Let's Make Robots!

Common Ground?

Noobie electronics question:

I built the tristate circuit nuumio posted a while back and managed to get it working with my picaxe 28x project board. I then tried to use it with an 08pic and a little breakout board I had created for it however, I can't seem to get it working. The 08 pic has two 100k pulldown resistors connected after the outputs pins on output 1 and 2 which are then connected to 4.5v ground powering the pic. My tristate circuit uses 4AA batteries to power the motors, with the only input being the two pins from the pic.

 

Is it that the resistors need to be connected to ground before the output pins? Or could it have something to do with not having a common ground? I'm not quite sure.

 

edit: sorry, forgot to include the link

http://letsmakerobots.com/node/17370

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Sounds like a problem of not having a common ground.  You need the grounds of both power sets to be connected so thaat the signals have a common relationship is one way of looking at it.

 

Pete