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Question about repurposing pins on the prop boe. — Parallax Forums

Question about repurposing pins on the prop boe.

undermuttundermutt Posts: 22
edited 2013-12-11 11:09 in Propeller 1
On the prop boe pins 20 and 21 are dedicated to the microphone. I would really like to use those pins for something else, like the xbee.

Is this possible without trashing the boe?

Thanks,

Rick.

Comments

  • PublisonPublison Posts: 12,366
    edited 2013-12-04 13:06
    undermutt wrote: »
    On the prop boe pins 20 and 21 are dedicated to the microphone. I would really like to use those pins for something else, like the xbee.

    Is this possible without trashing the boe?

    Thanks,

    Rick.

    Doubtful to get a good signal in or out with all the passive components in the circuit. (Someone will make me a lier) :)
  • undermuttundermutt Posts: 22
    edited 2013-12-05 05:47
    Nothing against you but I hope so. I would reallllllllllllllllllllly like to reuse those pins for something else.
  • Mike GreenMike Green Posts: 23,101
    edited 2013-12-05 07:18
    It all depends on that "something else". You've essentially got the two pins connected via a 100K resistor and there's a substantial (1000pF) capacitor connected to Vcc and ground. That's going to limit the rate of change of any applied signal, In addition, you've still got the microphone connected via a capacitor. A loud clap might couple a pulse through that would upset whatever you're doing.

    For sure, you could attach a low impedance load like some LEDs with their resistors to those pins. You could also attach some switches to those pins as long as you kept their resistors low in value, maybe 4.7K or 3.3K.
  • undermuttundermutt Posts: 22
    edited 2013-12-10 10:41
    Mike,

    Thanks for the info. I may get back to you for more if I decide I need to use them. My idea was to hijack the pins before they made it to all of that extraneous stuff and use them for the xbee wifi.

    Rick.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-12-10 10:54
    There may be ways to share pins. If you list the devices you plan to connect to the PropBOE, someone might have an idea of how to share some of the pins.

    I'm pretty sure I've seen forum members share SPI and I2C clock lines. TonyP can control a '595 chip with a single I/O pin (I think it involves the use of chicken entrails (as in Voodoo)).

    Someone might see ways to share pins you hadn't considered.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2013-12-10 15:59
    I was going to suggest desoldering components but looking at the cost of the BOE ($129.99) maybe that isn't the best option.

    I wonder if another option might be to look at one of the much cheaper propeller boards - eg the propeller mini for $24.99. Then you have much more control over the pins as you can decide what they are connected to.

    There are lots of other boards also on this page http://www.parallax.com/catalog/microcontrollers/propeller/boards - maybe one of those has the components you need and also enough spare pins for your own uses?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-12-10 16:19
    Dr_Acula wrote: »
    I wonder if another option might be to look at one of the much cheaper propeller boards - eg the propeller mini for $24.99.

    Good idea except for the Propeller Mini example. I don't think the Mini has all the I/O pins broken out.

    My new favorite Propeller board (since the QuickStart's price was raised) is the Propeller Project Board since it's $25 and has a nice switching regulator. It also has a place to add a SD card, and VGA connector. I even like the surface mount area (I didn't the first time I saw it).

    Edit: Thanks to Dr_Acula's link, I see the Project Board is currently on sale for $22.49. Now that's a great price. If you get a Project Board you might want to get the uSD card holder to go with it. I also just noticed the Activity Board is deal of the day.
  • undermuttundermutt Posts: 22
    edited 2013-12-11 11:09
    Thanks for the suggestions.
    I am very far from an electronics person which is why I chose the prop boe. It had alot of the stuff I wanted already there.

    Learning spin and parallel processing is enough of a brain drain at this point in the project. If I find, after getting the basics done, that I really need those extra pins I may tackle one of the other boards and add my stuff to it. We shall see.
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