1953naa

I too am having some difficulty sorting out the ProChrono serial port. I've tried to get it to work with a PL2303HX USB to TTL module as well as an FTDI FT232R USB to Serial module running at 5V and I get nothing but a CErr on the chrony. Switching TX & RX didn't seem to make a difference. Has anyone had any luck DIYing your own interface to the ProChrono? Is it 3.3 or 5V TTL level or is it true RS232 serial communication that is needed? What is the pinout on the ProChrono jack--- I'm pretty sure the base of 3.5mm jack is ground and I believe the tip is the TX from the chrono (connects to RX on USB adapter) but is this indeed the case? I appreciate any guidance members of this forum can provide on this! Ron