Despite difficulties in walking from one room to another and sitting at my workbench, I got in a bit of SMT assembly today:
Lessee now: micro-USB at one end, DE-9P at the other. Must be a serial-port dongle!
But why, you may ask, did I build my own USB serial port dongle? And what's with all the extra components?
It's isolated, that's what! And, yeah, there are isolated RS-232 dongles on the market, but I think this'll be cheaper (after I fix either a footprint or an ordering code, and thus eliminate the labor of converting a wide SO-16 into an SOJ). Won't have UL certification, and isn't really designed to provide safety isolation, but for eliminating ground loops when connecting to the debug ports of embedded systems it should be just the ticket.
Oh, and: no (0) through-hole components, so no pointy pins protruding from the back of the board on either side of the isolators.
It also has a little brother that skips the RS-232 transceiver, isolated power for the RS-232, and full modem control, and just provides TX, RX, and basic modem control at logic levels, using power from the target system. I haven't assembled one of those yet. For the folks using, e.g., Arduinos to control power systems with ill-behaved grounding, it ought to come in handy.
Update: Family photo with baby brother.
I'll entertain the possibility that the production version should use an SMT header.