Multiple batteries, one ground?

[mstacho]

I'm going to need to draw a lot of current to power my motors, so I don't want to have the same battery driving my axon (or any other uC) as drive my motors.  My motor driver chip allows this. Problem is, since the "grounds" for each battery are at a different voltage relative to each other, I can't send a power-on signal to my motor controller through my uC.

What happens is this:

I send +5V, from the axon digital output (and so +5 relative to the axon's power source) to the motor controller.  When I check the voltage against the axon's power source, it is indeed +5V.  But when I check it against the battery powering the motor, I get only +0.35V.

Is there a way to connect two batteries to a common ground without having them interfere with each other?

MIKE

(ps: this may be a very simple question, so apologies in advance!)

[mstacho]

Oops, sorry, this question was already answered here: http://www.societyofrobots.com/robotforum/index.php?topic=1731.0

My bad.

MIKE