Sound indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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When designing various automation and signaling devices, an audible indicator of the status of a particular node may be necessary. Often, such an indicator is built on the basis of an AF generator loaded on a sound emitter. However, the monotonous sound of such an indicator is often not noticeable enough, especially in noisy conditions. Therefore, signal modulation methods are used, for example, by interrupting it or changing the amplitude or frequency.
Although such devices have been repeatedly described in the technical literature, they were sometimes complex and critical to the supply voltage, they contained a large number of radio elements and winding parts.
The proposed indicator is free from such shortcomings, is not critical to the type of sound emitter and is able to operate with a significant spread in the supply voltage. The indicator (Fig. 1) consists of a control oscillator made on transistors VT1, VT2, a controlled oscillator on transistors VT3, VT4, and a power amplifier on transistor VT5.
The control oscillator generates triangular-shaped pulses that follow at a frequency of about 2 Hz and modulate the frequency of the audio signal. Its output signal is taken non-standardly - from the base of the transistor VT2 - and is fed through the resistor R5 to the base of the transistor VT3 of the controlled oscillator, made together with the transistor VT4 according to the multivibrator circuit.
The output signal of the multivibrator is fed to the power amplifier through the resistor R8. The amplifier is loaded on the dynamic head BA1, from which sounds are heard.
Transistors VT3, VT4 must be with a current transfer ratio of at least 80, and VT5 must withstand the current consumed by the sound emitter. The parameters of the remaining transistors are not critical. If the supply voltage does not exceed 4 V, the dynamic head can be at least 0,25 W with an 8 ohm voice coil. With a higher voltage, it is permissible to install low-resistance telephone capsules instead, for example, TA - 4, TK - 67, DEMSH - 1 A, DEM - 4M.
The design of the indicator is determined by the parts used. One of the options for a printed circuit board made of one-sided foil fiberglass is shown in Fig. 2. The insulating tracks are cut with a cutter made from a piece of hacksaw blade (if not available, a sharp knife will do). If desired, you can draw up a new drawing of the board for its manufacture by etching.
The board is designed to install ULM or MLT resistors, as well as the transistors indicated on the diagram. There are several holes for installing capacitors and a margin of the board area, which allows the use of various types of capacitors, in particular, MBM, BM, KM, K50 - 6. The appearance of the mounted board is shown in fig. 3.
The board is designed for fastening on the clamps of the battery ZSHNKP - 10B (from a miner lamp), for which two holes with a diameter of 6,5 mm are drilled on it at a distance of 107 mm. When mounting the board, the electrical connection of the battery clamps with the printed conductors is provided. To prevent corrosion of the board under the influence of the evaporating battery electrolyte, it should be covered with an electrically insulating varnish. From above, the board is covered with a lid, for example, from the kit of the specified lamp, but other options are quite acceptable.
When adjusting the indicator, the desired tone of the sound signal is set by selecting the capacitor C2, and the modulation frequency is C1.
Author: D. Volkov, Shakhty, Rostov region
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