A simple generator for learning the telegraph alphabet. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple generator for learning the telegraph alphabet. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In one of the magazines "Radio" ten years ago, I read a description of the 3H generator on logic elements and advice on increasing its volume. Thanks to this publication, I was able to assemble the generator (see figure) on just one digital logic microcircuit of the CMOS structure, of which only two of the four elements were used. I use the generator to study the telegraph alphabet, but it can also be used as a signaling device in various electronic devices and toys.

A simple generator for learning the telegraph alphabet

The input and output of the first element DD1 are connected to the primary winding of the transformer T1 and are closed in direct current, which provides one hundred percent negative feedback and brings the element to a linear mode. At the same time, at the input and output of the element, the constant voltage is approximately half the supply voltage, and the current consumed is several milliamps.

Alternating current with an audio frequency is inverted by the element, so an anti-phase audio signal is supplied to the terminals of the transformer winding, which is required for its operation.

But vibrations with sound frequency must still be excited in our generator. To do this, the signal from the output of the element DD1 is once again inverted by the element DD2 and through the capacitor C1 is fed to the input of the first element. Thus, a positive feedback is obtained, which is necessary for self-excitation. The telegraph key is placed in the power circuit.

Transformer T1 serves to match the high-resistance output of the generator with a low-resistance load - dynamic head BA1. Any output transformer from a small-sized transistor receiver will do. The middle terminal of its primary winding is not used. The tone of the sound can be changed by selecting the capacitor C1 - an increase in its capacitance lowers the frequency.

If the remaining two logical elements of the microcircuit are not used, their inputs (pins 8, 9 and 12,13) must be connected to the power plus (pin 14). Then these elements will be in a stable state (logical "0" at the outputs) and will practically not consume current from the power source. If it is desirable to increase the sound volume, then it is advisable to connect the remaining elements in parallel with the DD1 element. This will increase the current in the primary winding of the transformer, but will also cause a corresponding increase in the current drawn from the power supply.

The power source is the Krona battery or any other battery with a voltage of 6 ... 9 V. In order for the generator to work stably even with a partially discharged battery, which has an increased internal resistance, an oxide capacitor C2 is connected in parallel to its terminals. The capacitance of this capacitor is not critical, it can be 50 microfarads or more.

Author: S. Dolgov, Chistopol, Tatarstan

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