PWM switch

This might be a stupid question, but I'm getting stuck in my thinking here. I'm designing a device that will be activated by a typical RC receiver that is putting out the standard PWM. My device will be on a separate power supply (battery) than the receiver, and I want to keep it that way. I'm guessing I can't just have the signal from the receiver feed into my device without a common ground of some sort. How do I make sure my device reads the signal reliably while keeping the power supplies as separate as possible?

Well, I may have found my own answer on the web. It appears there are PWM switches out there that are optically isolated. I suppose I could do the same, though it adds more complexity to device. Any other ideas would be appreciated.

PWM is nothing more than chopped DC with varying marks/apce ratio, depending on the frequency of your PWM, whats wrong with standard opto isolators? Many designed for switched mode power supplies can work up to 200khz (I think..) and have a logic compatable output.

Isolation

The opto isolators are very safe. If something goes wrong with your motor controller there is no path back to the receiver. You can interface the two simply with just a common ground however.

I just realized that opto-isolaters are a pretty standard device and can easily be found at digikey for a low price. It looks like I can optically isolate this and still keep the part count pretty low. I'm going with opto-isolation. Thanks for the replies.