How to make a +, a - voltage and gnd ?

[Hextejas]

I don't know how to do this but I think it might be simple.
I have a project that requires a +15, a -15, and a gnd. Both DC if that makes sense.

I have 2 different voltage source, both have a red and green 15 volt connector.
So how to hook them together and where does that silly gnd come from ?

Thanks

Oh yeah, another student while wrestling with this same problem, mentioned a voltage divider but I don't know how that would work so I am going to go read up on it.

[Nusa]

Depends on what your "voltage sources" are. If they're proper isolated bench supplies, it's easy -- just hook two 15V supplies in series to get a 30V supply. Then you simply change your GND reference...what was 0, 15, and 30 V can also be looked at as -15, 0, and +15 V. 0 (aka GND) is chosen reference point for everything else.

If they're NOT isolated supplies (e.g. most wall-warts and computer supplies), I would not recommend that at all.

[danadak]

Post the manufacture name and model number of the supplys.

If no markings some pics might help.

The resistor divider approach works OK if the current in the supply rails
very low, otherwise its best to use a buffer to create the virtual ground,
that avoids supply droop with load.





The above example, examine output current spec, and take care to note worst case power dissipation.
If your load exceeds OpAmp capability then asomething like this -






Regards, Dana.

[Hextejas]

They are both isolated supplies so I will give it a try tomorrow.
Thanks