I am working on detecting fingers being placed on guitar frets. My idea is to run a small voltage through each of the strings, a different voltage for each string. The player touches the string and makes the string touch the fret. On the end of the fret I detect the voltage with an Arduino (analog input). Since each string has a different voltage, the system can detect which string is touching the fret. So far, so good. But when two strings touch the same fret, I don't get the addition of the two voltages. The voltage goes down. How would I go about to solve this? How do I add voltages or detect multiple strings touching a fret?
I am using a 5V input and then using resistors as voltage dividers to get the different voltages for each string. See schematics attached.