How do I use multiple voltages on a breadboard?

[Nightblade]

I have a breadboard which has one black knob with a ground symbol under it and three red knobs labeled V1, V2, and V3. It looks like this: http://www.globalspecialties.com/pr...owered-breadboard-premium/item/86-PB-104.html

I also have a bench DC power supply with one adjustable power supply with + and -, a 5 volt fixed power with + and -, and a 12 volt fixed power with + and -. (Three total power supplies each with a + and - ) It looks like this: http://www.extech.com/instruments/product.asp?catid=39&prodid=212

My confusion is why are there three negatives on the bench power supply but only one ground knob on the breadboard? What is the proper way to connect these up so that I can use all three different voltages on my breadboard at the same time?

I have tried a few different things myself and am getting some strange results when I measure with my multimeter between the pluses and minuses on different voltages. It seems that ground is not acting as ground except for the specific + it is paired with on the bench power supply.

 

[JimB]

The power supply outputs are completely independant from each other.
A term often used in this situation is to say that the supplies are "floating", that is to say they are not connected to each other and they are not connected to the chassis of the PSU.

So what you have to do is to link the -ve outputs of the PSU together and connect them to the common (black) terminal of your breadboard.

JimB

 

[KJ6EAD]

I have one of those breadboards also. Because it has many bus strips, when laying out a large circuit using multiple voltages, I use a strict color coding regimen of black for ground, yellow for +12, blue for -12 and red for +5. These are the same color/voltage pairings used in computer power supplies. I mark the bus with a thin strip of matching colored striping tape from a hobby shop and use matching jumper wires for all connections to a bus. This may seem like a lot of trouble but it's worth it to avoid confusion and simplify troubleshooting on a busy breadboard.

The independent supplies can be connected together to create unusual voltage and polarity configurations such as a +12V and -12V for op amp circuits. Using just the two fixed supplies for example, you should be able to get 5, 7, 12 and 17 Volts.

 

[Nightblade]

Thanks guys - this is helpful. Good idea with the color scheme - I think I will do that as well.

Using the keyword "floating" I am now able to find some more info on this... that is what I was missing before. I am reading this thread now https://forum.allaboutcircuits.com/showthread.php?t=7805