Identifying open switches in a serial circuit
If you're using a uC that has enough IO, you can go ahead and wire in a small capacitor to each junction you're interested in connecting to one I/O pin. Then set one pin to Input, the other to Output. Send a short pulse by raising the output from 0 to 1 and back to 0 quickly. Have the Input pin detect whether it received that pulse. If the switch is closed the pulse will be seen through the two capacitors. If it's an open switch, no pulse will be seen. Then just sequentially run through each of the switches performing the same operation described using the two I/O pins on each side of it.

This doesn't give galvanic isolation, but it does eliminate any issue of messing with your original signal.







simulate this circuit &ndash; Schematic created using CircuitLab