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PIC 8-bit rapid prototype development boards...?

Discussion in 'Electronic Design' started by frenchy, Mar 5, 2008.

  1. frenchy

    frenchy Guest

    Howdy all,
    I recently took a class from Microchip learning to use their PIC24F 16-
    bit micros. I got the Explorer 16 development board and the ICD2 LE
    and got everything up and running with their MPLAB IDE v8.02 yadda,
    yadda. Everything is going very well, but I dont have any prior
    experience using more lowly 8-bit micros.

    A friend of mine wants me to design and build a little controller unit
    to put inside of his remote control boat that will receive some of the
    servo signals from a couple of different receiver channels and be able
    to fire some rockets and trigger various aquatic peripherals. This
    seems to me like I should look to an 8 or 14 pin 8-bit solution and
    that a 100-pin 16-bit processor would be significant overkill
    (understatement).

    I looked at the receiver servo signals on a scope and they are strange
    PWM type signals that vary in pulse width depending on what the
    transmitter/controller is doing (not sure if I should average them to
    DC and look at the DC level using an ADC or not). Anyway, it is my
    job to receive the various servo signals from the receiver and write a
    little program to have the micro control a couple of outputs to:

    a) light a fuse on a bottlerocket
    b) send out pulses to trigger a paintball firing mechanism (fully-
    automatic or semi-automatic or one-shot).
    c) perhaps a few other tricks.

    My question is this....
    1) Will my new ICD2 LE work with lowly 8-pin and 14-pin PIC 8-bit
    micros in addition to the PIC24F 16-bit micros?
    2) Although I have designed and build hundreds of my own PCBs in the
    past, this project doesnt really warrant a custom designed and built
    PCB...instead I would like to buy an "off the shelf" development board
    that will allow an 8-pin or 14-pin micro to be used to accept a couple
    of receiver servo pulse width inputs and actuate a couple of output
    transistor/driver circuits for US$20-40ish.

    Sure I could design my own PCB, but I would like to keep my actual
    design time limited to a couple of hours tinkering with the code
    instead of spinning a PCB, specing and ordering parts, etc.

    Any suggestions on quick deployment general purpose PIC development
    kits for such an application?
    I found this...
    http://www.talkingelectronics.com/projects/PIC_Lick-1/PicLick-1-P1.html
    It looks like the best so far for $30 or so with the PCB and all
    parts.

    I also saw this, but would require more tinkering for the output
    stages...
    http://www.microchipdirect.com/productsearch.aspx?Keywords=soic8ev
    http://www.microchipdirect.com/productsearch.aspx?Keywords=soic14ev

    Thx for any input.
    respectfully,
    frenchy
     
  2. donald

    donald Guest

    Welcome to the world of mocrocontrollers.
    Good idea.


    This may help:
    http://www.seattlerobotics.org/guide/servos.html

    There are many solutions to this problem.

    The micro counting the pulse width of at least two servos pulses,
    at the maximum of both pulses can trigger an output to trigger the "gun"
    Any vector plug board and point to point soldering.
    Good luck

    Please post some pics on your favorite pics site, or utube a video.

    donald
     
  3. You should measure the pulse width, which should be between 1000 and
    2000 usec, roughly.
    Yes, although you should probably stick with ones that allow you to
    dedicate the programming pins, so 16 or 18 pins might be more
    appropriate.
    Best regards,
    Spehro Pefhany
     
  4. nospam

    nospam Guest

    The ICD2 should program any PIC supporting ICSP. Many low end PICs don't
    have in circuit debug, or only have it special packages with extra pins
    used on ICD adapters.

    You would need to use a Microchip AC162053 adapter (about $35) to get ICD
    on a 16F628A design for example.

    If you want to write in C the device support offered by the limited free
    compilers bundled with MPLAB would also be a consideration.

    For a one/few off the cost difference between a low end PIC24 and a PIC16
    is trivial, you can get small ones in 28 pin DIL.
    --
     
  5. frenchy

    frenchy Guest

    Donald wrote: > This may help:http://www.seattlerobotics.org/guide/
    servos.html
    Frenchy responds: This did help, thank you!! We are using a Futaba
    set-up that looks very similar to that shown in the picture.
    Transmitter = Futaba FG series
    Receiver = FP-R7H


    Donald wrote: > The micro counting the pulse width of at least two
    servos pulses,
    Frenchy responds: When picking the micro (my first 8-bit project), if
    I want to count the pulse width of three servo intputs (for 3
    different output functions), does that mean that I need three separate
    8-bit timers? I am going to research the "counting width" method
    now. Thank you.

    thx,
    frenchy
     
  6. donald

    donald Guest

    As I stated earlier, there are many ways to do this.

    One way:

    Set an interrupt to trigger on 100 uSec interrupts.
    At each interrupt test the three bits and count a variable up if the bit
    is high, zero that variable if the bit is low.

    Outside the interrupt, test the three variables for a maximum value:
    2mSec / 100uSec = 20.

    Anything above say 18 is maximum. So two variables above 18 will set
    another variable, and trigger the "gun".


    On the remote control, pushing two axis to the maximum for only an
    instant, will trigger the "gun".

    Good luck

    donald
     
  7. frenchy

    frenchy Guest

    Aha, I thought those adapters were just to interface with that stupid
    proprietary phone jack....but now I see that they are for use with
    devices that dont have debug functionality built-in....very strange.


    Great advice! I guess since I already have the C30 compiler set-up
    and working, I should just get the lowest pin-count PIC24F that is
    supported by my compiler. I didnt realize they went down to 28-pin in
    a dip package. Nice. I just noticed, however, that they are all 2.0
    to 3.6vdc devices. I already have a 5vdc regulator in the system that
    I was going to tap onto for power. I guess I can add another 3.3v
    regulator running off from the existing 5v regulator (not too much
    wasted power to drain the batteries). The input Servo pulses coming
    from the Futaba receiver dont matter if they go above the 3.3v rail as
    long as I have 10k series resistors in-line to limit the injection
    current. Also, the output NPN transistors dont care if their bases
    are driven by 3.3v as long as the emitters are tied to GND and I have
    resistors in the base right?

    thx,
    frenchy
     
  8. frenchy

    frenchy Guest

    Donald,
    Thanks again for answering my elementary questions. Is there any
    advantage to using the input capture peripheral (Five 16-Bit Capture
    Inputs) when counting the length of these servo inputs?
    thx,
    frenchy
     
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