555 monostable circuit is used as a table or capacitance resistance meter schematic

As shown by 555 and the timing resistor R1 ~ R3 and measured capacitance Cx can be composed pointer capacitance meter, one-shot circuit capacitance measurement principle is the

use Cx greater capacity, the greater the stability of the one-shot pulse temporarily that the voltage on Cx charge to the threshold level (2/3Vdd) the time required for longer. Due td 1.1RCx relationship, so when the input pulse triggers a fixed period, the output of the average amplitude of td (or Cx) is proportional to the relationship between the use of its amplitude of the ammeter to detect current flowing through the meter It reflects the size of the output pulse width td 555 size, which reflects the size of the capacity Cx. If the circuit Cx exchanged for a fixed capacitance C, and the measured resistance Rx R will be placed in a position, through the range change switch and recalibration of the table, the table can be used as resistance measurements. Figure b its waveform.

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