Arduino - Using NPN transistor as a switch to pull-up/down analog pin
So, I have a questions: - Am I going in the right direction using NPN Transistors? - What would the correct circuit be, etc.


Measuring the capacitance of a real-world object by charging via a 1M resistor is probably not the right approach as the currents involved are very small and the circuit is not likely to measure reliably. Further, connecting external objects directly to Arduino pins is probably not a good idea due to the chances of ESD destroying your Arduino after some amount of use. For those reasons I think you need to first take a little step back.

I suggest starting with measuring the capacitance by using an oscillator whose frequency will vary depending upon the capacitance. You can then measure the frequency via a circuit that converts frequency to voltage for your ADC. Circuits for both of these you should be able to find elsewhere.

That done, you should be able to build a detector for the sensor contact on top of your capacitance detector. You will have several discrete states of contact for your various sensors - eg no contact, weapon A contact with lame B, weapon contact with wrist guard, etc. Draw a table for how the your circuit behaves when the sensors are in each and every possible state. You may have enough "information" in the existing circuit, or you may need to augment it slightly.

I hope this helps point you in the right direction.