ToreB

IainM, thank you for the reference. My T-OBD has an inbuilt FTDI USB-serial chip, and my first earlier adapter versions were based on the schematic shown in this thead. A revised version of this schematic is also included in the scantool software package available on our website.
The present T-OBD is simplified using an IC for the OBD interface, not discrete transistors.
Cheers,
Tore