Turning a USB to RS232 adaptor into a USB to TTL serial adaptor by Aaron Brady:
I didn’t want to wait, so I had a look around what we had on hand. We did have a spare RS232 to USB adaptor. This one speaks the full ±15V, and I briefly considered using one of the spare MILSPEC SP232’s we got cheap to bring it down to TTL, but that seemed mad: there was going to be a MAX232 or similar in the serial adaptor bringing it up to voltage so it could go a couple of centimetres before getting stepped down again.
Here begins our adventure into very small wires, fine SMT soldering and hot glue.
We popped open the case, and there were two main ICs, a Prolific 2303 (the USB to Serial IC) and a ADM3251E (the RS232 line level convertor). I tried to desolder this with no success, but Bas stepped in, cut the leads with a craft knife and ran the iron over the chip’s leads and it basically fell off. He also did the very fine soldering to pins 1 and 5 of the Prolific chip, TX and RX respectively.
Project info at Aaron’s blog.