First, the basic model of the circuit is asymmetric multivibrator NOT gates, with some minor changes. As to why using asymmetric multivibrator to measure capacitance, since the electrical capacitance sensor during a game is very expensive, and there is a method of multivibrators 555, 555 is verified during the game but, when it reaches the resonance frequency about 400,500K unstable, but theoretically non-symmetric oscillation frequency of the multivibrator constituting the NAND gate may be up to 4M, we actually measured it can reach 2M, the higher the frequency, the more the number of last measured when the paper it's better discrimination.
