Leading the way to the Future
 23 Feb 2012 06:47:24 pm by joshie75 12V DC power adapter ground Quote Bored at my grandparents house and had five minutes to kill before we start a puzzle *yay*. So thought I'd ask a quick question so I might have replies when I get home later. I'm using a 120V AC to 12V DC power converted I scavenged off of an old router. So now that I have the 12V DC I need for my project; Now what about ground? Can I use the wire with "-" signs all over it as a ground for all the pieces in my project or? Here's my circuit.
 24 Feb 2012 11:35:36 am by joshie75 Quote I'm probably not qualified for a double post, but it's regarding my post above. I tested the adapter with my multimeter; I secured the wire with the -'s on it to the black tester, and the other wire was secured to the red tester. I got -12v DC. So does this mean the side with the -'s down it is actually positive? Thanks; Josh
The power supply's + terminal should be 12V higher than the - terminal. That is to say that if you use the - terminal as ground (which is typical) then the + terminal is +12V. If you were to use the + terminal as ground then the - terminal would be -12V.

I'm not sure how that's marked; the striped lead might indicate the positive side, not the negative side, though you can confirm this with your multimeter.

Op-amp circuits usually require a dual-polarity power supply, that is one that provides a ground, a positive supply and a negative supply. This is easily achieved by using two batteries:

 Code: .---o +9V   | -----  ---  9V -----  ---   |   +---o 0V   | -----  ---  9V -----  ---   |   '---o -9V

However, if you only have a single-voltage power supply then there are some techniques to generate the negative voltage from the positive one - an easy solution is to use a ICL7660 chip as that does most of the hard work for you.