I forgot to mention that the isolation is not required. Here is a summary of my project. We buy a unit that controls DC motor. Right now we also buy an off-shelf wired remote control which has simple SPST switches to open or close what seems to be current loops (I measure
40mA when a loop is closed). We want to add a module between the remote and the control unit to allow or prevent some of the remote keys to function. This needs to be managed electronically (or digitally). A 0-5V signal would take care this. Also, I've been told that the the return path of the control signals is not connected to the unit's GND. Therefore, I can't put my module to the same ground reference as the unit.
In brief, a HI signal would allow the loop to close and current to flow and a LOW signal would open (or put in high impedance) the loop.
Thanks.