Circuit Diagram of Capacitance/Frequency/Transistor Online D

When K1 is placed in II, then it can be used to test capacitance. 555, resistances from R8 to R12 and Capacitance Cx under test constitute monostable timing circuit. The larger the capacity of Cx is, the wider the pulse is. That is to say, if td=1.1(R8～R12)Cx is larger, the average current value is larger, and the indication of correspondent header is larger. In the circuit, BG1 is a unijunction transistor, and constitutes relaxation oscillator together with R1 and C3. Its output oscillator pulse signal is the trigger pulse of IC. When K1 is place in III, it can be used to test frequency. Under such circumstance, monostable circuit IC sends out fixed-width-value signal (td'=1.1(R8～R12)CB). When K1 is place in I, it can be used to test transistor. Transistor BG1 is responsible for the conversion of the positive and negative power.