We have dual power supply units (+- 12V DC with common GND) at our college lab using which I am able to implement my project (digital thermometer) which uses op amps as shown in the figure.
I'm using an LM35, three op amps, an Arduino Uno, and an LCD display. I need to make this a product which can be run using only one external power supply (+12V DC adapter for the Arduino).
I tried using a voltage divider circuit to supply +6V and -6V DC to the op amps. However, when I connect the LM35, feedback resistors and other components, the voltages measured at various stages are not as expected. In fact, the input voltage itself changes it's value from +6V to +2V and the other voltage changes to -10V from -6V. One thing I have noticed is that there is a constant voltage difference of 12V between the input pins.
Why am I getting weird values of voltages? Is this called the "loading effect"? What are the other possible ways of supplying power to the op amps using the 12V adapter?
EDIT: This is the schematic that works with the dual power supply unit (+-12V) at my college. I want to make this device portable. Hence, I can't use the dual power supply all the time. Need a solution for this...