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joshie75

Joined: 09 Nov 2010
Posts: 237
Location: Illinois

 Posted: 23 Feb 2012 06:47:24 pm    Post subject: 12V DC power adapter ground 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.
joshie75

Joined: 09 Nov 2010
Posts: 237
Location: Illinois

 Posted: 24 Feb 2012 11:35:36 am    Post subject: 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
benryves

Cemetech Expert

Joined: 12 Aug 2008
Posts: 1399
Location: London, United Kingdom

 Posted: 26 Feb 2012 09:23:54 am    Post subject: 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.
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