Interfacing Issues

[William56]

I'm trying to interface a digital output from a computer to a I/O card using potter and brumfield I/O modules. I'm running the digtal outputs through a 741 op amp hooked as an inverter, because the I/O modules I am usin require a negative five volts to work. But when i hook up my computer while it is off, the op amp outputs the negative voltage necessary to turn on the I/O card. I'm looking for any helpful tips as this is for a group project and it has little time left and I have to have this circuit working in order to test out the program.

 

[(*steve*)]

You're using the output of a 741 to power something? Or is it just a level shifter (and possibly inverter)?

Is your problem that the circuit is turned on while the computer interface is unpowered?

Can you detect that the computer interface is unpowered? Does this suggest a solution?