High precision frequency and voice detector

Here is a very interesting and useful project high precision frequency and voice detector made from IC LM567 and can be used for detecting frequency with high precision and it also detects voice.

Circuit description of high precision frequency and voice detector 

The main part or heart of the circuit high precision frequency and voice detector is IC LM567 which comprising a phase locked loop (PLL), and detect frequency range between 0.01 Hz to 500 kHz. The value of detection of frequency and voice detector can be changed by changing the value of low-pass-capacitor. The formula for calculating the value of low pass capacitor is

L.C = n/Fr

Where Fr = 1.1/(R2 * C2), while n= 1300 for two percentage detection bandwidth and 6300 for 14 percentage. 1.1 kHz PLL running frequency is set by R2 and C2.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 22 KΩ

R2, = 10 KΩ

R3 = 1 KΩ


C­1, C2 = 0.1 µF

C3 = 1 µF/16V

C4 = 2.2 µF/16V


IC1 = LM567

D1 = LED

D2 = 1N914


6V relay



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