Train sound simulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators

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Many radio amateurs build all sorts of models of airplanes, ships, trains, cars and other equipment. However, for greater similarity with their prototypes, it is desirable to "voice" them, which will make them even more attractive. Consider, for example, the sound of a train. First, a gradually increasing noise of a moving train is heard, then near the station it gives a whistle about its approach, and when it stops, it noisily releases steam, making a sound reminiscent of "poof-poof-poof". Before departure, the station bell sounds, and the locomotive blows a farewell whistle, setting off.

We offer a description of a fairly simple sound effects synthesizer for a model of a passenger train with a steam locomotive. The block diagram of the synthesizer is shown in Figure 1. It consists of several independent blocks: a "puff" generator, a whistle generator, a bell ringing generator, a mixer, an AF amplifier with a loudspeaker. The description of the last block is not given.

Rice. 1. Structural diagram of a sound synthesizer: 1 - "steam" block, 2 - "whistle" block, 3 - "bell" block, 4 - mixer, 5 - ultrasonic frequency converter, 6 - loudspeaker.

Block 1. As can be seen from the diagram (Fig. 2), the base-emitter junction of the transistor VT1 operates in the breakdown mode and creates a continuous "white" noise (spike). This signal is amplified by the transistor VT2, operating near the closing threshold. Timer DA1 creates pulses with a frequency determined by the capacitance of the capacitor C1 and the resistance of the resistor R3. By changing the resistance R3, it is possible to slow down or speed up the "puffing" of the locomotive over a wide range. The pulses from the output of the timer are fed to the electronic key VT3. When the key S1 is opened, VT3 opens, the resistor R9 shunts the lower half of R10, and we hear a single "poof". If the switches S1 and S2 are closed, then a continuous hiss of the released steam is heard. Capacitors C4 - C6 improve the natural sound. The R1C2 chain protects the rest of the blocks from the penetration of impulses from DA1 into them.

Rice. 2. Schematic diagram of the block "steam"

Block 2. Transistors VT1 and VT2 (Fig. 3) operate in the circuit of RC generators with double T-bridges. The frequency of the first can be changed by a variable resistor R5. By adding their frequencies to R12, you can get new frequencies from zero to a frequency similar to the sound of a diesel engine. At intermediate positions of the R12 engine, various sounds are obtained, including the whistle of a steam locomotive.

Transistors VT3 and VT4 form a "white" noise generator, similar to the circuit in Figure 2. The outputs of all these generators for mixing are wired to resistor R18. The final amplification is provided by VT5. When the button SB1 ("whistle") is open, the resistors R22, R24 keep the emitter VT5 under a higher voltage than the base, and it is closed. When SB1 is closed, resistor R21 is grounded and shunts R24, thereby opening transistor VT5. Capacitors C16, C18 eliminate clicks on and off the whistle.

Rice. 3. Schematic diagram of the "whistle" block (click to enlarge)

Block 3. Here (Fig. 4) an RC oscillator with a double T-bridge is again used, however, with a resistor R14, it is set at the threshold of self-excitation so that the sound of the bell is the most natural. Timer DA1 generates pulses with a frequency of about 1 Hz, its excessively large output voltage is reduced by dividers R4, R1, then rectified by diode VD3 and differentiated by chain C4, R2 into short sharp triggering pulses. Opening the button, turn on the bell, giving one beat per second. If you reduce the resistance RXNUMX, the bell strikes will become more frequent.

Rice. 4. Schematic diagram of the "bell" block (click to enlarge)

Block 4. The outputs of all three sound sources are mixed in the mixer (Fig. 5). Each input has its own regulator (R1-R1). The signals are summed at the gate of the field effect transistor VT2. The total signal is fed to an external AF amplifier and a loudspeaker through a matching emitter follower VTXNUMX.

Rice. 5. Schematic diagram of the mixer (click to enlarge)

In this design, you can use the domestic timer KR1006VI1 or foreign R555D. Transistors in RC generators - KT3102 with indices G, T or KT342V. Transistors for noise generators should be selected according to the maximum noise voltage from the KT315 series with any index. The field effect transistor in the mixer is of the KT303 type with any index. The remaining transistors can be such as, for example, KT306, KT312, KT315, etc. Diode VD1 (Fig. 4) - any low-power silicon. All fixed MLT resistors with a power of 0,125 or 0,25 W. Variable resistors - any type with characteristic A (Fig. 2.4) and B (Fig. 5). Oxide capacitors - type K50-6 for 25 V. Permanent capacitors in the circuits of RC generators are metal-paper with a tolerance of 5%, the rest are any. Start buttons - any, for example, P2K, etc.

It is most convenient to perform each block on a separate board. Installation can be both hinged and printed. The location of the parts in the blocks is not critical. After assembly, each block is checked and adjusted using a high-impedance headphone (headphone).

Supply voltage +15 V (permissible + 12 V). In noise generators, a voltage of +7,5 V is set on the collectors of transistors by selecting the resistances of the base resistors (marked with asterisks). Paired resistors and capacitors in the bridges must be selected as accurately as possible, otherwise generation will not occur. The voltage of +7,5 V at the drain VT1 (Fig. 5) is set by selecting the resistance R8. Use the short ends of a shielded cable to connect all units to the mixer. The same cable is needed to connect the mixer to an external AF amplifier.

The power supply can be any low-power 15 V. It is desirable to install all units on the chassis using connectors. The main controls are displayed on the front panel of the case. The dimensions and shape of the case are arbitrary.

Connect the mixer output to the AF amplifier and loudspeaker, apply power. Now, in block 3 ("bell"), adjust the resistor R14 according to the optimal sound when the SB1 button is pressed, while there should be no clicks or other extraneous sounds.

In block 1, it is desirable that the three main controls are located side by side on the front panel. This is the handle of the resistor R1 ("frequency"), the button S2 (turn on "poof") and S2 (release "steam"). Then they can be controlled with the fingers of one hand. Block 1 has only one operational button SB5. The tuning elements R12, R18 and RXNUMX are located on the board, they are configured during commissioning and are not displayed on the front panel.

If your train model is equipped with an electronic speed controller, then it makes sense to connect the block 3 controller R1 with the train speed controller for more consistent control of the two.

In addition to the sound addition, lighting design can also be added to the train model, depending on the taste and capabilities of the modeler.

Author: Yu.Pakhomov

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