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.
24K 1/4 Watt Resistor
56K 1/4 Watt Resistor
3300pF 25V Ceramic Capacitor
47uF 25V Electrolytic Capacitor
10uF 25V Electrolytic Capacitor
1N4148 Silicon Diode
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.
Source: Electronics Lab