I have a HDD which has serial access but needs 1.8v TTL serial. I only have 3.3/5v serial devices. The standard PL2303, A UART Usbbee, and a generic serial adapter. The PL2303 & generic have 3v/gnd/txd/rxd/5v pins and the USBbee is pictured below.
I found some LM1117 regulators which can take in 3-12v and have 1.8v output.