How to create a negative voltage supply?
An easy solution is to use a 780X DC to DC power converter, you could even mock one up for use on the bench with wire and an iron. 

Below is shown for a 5V supply, they also have 12V or 15V that would be the same circuit but different part.

Do not get this confused with a 7805 linear regulator, a 7085 linear regulator will not generate a negative voltage and requires a negative rail. Because DC to DC converters can sink current, they can generate negative voltages.



Just to clear up confusion, this is a DC to DC converter:


Source: https://www.cui.com/product/resource/p7805-s.pdf