Using 4 voltages with resistors and an Op Amp, 4-bit binary code can be read by summing the output voltage. The source with the 15k resistor is V1, 7.5k is V2, 3.9k is V3, 1.8k is V4. All the possibilities of this 4-bit system.
0000 = 0V
1000 = -333mV
0100 = -667mV
1100 = -1V
0010 = -1.28V
1010 = -1.62V
0110 = -1.95V
1110 = -2.28V
0001 = -2.78V
1001 = -3.11V
0101 = -3.44V
1101 = -3.78V
0011 = -4.06V
1011 = -4.39V
0111 = -4.73V
1111 = -5.06V
