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Need small micro dev kit

Discussion in 'Electronic Design' started by Yzordderrex, Nov 14, 2006.

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  1. Yzordderrex

    Yzordderrex Guest

    The text below was part of an ongoing thread that I was participating
    on another board. Some of the members on the other board asked exactly
    what I was wishing to accomplish so the topic is treated in more detail
    than most. I'm still looking for a small (INEXPENSIVE) kit

    I want to develop an inverter to take a 200v dc bus and convert it to
    120vac. I will use 4 mosfets configured in an H configuration. By
    controlling the switching trajectory of each fet the output will be
    sinusoidal in shape. Of course there will be some switching garbage in
    the
    way of harmonics that I will have to deal with. A mosfet will allow a
    carrier switching rate of say 20kHz no problem - the faster you switch
    the
    higher will be the spectrum of harmonic trash that needs to be
    filtered. So
    then the faster you switch the easier the filter design becomes. A
    switching
    rate that is an exact multiple of 60Hz would be good so that the
    carrier and
    the fundamental components can be synchronized - called synchronous
    pwm.
    This may be easier to implement with a small micro.

    The 200v dc bus will probably come from 4 car batteries connected in
    series.
    This will go into a full bridge phase shift converter running at 100kHz
    or
    so - I've got a couple kicking around here that I have already built.
    The
    200v bus can be regulated to within a gnat's ass, so the sinewave
    inverter
    can run open loop without having to compensate for bus voltage
    variations.

    So what the micro has to do is output the pwm routine to drive the 4
    mosfets. This could be as simple as a counter and a table with the pwm
    times stored. Go to address 1 and load that number into the
    counters(and
    the info for state latch as well). Count down to zero and go to address
    2
    and load that number into the counters. Perhaps there are 200 (for a
    12kHz
    carrier) address that store the timing and state information for one
    sinewave.

    There are only 4 possible states with the inverter while it is
    running.. Top
    right and bottom left both on. Top left and bottom right both on. Both
    top
    on, or both bottom on - each called a zero state. Only other possible
    state
    is all fets off, but that is never used while the inverter is running.
    Never are the top and bottom transistors in the same pole on, because
    that
    would put a direct short across the bus.

    My microprocessor skills are almost non-existant so I am looking to
    getting
    my feet wet. Whatever platform I choose (based on you guy's input) it
    should be above everything else easy to learn. It must also have the
    computing power necessary to do the pwm routine. I'm basically looking
    for
    somebody to tell me to go to digikey and order such and such a kit.

    thanks
    Bob
     
  2. Hmmmmm.....
    sounds like a DarwinAwards project, go for it...


    martin
     
  3. Eeyore

    Eeyore Guest

    To ensure accurate timing it's best to 'flip' each state change with an
    interrupt driven by an on-board timer.

    Sure but you also need to consider turn-off time - the fets don't stop
    conduction instantaneously so you need some 'dead-time' when switching between
    states. Some mosfet driver chips do this automatically for you btw.

    It's very do-able.

    I'd actually be tempted to do it with a look-up table that stores the switch on
    and off states and increment the index with a timer.

    Graham
     
  4. AndyS

    AndyS Guest

    Andy writes:
    I like the PIC 16F84 . It is cheap, has a 20mhz clock, and
    draws
    about 5 mils --- costs about 5 bucks... Has on-board EEprom
    memory and versatile built-in I/O . I've used it in several ham
    projects...


    Lots of PIC versions are available, and there are development
    kits and programmers for sale very cheap.
    Many have built-in A/D converters.

    Also, a BASIC compiler is available....

    It isn't the fanciest one, but for one-chip applications it does a
    fine job. Just google up some info on it and plan to spend a
    week or so learning to program it. It has a simple machine
    instruction set. And a simple BASIC instruction set for the
    BASIC compiler.....

    Good Luck,
    Andy W4OAH
     
  5. Guest

    Since when are car batteries 50V?
     
  6. Eeyore

    Eeyore Guest

    He did explain he was using a step-up arrangement.

    Graham
     

  7. New cars are supposed to be built with 42 volt batteries before
    long. The charging voltage would be about 48 volts.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  8. Yzordderrex

    Yzordderrex Guest

    Good point on the 48v charging system there Mike. I'll probably need
    an alternator someday. This system could actually make a nice standby
    power system to keep the furnace & radios running when power goes out.

