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serial memory; help select for serial A/D, D/A

Discussion in 'Electronic Design' started by [email protected], Jan 3, 2008.

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  1. Guest

    Electronics hacker.

    Trying to design and build a very cheap "digital audio recorder".
    I've located some cheap a/d d/a's with serial memory interfaces from
    Microchip. I'd like some suggestions as to memory section. I've
    never used and not familiar with serial ported memory. I'll take
    care of signal interfacing but, wouldn't it be nice to have something
    that just "dropped" (or cooperated) into place.

    The circuit will record audio until instructed to playback. Then it'll
    just playback the last n seconds forever.

    Thank you.
  2. donald

    donald Guest

    Lets take some timing into consideration.

    At 8 kHz, that's a sample every 125 usec.

    So a memory that can write a sample every 120usec would work.

    Or a block of data written to a block device.

    The block size would determine how many samples you would need to read,
    then write those samples to the block device.

    Add a few more numbers to this and you'll have your design.

    You will also have the requirements for the processor you will need.

    good luck.

  3. Guest

    Here are the specs - 2 channels, 10K,. 50us and 30 seconds of data...
    30- MBs? They even make it that large? But what I'm looking for is a
    memory part number or mfgr type that would work well. What's the
    2n2907 of the memory world? What would interface well with these
    serial a/d d/a's. Is there a standard serial memory part everyone
    uses? What about a serial memory with a separate input and output.
    that just clocked to the next location? Do they make one? I know
    they used to make 'paged' chips that clocked out a "page". No
    addressing, just round and round. And no processor, a sequencer.
    Thanks Donald. You've been helpful. Happy new year too.
  4. Guest

    Oops... should be 300 K?
  5. donald

    donald Guest


    OK, let me understand what you are asking.

    ----- -----
    | | | |
    | a/d |----/#/---| mem |
    | d/a | | |
    ----- -----

    So you want to connect the a/d - d/a to the memory directly ??

    I don't think this will work, I don't know of any a/d-d/a or mem that
    can act as a master.

    These devices are slaves to some master device.

    Use a PIC. ( ok thats out of the way )

    You will need to program some sort of device to go in the middle.

    There are all sort of devices, PIC, AVR, MSP430, Motorola HS8, as well
    as programmable logic devices.

    These are just a start.

    Let me know what you have in mind.

  6. donald

    donald Guest

    Oh yea, is this a one off project or will you need many of these ?

  7. Hi,
    You might want to look at this article first.
    You should be able to adapt this easily to your requirements.
  8. how about using a chipcorder?

    alan nishioka
  9. Guest

    Thank you all for your help.

    I want to build a dozen. They are gifts... for Christmas... last
    Christmas. :)

    For control logic I was hoping to find a sequencer and skip any uP
    like the PIC (which I don't know how to program and wonder if they
    could supply fast enough control of the recording loop). I used to
    program PALs a lot and remember there were devices I called
    sequencers. They had programmable memory that was just clocked out,
    glitch free. A few inputs could select banks of preprogrammed signal

    ^ ^ ^
    | | |
    [[[ sequencer ]]]

    As to the chip recorder - a fidelity issue. I would like 10khz
    bandwidth and 30 to 60 seconds record time.

    Dan, Rread
    .. Hummmm. I'm rethinking my plans.

    (It would be nice to find a cheap schmatic capture program that I
    could use to post ideas.)
  10. TT_Man

    TT_Man Guest

    For serial memory , I use Atmel serial data flash (SPI) in all my products.
    Available from 1 m/bits to 64 M/bits in 8 pin soic.
  11. donald

    donald Guest

    Well, this will not be done without some sort of logic.
    The interface and timing of the sequencer will need to be designed.
    The a/d-d/a devices you have already picked out will need to be evaluated.

    So, what parts have you picked out ??


    PS: Maybe its time to learn how to program a PIC (or AVR or MSP or ....)
  12. Guest

    Well... maybe it is. Just a quick question. Could a PIC provide,
    say, 8 digial io ports and be able to update these in less than 10us?
    How much would that PIC cost. (There seem to be more PIC versions
    than stars in the sky) They have a developement board for <$100, but
    I don't know if it could be used.

    Also looking at the delta modulator mentioned above. That would still
    require control. I'd have to gin up a very deep shift register.

    Thanks again and again.
  13. donald

    donald Guest

    8 digital io bits ??

    10usec ?? I don't understand what this means.

    Ok, there are lots of PIC boards out there.
    I use these from time to time:

    First is to count the number of io bits.

    The a/d - d/a parts have x number of io bits to operate, which I still
    do not know which one you are looking at.

    The memory device has y io bits to operate. Which has not be chosen yet.

    So, how many io bits are required ??? Not a clue, until you make some

    Isn't design fun.

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