I run the risk of looking ignorant, but I am assuming that you are trying to control a "relay"? If so, I would use the parallel port instead of the serial port and connect a solid state relay (very, very low input current) to one of the digital lines. You can use inport and outport to set the values of the parallel port D,S, or C registers or use the "serial port write" function to the parallel port D register.
For a tutorial on the later visit:
http://www.advmeas.com/goodies/parallelport.html
This is an appnote by Advanced Measurements, Inc.
-Jim
