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Simple multi-channel serial ADC (8-ch)?

Discussion in 'Electronic Design' started by Joerg, Feb 15, 2007.

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  1. Joerg

    Joerg Guest

    More like $5/1k, at least in the US: But not that much stock which always has me a bit worried. You couldn't
    even buy 1000 of them for that price right now because they only have
    597. Some of the non-stocked versions show this little note: "Obsolete
    item; call Digi-Key for more information."

    AD is known for analog excellence. Did you do a hard test down to the
    noise level against a stand-alone ADC? And look at clock beats and stuff?

    The other issue is that it's difficult to find local coders that know
    this uC. That is why we often default to the 8051 family where you can
    easily find contractors without having to pay lots in travel expenses.
     
  2. linnix

    linnix Guest

    You don't have to, we will do it for you.
    With a couple of MUXs, we can deliver 16 channels at that price.
    $5 for 1K is no problem for a 50MHz ARM.
    That's why you need hardware averaging, or low pass filtering.
    Hard to believe that. Where are you in?
    It usually takes a couple of days to learn a uC, most of the time
    dealing with I/O.
    If your contractor can't learn a new uC, look for another one.

    We can deliver the source code for the program and Jtag downloader via
    USB.
    You just need a 6 pins header (0.1" or 0.05" pitch) on your board.
     
  3. Guest

    Analog devices has 8051 version of their microconverters

    http://www.analog.com/UploadedFiles/Data_Sheets/ADUC814.pdf

    I have used them and with no bits toggling with a DC input, so noise
    is not a factor, but I also have used 10 bit AVR's and had only a
    single bit toggle, with 4x average you can get 10 bits without noise,
    and you don't need any external crystals. In any case you can do A/D
    converstions in sleep mode if your layout is not great.
     
  4. Henry Kiefer

    Henry Kiefer Guest

    LTC1090 or LTC1290 ?

    - Henry
     
  5. Hi Jörg,
    $ 3.98 from
    http://www.analog.com/en/subCat/0,2879,762%5F%5F0%5F%5F0%5F,00.html
    May be but this is only a example. Guess your very special AD wouldn't be in
    stock too.

    May be you want to use a very cheap ATtiny with a 4067 as Mux? I'm sure this
    isn't to beat. for low data rate you can create your own quad slope AD using
    the cheapest controller to be found.
    I saw the sample results from 1 Hz full scale sine wave without a plane or
    such special features just given to the minikit sampled there and
    transmitted this online with 2 kSps over UART (UART-USB-Bridge - Yes powered
    from USB! but with onboard 3V3 regulator). It looks fine without missing
    codes, only a few toggles around the last bit. In my view a very good
    result. I didn't expect more than 9 bits.
    It is a ARM7 controller and the only thing you need is the datasheet (handy
    vs 100 pages) and little knowledge of Ansi C. There are good examples from
    analog and around in the net.
    But If I were you I would use a cheap one and make my own dual or quad slope
    with a few 4051 mux in front of it as I remember you want to measure DC
    signals and mostly you design as cheap as possible for mass production

    Marte
     
  6. Joerg

    Joerg Guest

    I can do it for around $3, sans external mux. With an ADC chip ;-)
    Works as long as you don't have slower patterns in there. Seen that more
    than once on uC (we even ended up having to shut it down during
    acquisition).
    Sacramento, CA. No problem here to find talent in any field or uC. But I
    have clients in more remote locations.
    I might take you up on that some day. Just not for this project, the
    architecture is nearly done in analog/mixed but without any MIPS
    horsepower. There is another reason for not having a uC. The board needs
    to be super duper quiet 90% of the time when data acquisition takes
    place. There are some low level RF signals up to 100MHz that want to
    remain undisturbed.
     
  7. Joerg

    Joerg Guest

    Err, I clicked on it. Seems they don't have 1000 but only 490. They want
    $4.52 per chip if you buy them all.
    I am going to use something like the TLV1548, around $3-4. Plenty in
    stock, there are many similar ones. If the SW guys don't like the
    initialization chat I might spoof it like I described before. But maybe
    they don't mind.
    Slope might be a bit too slow because I need eight channels and SW guys
    usually prefer to read those in one fell swoop.
    That is indeed quite good.
    Or use a cheap 1-channel ADC and a HC4051. That's really hard to beat.
     
