In one of the magazines "Radio" ten years ago I read a description generator 3H logic elements and tips on increasing his volume. Thanks to this publication I was able to assemble the generator (see figure) only one digital logic chip CMOS structure, of the four elements which used only two. The generator I use to study Telegraph alphabet, but it can also be used as the detector in various electronic devices and toys.
The input and output of the first element DD1 is connected to the primary winding of the transformer T1 and are closed DC, which provides one hundred percent negative feedback and outputs the element in the linear regime. On the input and output of the constant voltage element is approximately half the voltage power and supply current is a few milliamps.
Alternating current with the frequency of the sound element is inverted, so the findings the transformer comes out-of-phase audio signal that is required for it to work.
But the vibrations of sound frequency should be instituted in our generator. For this signal from the output of the element DD1 again inverted by the element DD2 and through the capacitor C1 is input to the first element. Thus, it appears positive feedback is necessary for self-excitation. Telegraph key put in the food chain.
Transformer T1 serves for matching high impedance output of the generator with low-impedance load - dynamic head of BA1. Will fit any output the transformer is from a small transistor radio. The average output of its the primary winding is not used. The tone of the sound can be varied by selecting capacitor C1, - increase its capacitance lowers the frequency.
If the remaining two logical element chips are not used, their inputs (findings 8, 9, 12,13) to be connected to the positive power supply (pin 14). Then these elements will be in steady state (logical "O" on the outputs) and almost will not consume current from the power source. If the volume sound it is desirable to increase, the remaining items it is advisable to connect parallel to the element DD1. This will increase the current in the primary winding of the transformer, but accordingly and will cause some increase of the current consumed by power source.
The primary power source battery "Krona" or any other voltage 6...9 V. the generator worked steadily and with a partially discharged battery, which increased internal resistance in parallel connected to her findings oxide capacitor C2. The capacity of this capacitor is not critical, it can be 50 μf or more.
Author: S. Dolgov, Chistopol,Tatarstan