Dmm As Frequency Meter

00 DMM AS FREQUENCY METER By providing a high-input-resistance multimeter (preferably of the digital type) with a frequency-to-voltage con- verter, it can be used to measure fre- quency. The range of the proposed device ex- tends from 10 Hz to 1 kHz on range A and from 1 kHz to 100 kHz on range B. The sensitivity for frequency measure- ments up to about 10 kHz is of the order of 35 mVpp, and for measurements from 10 kHz to 100 kHz about 350 mVpp. The input signal is applied to Schmitt trigger IC3 via limiters DI and D2. Bistables FF, and FF2, and IC2 form a monostable. When the monostable is triggered, it generates a pulse whose width is accurately determined by a 12- MHz crystal. The number of times the monostable is triggered per unit time depends on the input signal. The pulse height depends on the supply of the monostable. The supply is provided by voltage regulator IC4 and is about 5 V. At the output of the monoflop, i.e., pin 13 of FF2, there will thus be a train of pulses, ...