William K. Borsum wrote:
>
> Greetings:
> I've been following the PIC to FDC conversations a bit, and have a related
> question:
>
> I have an application where I need to log data at the rate of up to 200
> K-bytes per second, to a depth of 120-160 Mega-bytes.
> Part of the problem is that it is memory is broken up into a series of ring
> buffers that are sequentially  over-written till an event occurs, so flash
> or eeProm with a short finite life--or holes in the memory because of bad
> blocks--won't work.  Only viable alternative I've come up with is sRam, but
> the largest chips only appear to be 512Kx8, which means 200+ chips to get
> the total memory I need.  Oh yes--environment sees shock and vibration to
> 100+ G's, and the whole thing needs to fit in a can about 3.5" in diameter.
>
> Question: does anyone have a sneaky alternative that will work--like a
> micro-hard drive that will survive?  If so, how would the interface work?
> Has anyone implemented an IDE interface, or interface to a sRAM PCMCIA card
> on a PIC?
>
> Kelly

  sRam in PCMCIA form is *hideously* expensive, about $133 for a 4Mb
card, and you don't often SEE larger SRam cards than 4Mb.  40 of those
wouldn't be a good answer for you, I'd assume!

  Now a laptop (or 1.7" PCMCIA) HDD, that's a possibly do-able answer,
and more like $15-$20 for a 200Mb or so laptop HDD.  About 1 year
service life (if you leave the drive motor spinning constantly), shock &
vibration are a potential problem but these drives do handle some decent
forces (I suspect if you sprung it inside the can, with a little added
mass & some air damping or something, you could make it work, MAYBE -
depends on the amplitude of the vibrations.)

  Also, PCMCIA Flash Cards might be do-able (Sandisk makes 175Mb and
larger cards), except they'd get worn out by your application, right?
Same for laptop Flash drives (SanDisk makes these, act just the same as
regular laptop drives but they wear out after lots of writes.)

  Have you considered a set of battery-backed 72-pin SIMMs, or one or
two DIMM memory modules?  Seems to me that using that setup may be a
really good answer for you here (The storage media's fairly cheap, data
bandwith's NOT a problem, etc.)  Could sample the data to a PCMCIA drive
for downloading, or some such, perhaps.  That might be good (you'll want
a GOOD socket that's not going to vibrate loose, though these types of
sockets should be OK, I'd think - maybe tape the metal latches in place
to prevent any possible shaking loose of the RAM PCB's.)  I'd wonder if
DIMMs would stay in place well, here, have to help them stay in place
I'd think <G>

  Mark