  8. Hi Jörg,
    I would prefer a µC so you can implement the control of the 4051 with the
    same timen than the ADC and the SPI/I2C or whatever else. Have a buffer,
    possibility of averaging... and the noise is almost from peripheral clocks,
    you don't need this with several µC. They can be very quiet, I guess more
    quiet than a discrete ADC with external oscillator pin.

    Marte
     
  9. Joerg

    Joerg Guest

    They also need a data-in sermon. Looks like older 5V devices, not too
    much stock, no TSSOP and very expensive. But thanks anyway, I'll see if
    LTC has more modern ones.
     
  10. Joerg

    Joerg Guest

    Yes, probably a uC could work here if clocked slowly. It doesn't have to
    do much. But there is one more pain left (don't I always find a hair in
    the soup?): Programming it. Beats me why companies like TI keep their
    SBW details a secret. They also do not provide a simple download tool.
    By simple I mean something that can be clicked from a PC and then
    automatically download into the uC. The user interface should consist of
    an *.exe file that gets double-clicked from Windows Explorer, no more.
    Currently you have to use one of the programming suites for that. I use
    IAR and I am comfortable with it but a biomedical engineer who does
    mostly mechanical and chemistry stuff won't be. I can't expect my
    clients to learn a design suite to program my boards. At least not the
    smaller companies among them.

    The analog/mixed solution I am designing now will not have that
    programming hassle. Somebody stuffs it, somebody tests it (probably me),
    then build a few dozen more, a tech tests those and then plops them all
    into the system rack.
     
  11. Hi Jörg,
    Don't tell such things. I'm really not the biggest programmer on earth, but
    I guess this may be the work for max half a day. For a programmer with
    practice it will be half an hour.
    I remember for ADUC there is a complete docu around, I guess it is general
    for the ARM7 derivates. At least LPC and ADUC can be programmed with a
    freeware tool available on the net (linux based, because the manufacturers
    supports only windows based programming tools ;-)
    That should be easy too. You only have to spy on the UART while programming
    and send this sequence to the controller :)
    The mspgcc guys may help here. I guess there is a downloader with command
    line support there too.
    Flashing is a very easy tool. this may be done by every person having the
    head not only on the neck to prevent the rain:)
    The time you search around will be longer than to program this little code,
    isn't it?

    Marte

    P.S. few years ago I thought similar. No µC if ever possible. But I see, the
    times are changing...
     
  12. Joerg

    Joerg Guest

    Coding is easy, I meant the download procedure (for people other than us
    EE types).
    SBW = Spy-by-wire, the download scheme for the new MSP430 F2xxx family.
    Some of those don't have a built-in UART anymore. SBW is a nice two-wire
    link. Would even be nicer if it was one-wire, maybe some day.
    If it has one. Why not use what's already there (SBW)? Why do they make
    that so hard by not releasing the innards of the protocol? I understand
    if someone doesn't want to disclose grandma's famous chocolate cake
    recipe but SBW can be reverse engineered if someone really wanted to.
    They might as well open it up which would increase sales.
    Not for SBW, AFAIK.
    Sure they can learn it but that takes time. It's the same as someone
    asking you to diagnose a modern car where the engine began to stall at
    times. I am sure you could figure it out but first you'd spend many
    hours learning because this ain't grandpa's old motor anymore. That's
    why they made those little connectors under the dashboard and a small
    hand-held diagnostic wand.
    Nah, it's pretty much done. It'll be a SPI converter. Either an 8-ch or
    a 11-ch depending on price and stock levels.
    I have nothing against uC, sometimes they are the tool du jour. But
    other times you can achieve a very robust circuit without. One that can
    be produced until long after this particular uC model has gone obsolete ;-)
     
  13. linnix

    linnix Guest

    Well, we are getting close to a simple downloading solution for ARM.
    We have a gdb server running on the target and jtag flash the chip via
    usb.

