Musical toy Lightphone. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The principle of operation of the toy is based on changing the frequency of an RC generator, in which a photoresistor is used as a frequency-setting element. When its illumination changes, the frequency of the generator "floats", which means the tone of the sound in the headphones or dynamic head connected to it. So you can "select" the desired melody.

About "traffic lights" has already been described on the pages of the magazine "Radio" [1, 2]. But unlike them, the proposed two designs are equipped with touch volume controls.

On fig. 1 shows a diagram of a toy assembled on a logic chip and a transistor. On the elements DD1.1, DD1.2, a master rectangular pulse generator is made, the frequency of which is determined by the total resistance of the photoresistor R1 and resistor R2, as well as the capacitance of capacitor C1. With increasing illumination of the photoresistor, its resistance decreases, and the oscillator frequency increases.

Buffer stages are assembled on the elements DD1.3, DD1.4, and on the transistor VT1 - a power amplifier loaded on headphones BF1 (or a dynamic head with a resistance of at least 50 ohms).

The generator pulses from the output of the element DD1.3 (Fig. 2, a) are fed to the input of the element DD1.4 through a differentiating circuit consisting of a capacitor C2, resistors R3, R4 and sensors E1, E2. If the resistance between them is high, the capacitor C2 will not have time to charge during the action of the pulse, and the shape of the pulses at the input of this element will be almost the same (curve 1 in Fig. 2b). At the output of the element, short voltage pulses are formed (curve 1 in Fig. 2c), which open the transistor. The same pulses are sent to phones, but the sound volume is minimal.

With a decrease in the resistance between the sensors, when they are "overlapped" with a finger, the capacitor C2 has time to partially charge and the shape of the voltage at the input of the element DD1.4 changes (curve 2 in Fig. 2b). This leads to the fact that the duration of the pulse at its output increases (the curve in Fig. 2, c), and the volume of the sound increases. A further decrease in the resistance between the sensors leads to an increase in the pulse duration at the output of the element DD1.4 (curve 3 in Fig. 2, c), and hence the volume.

In addition to those indicated in the diagram, the device can use the K564LE5, K561LA7, K564LA7 microcircuit, the KD521A, KD503A, KD103A diode. Polar capacitors - K50-6, K50-35 or similar imported, non-polar - KLS, K10-17. Photoresistor - SF2-5, SF2-6, FSK-K1. Phones BF1 - TON-2 or other high-resistance (more than 500 Ohms), when using low-resistance phones or a dynamic head, you must install a KT972 transistor with any letter index.

Most parts of the device are mounted on a printed circuit board (Fig. 3) made of one-sided foil fiberglass.

The board is placed in an opaque plastic case, in which it is necessary to cut a hole with dimensions of approximately 10x30 mm. A photoresistor is placed opposite the hole at a distance of 20 ... 30 mm. The sensors are a plate of one-sided foil fiberglass with dimensions of approximately 20x30 mm, the metallization on which is cut with a gap of about 0,5 ... 1 mm in the middle along the wide side. The resulting two metallized areas are connected to the corresponding parts of the device. The disadvantage of this simple design is the dependence of the volume control range on the frequency of the master oscillator. It was possible to avoid it in a more complex "light phone" (Fig. 4), made on a microcircuit containing two op amps.

An RC rectangular pulse generator is assembled on the op-amp DA1.1, the frequency of which depends on the resistance of the photoresistor R10. A power amplifier was assembled on the op-amp DA1.2, to the output of which you can directly connect high-impedance headphones (say, TON-2). To connect a dynamic head with a resistance of about 50 ohms (for example, 0,5GDSH-9), the device should be modified in accordance with Fig. 5.

The device is powered by a unipolar voltage, therefore, for the normal operation of the microcircuit, an artificial "middle point" of resistors R8, R9 and capacitors C3, C4 is used.

The sound volume is adjusted using sensors E1, E2 - when the resistance between them decreases, a signal of a higher level enters the input of the power amplifier and the sound volume increases. The sensitivity of the touch volume control can be set with a tuned resistor R5.

In this device, in addition to the microcircuit, it is permissible to use the same parts as in the previous design, a tuned resistor - SDR-19. Most of the parts, including sensors, are placed on a printed circuit board (Fig. 6) made of double-sided foil fiberglass.

The board is also the front panel of the device, in which a window has been cut out to illuminate the photoresistor. On the side opposite to the placement of parts, sensors are located (shown by dashed lines). The board will be a cover of a light-tight plastic case. Light from any source should fall on the window. Closing the window with your hand or fingers to a greater or lesser extent, change the frequency of the signal, and touching the sensors with your finger, the volume of the sound. The harder you press the sensors, the louder the sound.

Literature

1. Dotsenko Y. Svetofon. - Radio, 1984, No. 11, p. 49.
2. Nechaev I. Electric musical instrument "Lightphone". - Radio, 1990, p. 60, 61.

Author: I. Nechaev, Kursk

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