This simple circuit is a good solution to the powering a dual supply op amp
from a single battery problem. The circuit simply takes a positive voltage and
inverts it. It uses only one 555 timer and a few other passive components, so it
doesn't add much in the way of size and cost to a project.
Schematic
Parts
Part 
Total Qty. 
Description 
Substitutions 
R1 
1 
24K 1/4 Watt Resistor 

R2 
1 
56K 1/4 Watt Resistor 

C1 
1 
3300pF 25V Ceramic Capacitor 

C2 
1 
47uF 25V Electrolytic Capacitor 

C3 
1 
10uF 25V Electrolytic Capacitor 

D1, D2 
2 
1N4148 Silicon Diode 

U1 
1 
555 Timer 

MISC 
1 
Wire, Board 

Notes
1. V+ can be anywhere from 4 to 16V. V is one volt less than V+. So for 12V
output, use +13V input. The maximum current output of the circuit is about
280mA, more than enough for a few op amps.
2. For better regulation, a 79LOxx series regulator can be used.
3. A zener diode may also be used to regualte the output voltage.