Logic tester with acoustic indication electronic project

Using electronic scheme in the figure below can be constructed logic tester with acoustic indication. Acoustic tester in the figure below produces a low frequency sound when detects a logic 0, respective high-frequency sound when 1 logic is detected. The frequency produced by capacitors C1 and C2 depends. The input signal is supplied directly to the gate of N2 and reversed at the gate N3. If at input is detected, a logic gate N2 signal to pass through the amplifier A1. If a 0 is detected at input logic gate N3 signal to pass from the amplifier A2. The amplifier A4 form pulses from rectangular signal of the N4 gate which command transistors T1 and T2. With the buttons S1, S2 the oscillations can be turned on respective off. The circuit requires a continuous supply voltage between 5 and 10 volts and absorbs a maximum current of 10mA.

Circuit Diagram: 

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