    Sorry, I forgot to mention that I am a power EE. I design large
    inverters for a living. I've got a handle on the power side of things
    like deadtimes and thermal management and so on - I'm just lacking on
    the micro end of things. That's basically the whole motivation for
    this project - a learning experience. I'm taking a 6 month sabbatical
    from work and I would expect my next employer is going to want to know
    what I did on my little vacation. If I end up with a piece of
    hardware that might be useful then so much the better.

    Ok on the pic Andy. I like hearing words like Simple & Basic. I'm a
    keep it simple kinda guy. I'll look into that micro for sure - that's
    the answer I was looking for.

    Got my DD214 too - I'm just another tin can sailor outta Pearl :)

    73
    Bob
    N9NEO
     
  9. Don Bowey

    Don Bowey Guest

    Did you happen to notice that most people bottom post on this board?

    Don
    Ex-W7SAT
     
  10. JeffM

    JeffM Guest

    Yzordderrex TOP-POSTED
    (also BREAKING THREADING and ignoring context):
    ....and just for kicks changed the Subject line
    to something without meaning to anyone else.

    :: Andy wrote:
    ::I like the PIC 16F84
    ::
    The PIC 16F84 is ANCIENT. If you can even find one,
    it will cost you more than a newer, more able PIC variant.

    Opinions differ on the "simplicity" of PICs.
    One of my favorite descriptions of the PIC:
    http://groups.google.com/group/comp...-*+immediate-addressing+A-good-place-to-start
    Scroll down Lindan's post
    and look at what he has to say about the AVR.

    Note: That group (comp.arch.embedded)
    is the place to ask questions about microcontrollers.
     
  11. colin

    colin Guest

    You can get motor control pic/mcu wich have the pwm module with the sine
    lookup table already.
    Im using a dspic30f2010 16bit with 3ch pwm wich would be able to do it
    easily.

    Colin =^.^=
     

  12. Good for you! :)

    Did you take advantage of the free meal at the Golden Coral
    restraunts yesterday? I went, but their Monday menu isn't my favorite.
    :(


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  13. Hi
    Look at www.analog.com ADUC702x is my favorite. PWM-Features included for
    gate-driving... AD and DA 12 bit @ 1 MSPS 40 MHz ARM7 core. Kits from $30 up
    to $279 (with usb-JTAG included) where available (in january 2007:-(

    Marte
     
  14. Yzordderrex

    Yzordderrex Guest

    Sure did notice that most bottom post here don.

    73
    NEO
     
  15. Yzordderrex

    Yzordderrex Guest

    Thanks for comments Jeff. And Yes, I'll be the first to admit I have a
    lot of bad habits when it comes to posting on these forums. I've had
    them a long long time and expect they will accompany me to the grave.
    Thats ok with me.

    When I changed the topic I was calling Andy directly to thank him for
    the input. Andy told me to take a look at the Pic products, not just
    the 16F84 in particular. I have heard others on other boards rave
    about the Atmel parts and I am sure they make a nice part. I know they
    have a large following. I am leaning towards the microchip products
    for two reasons. I have found an application note that does exactly
    what I need to do. I also have remembered that I worked with another
    engineer many years ago that is well connected with microchip. He in
    an independant consultant and writes application notes for them. I
    have been in contact with him recently as he was looking for some
    information from me. I will of course take a close look at the AVR
    parts before making any decisions. The main criteria is cost and time
    to learn. I'm presently in between jobs on a self imposed sabbatical
    and I'm looking for some resume building exercises.

    Thanks again for the input and if I have any Qs as the development
    effort goes forward I'll be sure to post to comp.arch.embedded. Below
    is a link to an inverter app note.

    73
    Bob
    N9NEO
    Just Say NEO!

    http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en010947
     
  16. Yzordderrex

    Yzordderrex Guest

    Nope, we don't have that restaraunt up here in MA. No Waffle House
    either that really bums me out. Mabe WH next week when wife and I
    travel to PA to see her pappy.

    regards,
    Bob
     
  17. Jim Thompson

    Jim Thompson Guest

    "Virginia is for Lovers", Florida is for ol' farts ;-)

    ...Jim Thompson
     
  18. Don Bowey

    Don Bowey Guest

    And continuous top-posting is for rude people.
     

  19. And you are SO jealous that we're accepted here, aren't you, Jim?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  20. Jim Thompson

    Jim Thompson Guest

    Arizona is for ol' farts, too ;-)

    ...Jim Thompson
     
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