frequency meter - with good accuracy at low frequencies

with good accuracy at low frequencies Intersil IC type 7226B is just the right counter for a simple but reliable fre- quency meter which covers a range of 9 MHz. The circuit of the meter divides into four functional sections: • input stage, T1, T2, N2, N3; • multiplier, FF1, FF2, IC3, IC4; • counter, IC5; • display, Ld1 . . . 6 In general, the circuit is a standard design, much of which has been described in earlier issues of Elektor. The primary function of the input stage is converting the input signal into rectangular pulses that are fed to the counter either direct or via the multiplier. The stage can handle in- put voltages of up to 50 V r.m.s. which is sufficient for most measurements. Diodes D1 and D2 conduct when the input voltage is above about 600 mV so that the in- put impedance is determined primar- ily by the value of R2, that is, around 1 M. The multiplier ( x 100) is particularly important for the measurement of frequencies between 5 Hz and 1 . . . 2 kHz. Th...