Entertaining experiments: a dynamic head is a toy dance floor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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As you know, a dynamic head converts the electrical vibrations of sound frequency supplied to its coil into sound. It happens like this. The voice coil is placed in the gap of a cylindrical magnet between its poles. The frame of the coil is glued to a paper diffuser directed towards the listener. As soon as an electric current appears in the coil, a magnetic field is formed around its turns, which interacts with the field of the magnet. In one direction of the current, the coil is pushed out of the gap, in the other direction it is drawn into it.

If an alternating current of sound frequency flows through the coil, the coil oscillates in the gap with the same frequency. At the same time, the diffuser also oscillates, creating sound waves - we hear them.

After such a brief digression into the theory, let's start experimenting with a dynamic head. You will need a 1-2 W speaker head with a 4-8 ohm voice coil, a bell button and a 4,5 V battery (it can be made up of several series-connected galvanic cells). Connect these parts in a serial circuit (Fig. 1). Attach a wire bracket to the metal rim of the head and tie a piece of sewing thread to it with a light wooden or plastic ball at the end - it should lie. on the diffuser. Press the button A current will flow through the voice coil, the diffuser will pop out and throw up the ball. (If the cone, on the contrary, retracts, you will have to swap the conductors suitable for the leads of the voice coil or power source). By pressing and releasing the button at a certain pace, you can make the ball do various pirouettes in the air.

Connect the dynamic head in parallel with the head of the radio receiver or instead of it - the ball will bounce to the beat of the music. You can use the broadcast network and include the head in it, but through a step-down transformer TorT1 and a variable resistor R1 (Fig. 2). The resistor can be used to adjust the volume of the sound, which means the amplitude of the diffuser oscillations and the height of the bouncing of the ball.

It is better to use a transformer from a subscriber broadcast loudspeaker designed to operate from a 15 V network. If it is not available, as an exception for experiment only, make a transformer using nails as a magnetic circuit (Fig. 3). For such a transformer, you first need to glue a cylindrical frame from thick paper with cheeks along the edges. The inner diameter of the frame can be 15...20 mm. length - 20...25 mm. A secondary winding is wound on the frame, turn to turn - 100 turns of PEV or PEL wire with a diameter of 0,3 ... 0,4 mm, and on top of it - a primary winding, consisting of 2000 ... 2600...0,12mm. After that, nails are inserted inside the frame on both sides.

Music pieces transmitted over the broadcast network will now be accompanied by the sounds of a bouncing balloon and its pirouettes in the air.

The final stage of the experiments was the manufacture of an original toy in the form of an unusual dance floor (Fig. 4). On the table is a small box in the form of an impromptu stage with a figure of a dancer on the stage and two control knobs on the front wall. The turn of one handle - and the stage was lit up, the music began to play, the dancer "came to life", began to dance, performing the most intricate movements with his arms, legs, and body to the rhythm. By turning another knob, you can select the optimal illumination of the scene.

"Dance floor" consists of several parts. The main stage is 6. made of plywood or other durable material 5...8 mm thick. The stage has no bottom, and a hole for the dynamic head 11 is cut out in the top cover. A circle 12 of drawing paper is glued to the head diffuser (inside the corrugation) with rubber glue. On this mug there is a figurine of a dancer 5. The torso of the figurine is cut out of a light material, say balsa, and the tubes for the arms and legs are made of dry elderberry or also balsa. A sewing thread is passed through the tubes and attached to the body so that the tubes are easily bent relative to each other and the body. Using the same thread 4, the figurine is attached to the ceiling 7. In this case, the dancer's legs should touch the circle of the dynamic head, but not bend.

In front of the stage, a U-shaped drain 10 is attached, made of cardboard or thick drawing paper. The front of the rack should be designed like this. to give the impression that these are curtains and curtains, as well as a stage barrier.

Holders 8 are fixed in the corners of the rack from the inside - two in each corner at some distance from each other. They are made from cardboard. Small-sized lamps 9 are screwed into the racks, which are connected by conductors to the parts of the electrical circuit located inside the stage.

The ceiling 7 is glued from cardboard or thick drawing paper and glued to the stand 10. C3adi to the stage and ceiling are attached with screws 1 wall 2 with a decorative panel 3 pre-glued to it - this can be a suitable illustration from a magazine or your own drawing. By the way, PVA glue is most convenient for gluing cardboard and wood.

Now, probably, it is clear why the dancer's figure will dance. After all, it touches the paper circle of the dynamic head. It is worth giving an audio frequency signal to the head - and the circle, together with the head diffuser, will begin to oscillate up and down, as in the experiments described above, which means tossing the dancer's legs. The figurine will move. Although the vibrations of the circle are barely noticeable to the eye, their speed and the force of the push are sufficient for the figure to jump relatively high, imitating the pirouettes of a real dancer.

On fig. 5 shows a diagram of the device. The first control knob is a variable resistor with switches SA1.1 and SA1.2. This is the regulator of the signal coming from the broadcast line through the TT transformer to the dynamic head BA1, in other words, the volume control. The second control knob is a variable resistor R1. They change the brightness of EL1 lamps. EL2 lighting up the stage.

The transformer can be ready-made or home-made - it was described above. Lamps - for a voltage of 2,5 V. If the illumination of the stage is not enough, you will have to install two parallel-connected lamps for a voltage of 3,5 V from a flashlight. It is possible that instead of a battery, the toy can be powered from a network adapter.

Author: B.S. Ivanov

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