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QTI Line Sensor Power — Parallax Forums

QTI Line Sensor Power

JondiceJondice Posts: 8
edited 2005-04-07 03:57 in Robotics
I have more experience with software than hardware, you might say I'm not grounded in electronics very well (haha ...). I was wondering if it would be possible to power several QTI Line Sensors with one I/O Pin - my problem is that I need separate readings for several sensors, but I can take them all at the same time. That way, instead of having 6 sensors using 12 I/O pins, I would be using somewhere between 7 I/O pins and 9 I/O pins. I don't know how much of a problem Fan-Out would be though ... any suggestions welcome, I just don't want to fry anything.

I'll have a pretty cool project to post when I'm finished, which for better or worse, has to be this weekend freaked.gif

Comments

  • JondiceJondice Posts: 8
    edited 2005-04-06 03:31
    Anyone know? I may go ahead and try it but I could be in some trouble if I break things.
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-04-06 04:17
    You might want to look at our line follower docs -- it uses a sensor like that on the QTI. If you combine that approach with an output expander (like a 74HC595) you could get to where you want to go.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas, TX· USA
  • JondiceJondice Posts: 8
    edited 2005-04-07 03:41
    Someone I know suggested using an NPN transistor and having the Collector set to Vdd (with the appropriate resistor in between) and the Base set to an I/O pin, then have all the of the PowerInputs for the QTI Sensors going to the emitter.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-07 03:57
    Jondice,

    ·· I would take Jon's advice.· That is not a typical configuration for an NPN transistor, and in fact, you don't want to connect the base directly to the I/O pin without a resistor·of at least 220 ohms.· Besides that, an NPN transistor, to put into laymans terms/simple terms, is meant to switch the negative side.· that is the Emitter is connected to ground, and the Collector between the device and Vdd.· A PNP transistor might be more appropriate to drive a positive load, however that would require a low on the Stamp pin, and you'd still need the resistor.

    ·· In any event, trying to simplify this is getting past the point.· Take Jon's advice and use an I/O expander.· there's plenty of code available for using them.



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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
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