8646 replacement (was: Unobtainium obtained!)

On Dec 11, 2012, at 8:45 PM, John Wilson wrote: Now you got me thinking about it. :-) The 8646A (assuming it doesn't differ significantly from the 8646 described in the KS10 manual) is too complex for implementation using SSI bits (2x parity gen, latch and flip-flop are a lot to stuff into one little board). But... Looks like this can be done with a tiny CPLD doing the latching, parity and enables; Xilinx has a 32-macrocell CPLD for just over a buck in quantity that fits in a 5x5mm QFN package. I'm assuming I can fit a 5mm QFN between the pins in a 300-mil carrier board, but I haven't actually tested that in layout. There's a handy little LDO available on the market (also for a buck in 1k qty) that does 3.3v, 1.8v and 1.5v in one 3x3mm QFN package, which gives us the I/O voltage, CPLD VCCint and the comparator reference voltage all in one tiny package. It's definitely the sort of thing that could disappear, in which case there's probably space for separate regulators (and the comparator reference doesn't strictly need a regulator, a simple potential divider would do, but as long as it's there, might as well...). If it all fits, it can be made in 1k quantities for just under $5 each (including the PCB and pins, not including assembly, not factoring in necessary parts overages for attrition). Selling the boards as a kit with the QFNs preattached and the CPLD pre-programmed seems like a valid option, though both fully-assembled boards and bare boards are workable for folks of differing soldering abilities and financial persuasions. So, here's the question. Is there enough demand to make a 1k quantity of this? I don't think a smaller volume is really going to be cost-effective. Building in 100 qty drives the PCB cost up from $0.69 to $4.43, and the per-part price goes up as well (not by as much); it would probably at least double the price per unit. Still, $10 each might not be bad for a replacement for a part that no longer exists, and it's a lot easier to raise a thousand dollars than five thousand. :-) I also haven't gone to the trouble of trying to fit this thing all on one board, so it may be infeasible with the specified load of parts or number of layers. I'm cautiously optimistic, though. Qty Part No Description Unit Total --------------------------------------------------------------- 1 XC2C32A-6QFG CPLD, 32 macrocell 1.07730 1.07730 1 AS1355-BQFT-WDG LDO, 3.3v/1.8v/1.5v out .54194 .54194 2 74LVC04-PWR Hex inverters, for 5v in .10725 .21450 1 MAX9108 Quad high speed comparator 1.81050 1.81050 2 2N7002DW Dual FET .06300 .12600 10 CAP-105 100nF ceramic cap .00462 .04620 2 M20-9991046 10-pin headers .12320 .24640 1 PCB Carrier board .69000 .69000 =============================================================== Total: 4.75284