Pocket frequency meter

pocket frequency meter 94by R Shankar Ti functions as a buffer, preceding Schmitt trigger Al, which has been dimensioned for a relatively low hys- teresis of about 18 mV to prevent the overall sensitivity being too strongly degraded. The output of Ai is fed direct to divide-by-two counter IC la, which is followed by three cascaded divide-by-ten IC sections. Sz selects the divisor and hence the relevant frequency range. Whatever range is This easy to construct circuit meets the demand for a simple, yet versatile battery operated frequency meter which can interpret signals with a minimum rms voltage of 10 mV and a maximum frequency of 100 kHz. The quiescent current consumption of the meter circuit is only 4 mA, which ensures a long life for the 9 V battery. Also of interest is the fact that the cir- cuit continues to work normally with battery voltages down to about 5 V. The meter input is protected up to 250 V AC. From the circuit diagram it is seen that the input signal is applied...