...until I found this one which just uses a 555 timer, a couple extra caps and a couple of diodes (which can run upto 15 volts which is close enough for contrast)
Where did you get the +15V from in the first place?
The 555 will just produce some square waves, which can also be produced by a spare Arduino PWM pin... As this will give you -5V only @10mA (whilst the 555 can deliver 100mA) an all purpose NPN transistor is also needed, collector to the higher + voltage.
For peeople interested in this: DC-DC Wandler mit PIC
It is not English but you need not understand the text, it's all in the diagrams 