... but why are parts becoming so hard to get and becoming obsolete all of a sudden?
I don't think any parts have become obsolete in our world, with the exception of possibly two:
*The TLC5940NT, which is used in the MR16. But not only can it be replaced with the TLC5941NT, but Mouser has more than 600 of the spec'd part currently in stock and there appear to be a couple thousand available at distributors worldwide. While others have posted that the TLC5940 is end-of-life, there's nothing on the TI web site that confirms that statement.
*The MBI5027-GN, which is used in the Grinch and the LEDTRIKS. This chip is available only through a single source, King, and an alternate chip, the A6279EA-T, is in end-of-life (though Digi-Key theoretically still has about 2500 of them).
What we're seeing are *shortages* of somewhat obscure parts (I think the MER1S0505SC used in the dongle is a good example of that). For a part like that DC-DC convertor, there are long lead times to manufacture (16 weeks in its case) and a relatively high unit cost (probably $5 wholesale), so distributors like Mouser are reluctant to stock a lot of them and when they run out they only order a handful (250 in this case).
RJ will have to comment as to why he picked that particular part, but from what I can see on Mouser, it was the cheapest DC-DC convertor available that met the technical specs. I suspect most engineers would have chosen the same part for the same reason.
Even still, parts with specs similar to the MER1S0505SC at Mouser are kept only in quantities of 100-250; if you or I were to design a DMX dongle using one of those parts and 250 people decided to build our dongle, then Mouser would be out of that part for 16 weeks.
There are other parts in the dongle BOM that are backordered right now -- but they are just the warp and woof of electronics distribution. In the past, there have been true "jellybean" parts that are backordered -- capacitors and resistors -- which can be alternately supplied through (in the worst case) Radio Shack.
If a resistor or a capacitor is backordered on a BOM, you should not hold up ordering waiting for those pieces. Just delete from your order and post a plea here.
When Murata (maker of the DC-DC convertor) does a run of that chip, there will be enough for probably a year's worth of DMX dongle makers. But when the distributors run out, it will probably take four months to get another slug through the system again.
HTH.
\dmc
