/diy/ - Do It Yourself

>>1403252
For negative voltages:
Voltage is relative. That means that if you have a negative voltage, then it just means that your ground is at a higher potential than the "negative" voltage source.
Here's a crappy image I made to help illustrate.
Since we declare the middle contact between the two batteries to be ground, anything connected to the lower contact sees a negative potential with respect to our chosen ground.