So, a bit of backstory. I got this Sanguinololu put together, along with a 12v power supply that has an LED next to the rail letting you know when it's live. The PS doesn't have a switch on it at the moment, so I leave it unplugged from the wall when I don't need it. So it was connected to the screw terminals on the motherboard, but without wall power. I plugged the USB cable in and got a good connection to the computer. I noticed that the LED on the PS's rail lit up, which I thought was weird, but I didn't think hard enough about it. When I plugged the PS into the wall to give the motherboard 12V my laptop instantly shut down.
Turns out that's because the 12v side of the Sanguinololu is crossed over to the USB's power side. So with just the USB plugged in the voltage regulator is providing the expected 5v on one side, but also putting out 2.5v on the 12v side. When just the PS is connected, the 12v side has 12v, and the 5v side has 5v, but the USB also has 3.5v.
That's not supposed to happen, right?
I can't have both the USB and the PS plugged in, because it puts power back through the USB cable into the laptop.
I double checked the installation and orientation of the voltage regulator and associated capacitors.
Turns out that's because the 12v side of the Sanguinololu is crossed over to the USB's power side. So with just the USB plugged in the voltage regulator is providing the expected 5v on one side, but also putting out 2.5v on the 12v side. When just the PS is connected, the 12v side has 12v, and the 5v side has 5v, but the USB also has 3.5v.
That's not supposed to happen, right?
I can't have both the USB and the PS plugged in, because it puts power back through the USB cable into the laptop.
I double checked the installation and orientation of the voltage regulator and associated capacitors.