74HC4051 multiplexing and voltage divider
I see that you got your sensor schematic from the lucaszanella website.

Generally it's a bad idea to connect the transistor's base directly to a pad that anyone will be toughing with their finger. An electrostatic discharge can damage the base and short to 5V. Although 5V seems benign for most people it can be deadly for people with pacemakers.

What you should do is put a 10 mega Ohm resistor between the base and the sensor input.