    We can remotely gdb the chip, or have a friendlier program (WinGdb?)
    to download it. The remaining work is to figure out how to interpret
    the AXF file. The goal is to:

    Compile in Keil (perhaps WinArm eventually), strip AXF into binary
    image. TCP it to the target (or programming box), flash it with usb
    jtag.

    Exactly as ordered. First function is to read and write the flash
    remotely. This will work with any FTDI 2232 based usb cables. We
    currently have a target running Linux 2.6.16 and an usb Arm. If your
    target is on static IP, you can remotely debug/download it across the
    country.
     
  14. Joerg

    Joerg Guest

    That's what is needed. Now if this would be available for a smaller uC
    such as the MSP430 I believe it would certainly increase its market
    penetration into areas that have gone without any uC so far. IOW not
    chasing the competition but truly new markets.

    IIRC from the Yahoo MSP430 forum there is a guy working on it but last
    time he was still looking for someone who would take on the PC side
    software. I don't want to spoil the broth here but, sorry, Linux isn't
    really an option. If you take me as an example none of my clients uses
    Linux. All Windows :-( .... ok, one MAC.

    I thought about a uC here after the discussion with Marte but will
    forego it again this time. This board needs good radio silence most of
    the time. The only way to achieve that within a few usec is to have an
    external clock that is gated and then it'll all become quite esoteric.
     
  15. Hi Jörg,
    AFAIK this is similar available for the older MSP430 series as well as the
    ATtiny.
    It shouldn't be a big problem to port to win32.
    But here you need to flicker around with the external clock while
    measurement are in progress while with a µC you can have the quiet while
    measurement and have the external clock only while transfering the data.

    Marte
     
  16. Guest

    why would your clients be programming your boards?
     
  17. Joerg

    Joerg Guest

    Hmm, that was the first question I fired off at the TI seminar. My
    question was whether there is a simple Windows-based code dump routine
    that would let non-programmers do a bootload. The answer was "nope".
    Later I asked again but the answer didn't change :-(

    Also, nowadays one really wants to embrace the F2xxx family (usually
    SBW-only) because older ones didn't even have a proper brown-out reset,
    among other things. By the time you add all that stuff you might as well
    go analog.
    It would be tough for me. Me and Windows frequently clash ;-)
    Sorry, I must have expressed myself without clarity. It's not data that
    is transferred but small signals that are extracted from other signals
    by that board. Pretty much down to the noise level. Then these are sent
    to other boards in analog fashion. During that time there cannot be any
    clocks and the pauses are very short. Just a few usec.

    While there are those few usec between measurement periods that isn't
    quite enough time to start a MSP430 which is already one of the fastest
    uC to come out of low power sleep mode.

    If you run SPI the whole clock scheme is under system control. I can
    request SPI to stop running after x microseconds no matter whether or
    not some task is completed, then resume after y microseconds. Probably
    this can also be handled by a uC as long as it is a fully static design.
    We did that in the early 90's with one from the 89C51 family. It was a
    very similar situation but in that case there was no choice because we
    had to run rather complicated communication with a connected device.
    Plus that client had expressed the desire to talk to this board with a
    Qume terminal (remember those?).
     
  18. Joerg

    Joerg Guest

    Because they are contractually their boards :)))

    But seriously, suppose they'd want a minor mod. With a proper downloader
    I'd do it, send it to them and tell them to connect the board, then
    double-click modgizmo.exe or something like that.

    Without, it goes something like this: Do the mod, go to the SWA or
    Jetblue web site, book flight, book hotel, book rental car, fly x hours,
    rent car, crash in hotel bed, drive to client, program boards, drive
    back to airport, get in traffic jam because some knucklehead speeded and
    spun out, miss last flight...
     
  19. Guest

    Yes but compare that to the mess that would occur if your customer
    wanted a mod to your serial based stand alone A/D board (it would be a
    HW mod)

    There is no reason why you can't consider a CPU based A/D a piece of
    unprogrammable hardware. Once you program it, put it on the board and
    make no accommodations what-so- ever to reprogram it. The serial stand
    alone A/D doesn't have that feature, and it appears it's acceptable to
    your customer, so why add it.
     

  20. Yes. How about a Lear Siegler ADM3?


    --
    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
     
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