Greetings Parimala!
What sort of power lever are you anticipating? There are some relays available that will work with TTL voltage on the coil. If you need something beefier, you can use an intermediate power transistor between the serial port TTL output and the relay. As far as the actual serial communications is concerned, you can just transmit a continuous string of 1's to turn the relay on, or 0's to turn it off. (You might need to build a simple RC filter to take care of any chatter) I've used this technique with Hyperterm with good success)
Alternatively, there is a neat little SERIAL DAQ module available from B&B electronics that does a bangup job for controlling relays and such from the serial port. Last I checked, they were around 40 bucks
or so. {Note to Developer Exchange censors:(Am I allowed to mention other products on a National Instruments site? :)}
Eric
Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705
