problem with Interfacing IR receiver

[Nahian]

My IR receiver send 3-5 volt when it sense IR...and 0.6-0.7mV normally....
so easily the high (3-5)volt can turn on a 6v relay switch ....which will ground a i/o pin of microcontroller.but i cant just do the same thing by pc interfacing.......
high output from receiver turn on a relay switch to be short with ground pin with a status pin(0x379). but when the ground pin is grounded with circuit's ground(i hv outputs in the external circuit) the IR receiver sends -42v!!! normally, -37v when it senses(!!!).
Printer port is ok,and no problem with output.
external circuit's highest voltage 5V (regulated with 7805 and a smoothing capacitor)
what is the possible reason ? and what should i do?
thanks in advance.

 

[A.Anand Srinivasan]

is the circuit ground you are talking about connected to the PC or is it separate(i mean from something connected to the neutral pin or earth)....