I used this in my atmega8 panel voltmeter on my diy power supply. It was meant to be able to measure both positive and negative voltages of up to 30 volts. This little circuit serves as a buffer and it also enables you to measure neg voltage using inverting opamp, but it's all powered by a single supply. All you need to do is multiply the adc result by 6 or -6 to get the actual voltage, 0-5V adc.
Of course you need to use a rail-to-rail opamp in order to measure voltages close to zero volts, but I used a LM741 because my power supply which uses this goes down only to 1,25 V (LM317-337) and so it's within the range of the 741 output characteristics.
Those power supplies in the EC represents the actual output voltages measured from the power supply. Change their values to see the output.
