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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Electronic swing. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur The toy swing, loved by all kids, can be made to swing "forever". For example, by making them electromechanical. This will require an electromagnet, a battery and a pair of contacts closed by a swing suspension (Fig. 1). If a swing with such an electromechanical device is given an oscillatory motion, then with each closing of the contacts, a current will flow through the electromagnet winding, the magnetic field of which will attract the armature. It is only necessary to set the opening ledge of the swing suspension in such a position that the contacts close only for a moment when the armature approaches the core of the electromagnet, giving the armature, and hence the swing, an additional portion of kinetic energy - just like we push an ordinary swing at the moments of passing the equilibrium position .
After opening the contacts and the disappearance of the magnetic field, the swing by inertia will pass the equilibrium position, reach the top dead center and begin the reverse movement. But during the reverse movement, the swing suspension does not close the power supply circuit of the electromagnet winding. Thus, there is a one-sided "pushing" of the swing by the magnetic field. The swing, that is, the amplitude of the swing oscillations, depends on the strength of the magnetic field created by current pulses in the electromagnet winding, on the length of the suspension and the distribution of mass along its length, friction at the suspension points, the rigidity of the contacts and the accuracy of adjusting the moments of their closing and opening. Is it possible, instead of mechanical contacts, the adjustment of which is rather complicated, to use a non-contact electronic switch for a swing? It is this device that we propose to use in toy swings. A schematic diagram of a non-contact electronic swing is shown in fig. 2, a. In them, instead of an anchor fixed on a swing board, a small but strong enough permanent magnet is installed. In the diagram, it is shown as a horseshoe over the core of an electromagnet with two windings. Winding II is included in the base, and winding I is the collector circuit of the transistor T1. The electromagnet is installed at the base of the swing exactly at the position of their equilibrium.
The initial state of the transistor is closed, since the base is connected through a low winding resistance to the emitter. At this time, an extremely small reverse current of the collector junction flows through the collector winding, which has no practical significance. When the swing moves towards the electromagnet, the permanent magnet, passing at a short distance from the core of the electromagnet, induces (induces) emf in the base winding. so that a negative voltage appears at the base of the transistor with respect to the emitter. This transistor turn-on voltage reaches its highest value when the magnet approaches the equilibrium position, because at this moment the speed of movement is highest and the magnetic flux through the base coil is at its maximum. By inertia, the magnet passes the equilibrium position. At this moment, the negative voltage on the base sharply decreases to zero and also sharply increases to the highest value, in the opposite sign. The transistor then turns off. As the magnet moves away from the equilibrium position, the positive voltage decreases, but the transistor remains closed. With the reverse movement of the magnet on the base of the transistor, a negative voltage reappears, which gradually increases as the swing approaches the equilibrium position and opens the transistor. This happens as long as the swing makes oscillatory movements. In this case, under the action of emf pulses induced in the base winding, the transistor periodically opens and current pulses appear in the collector winding, creating a magnetic field in time with the oscillations of the swing. This winding is connected so that when a current passes through it, its magnetic field attracts a permanent magnet. As a result, the oscillatory process of the swing is maintained. The energy of the magnetic field imparted to the swing is sufficient to overcome the friction in the suspension points, air resistance and other reasons that slow down the movement. The oscillation amplitude increases until the loss of motion energy becomes equal to the energy given to the swing by the battery. At this point, a constant swing mode will be established, which will continue until the battery power runs out. The transistor in this case acts only as an electronic switch. The diode shunting the collector winding prevents the occurrence of oscillations in it with a frequency determined by the inductance of the electromagnet, the mounting capacitance and the intra-electrode capacitance of the transistor. The fact is that when the transistor is opened, an oscillatory process occurs, which, due to the strong connection between the collector and base circuits, can be undamped. In this case, the control action of the permanent magnet ceases to manifest itself and the swing stops. The diode, cutting off the positive half-wave already of the first oscillation, prevents the occurrence of this phenomenon. On fig. 2b shows a diagram of the same electronic device for controlling the swing, but with two transistors connected according to the circuit of a composite transistor. This inclusion of transistors allows you to increase the current pulses in the collector winding and, consequently, the amplitude of the oscillations of the swing. A feature of both versions of electronic swing devices is that they do not consume battery power in the rest position. Therefore, there is no need to introduce a switch in the power supply circuit. To "disconnect" the battery, it is enough to stop the swing. The design of an electronic swing can be very diverse. It is only important to comply with some general requirements. First of all, it is necessary to ensure minimum friction in the places where the swing is suspended in order to avoid unnecessary loss of energy. It is best "if the swing suspensions are wire rings with a smooth surface. Thick silk threads have good flexibility and little friction. It is very important that the distance between the magnet and the electromagnet core at the point of balance is minimal and does not exceed 2-3 mm. You can not do the swing yourself, but use ready-made, toy ones (see the photo in the title of the article). Their thin cotton suspension should be replaced with a wire one and fixed on a horizontal bar with wire rings. From below, a ferrite permanent magnet or a flat magnet of a magnetic lock must be glued to the swing board (installed on the doors of kitchen tables, bedside tables). If the existing magnet is large in size, do not try to split it with hammer blows - it will demagnetize. You can separate a part of the magnet either by squeezing it in a vise, or by breaking it off without hitting it. Please note: the stronger the magnet, the better the electronic switch will work. The frame of the electromagnet windings is a cardboard sleeve with cheeks along the edges or a bobbin machined from some insulating material (Fig. 3). Wind both windings at the same time, putting together two PET!-1 or PEL 0,1-0,15 wires, until the frame is filled: 1; 1st frame. Inside the frame, insert a core machined from mild steel exactly to its internal dimensions. It is advisable to anneal the finished core, and then slowly cool it. The electromagnet is installed under the cover of the swing base in such a way that the end of the core is flush with the upper plane of the base cover. To do this, a corresponding hole must be cut in the base cover.
All other parts are also placed at the base of the swing: a circuit board with a transistor and a diode and two 3336L batteries connected in series (B1). In general, the transistor and diode can be mounted directly on the terminals of the electromagnet windings, if they are rigid enough. The battery can be attached to the base with a tin bracket, and all connections can be made with any insulated wire. If the installation of the electronic part is made exactly according to the scheme and all the details are in good order, then no adjustment is required - it is worth slightly pushing the swing to unbalance it, as they begin to swing with ever-increasing amplitude. If the swing does not work when you first turn it on, then turn on a 100 mA milliammeter in series with the battery. Then swap the leads of one of the windings. When it is turned on correctly, the arrow of the device will deviate sharply if a permanent magnet is quickly brought to the core of the electromagnet. Author: V. Ivanov; Publication: N. Bolshakov, rf.atnn.ru
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Comments on the article: Peter Did it in the 60s. Works.
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