converting digital signals to analog
Feed all 12 signals via equal value resistors into a summing node of an op-amp like this: -



But remember this is an inverting summing circuit so you'll need another op-amp inverter on the output to convert from negative voltages to positive ones.

Just four inputs are shown for clarity with R1=R2=R3=R4. Make them all 10k for instance. Rf then is used to set the gain. If V1 is 5 volts and you need -0.83 volts on the output then Rf is 1660 ohms but don't forget to invert this back to +0.83 volts.

Compare the above with a circuit that is more conventionally regarded as a proper DAC. It uses weighted resistor values on each digital input: -