I've recently come into a situation where I have two grounds. My setup is as follows: I have a Sparkfun USB-UART breakout board that I'm using to talk to my microcontroller, and another that I'm using to power it and various other peripherals (sonars, etc). I think the different grounds are causing trouble because the breakout board doesn't understand the voltage pulses being sent to it
Can I safely wire my two grounds together? That seems like it could theoretically be dangerous - by wiring the two together I would be forcing quick shift in voltage levels in either my computer's USB port or the other power supply.
And one last question, I'm new to using my oscilloscope. I have a 15V battery pack I'm using, and the scope doesn't give significantly different readings for the pack's positive and negative end (only using 1 probe, probing sequentially). The scope is centered at 0V and when I first touch it to the 15V pack the signal shows a quick jump but then appears to continue resting at 0V. Why would that be?
Update: I just took a risk and wired the ground AND 3.3V connected to the USB port (that is the VCC on my UART board) and my alternate power source, and now it works. That seems troublesome to me though - what would happen if I had wired a 5V source to a 3.3V source?