, but require separate lines in each direction. The Position Controller uses a single Tx/Rx line, so we would need to do some logic to multiplex. However, the schematic did inspire us to try a quick fix with a voltage divider and an inverter.

    Thanks for the help!
    Jim
  • Tom CTom C Posts: 461
    edited 2009-05-06 00:19
    Hi all,

    I am attaching a schematic of a circuit used by Steve Norris ( http://www.norrislabs.com/·) for·his RoboStool project.

    Steve has interfaced the Propeller to the the Position Controller with just a 1k series resistor.

    Just a thought.

    Regards,

    TCIII


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  • jgundersonjgunderson Posts: 6
    edited 2009-05-06 01:37
    Tom C said...
    Hi all,

    I am attaching a schematic of a circuit used by Steve Norris ( http://www.norrislabs.com/ ) for his RoboStool project.

    Steve has interfaced the Propeller to the the Position Controller with just a 1k series resistor.

    Just a thought.

    Regards,

    TCIII

    Tom,
    Thank you very much, this does work.

    I'm a little concerned on the Tx side - it seems that the 1K resistor should drop the 3.3V output of the Propeller chip to be very close to the logic threshold on the 5v TTL side. But it works fine on the test bench, so we will move it onto the robot and see how robust it is.

    Thanks to everyone!
    Jim
  • SeariderSearider Posts: 290
    edited 2009-05-06 02:38
    I am using the possition controller with the HB25 and the Prop and I·had no problem with just using a 1k resistor in series.

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    Searider
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