Electromusical bell on the K555ID3 chip. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electromusical bell on the K555ID3 chip. Encyclopedia of radio electronics and electrical engineering

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

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Such a bell can be installed in the apartment instead of the usual electric one. And then, when you press the button at the front door, the apartment will be filled with the sounds of a popular melody that you choose yourself and program in advance.

The bell (Fig. 1) uses three microcircuits and seven transistors. On the elements DD1.1, DD1.2 and the transistor VT1, a clock generator is made that generates pulses with a duration of approximately 0,5 s. They go to the counter DD2, the outputs of which are connected to the decoder DD3. In turn, fifteen decoder outputs are connected through decoupling diodes VD1-VD15 and resistors R5-R19 to an audio frequency generator assembled according to the multivibrator circuit on transistors VT3, VT4. From the generator, the signal is fed to a power amplifier assembled on transistors VT6, VT7. The load of the amplifier is the dynamic head BA1.

(click to enlarge)

As soon as the SB1 button is pressed, the bell is powered from the GB1 source. At pin 17 of the decoder, as well as at the other output pins, a logic level 1 appears. The electronic key on the VT5 transistor opens, relay K1 is activated. With contacts K1.1, the relay blocks the button - it can be released. After pressing the button, the counter does not turn on immediately, but after a while, necessary for the relay to operate. For this purpose, a delay node is introduced into the call, made on a transistor VT2 and an element DD1.3. The duration of the delay depends on the resistance of the resistor R3 and the capacitance of the capacitor C2. Only after turning on the counter, the inputs of the decoder will receive signals in binary code. At the same time, the level of logic 0 will “move” at the outputs from the top according to the output circuit to the bottom, connecting one or another frequency-setting resistor of the audio frequency generator to the common wire (minus the power source). The dynamic head will emit the sound of the corresponding key.

When the logic 0 level appears at the last output (pin 17), the electronic key will close, the relay will release, the bell will turn off. In this design, you can use MLT-0,125 or MLT-0,25 resistors, K50-6 oxide capacitors, and the rest of the capacitors - KM-6. Diodes - any silicon. Dynamic head - with a power of 0,25-1 W with a voice coil with a resistance of 5 ... 8 Ohm. The relay is a reed relay or any other that operates at a voltage of up to 4 V and consumes a current of not more than 100 mA (the lower the current consumed, the longer the power supply will last).

The power source is four 343 cells connected in series. The details of the nodes circled in the diagram by a dash-dotted line are mounted on a printed circuit board made of one-sided foil fiberglass 1,5 mm thick. Resistors R5-R19 are soldered in the process of establishing a call.

Electromusical bell on the K555ID3 chip. Pay

Establishing a call begins with checking the operation of the clock generator. An oscilloscope is connected to the output of the DD1.2 element and the generator pulses are observed - they should be approximately 0,5 s long. If necessary, this value can be changed by selecting the resistor R2 or capacitor C1. Next, they check the operation of the counter and the decoder by the sequential appearance of a logical 0 level at the outputs of the decoder - an oscilloscope can also help here.

By selecting the resistor R5 (the rest are not yet available), the first tone of the selected melody is set, and then the remaining tones are set by selecting the appropriate resistors. At this stage, it is convenient to "lengthen" the clock pulse by temporarily connecting another one in parallel with capacitor C1, with a capacity of 20 ... 50 microfarads. In addition, instead of resistors R5-R19, it is better to turn on a variable or trimmer, the resulting resistance of which is then measured and a constant resistor of the same or possibly close resistance is soldered. If a pause is needed at some point in the melody, the resistor and the decoupling diode are not soldered to the corresponding output of the decoder.

In order for the bell to work properly, monitor the condition of the power supply elements and in case of a significant (more than 1 V) voltage drop of the source under load, when the bell is on, replace the elements.

G. Shulgin, Moscow, Radio No. 8, 1987, p. 54

Revisions

The method of programming a melody is very difficult and time consuming. The way out is in the translation of tones into the resistance of frequency-setting resistors (R5-R19). If, for example, we take the first octave, then for the “sol” tone, the resistor should be 12,8 kOhm, for “sol sharp” - 11,8 kOhm, “la” - 10,8 kOhm, “la sharp” - 9,85 .8,9 kOhm, "si" - 8,05 kOhm. In the second octave, the tone "do" corresponds to a resistor with a resistance of 7,05 kOhm, the tone "to sharp" - 6,25 kOhm, "re" - 5,5 kOhm, "re sharp" - 4,75 kOhm, "mi" - 4,05, 3,45 kOhm, "fa" - 2,95 kOhm, "fa sharp" - 2,5 kOhm, "sol" - 2,1 kOhm, "sol sharp" - 1,8 kOhm, "la" - 1,5 kOhm, "A sharp" - 1,2 kOhm, "si" - 0,8 kOhm. In the third octave, the tone "to" corresponds to a resistor with a resistance of XNUMX kOhm, "to sharp" - XNUMX kOhm. Now it is enough to select the desired fragment of the melody , determine the tones that make it up, select the appropriate resistors using an ohmmeter and install them in the bell.

S. Dobromirov, Kharkov

You can reduce the number of frequency setting resistors with the same number of tones. And, indeed, why install resistors R5-R19 if the melody consists of only five tones, alternating in a certain way? In this case, the anodes of the diodes (VD1-VD15) of the decoder outputs corresponding to the same tones must be connected together and connected to one frequency-setting resistor. As a result, the total number of design resistors will be reduced by a dozen. In addition, you can solder a capacitor between the collector and emitter terminals of the VT1 transistor (its capacitance can be 0,047-0,1 uF) and get an interesting effect: the bell began to “improvise” every time it was turned on by changing the duration of the sound of each tone. True, when the supply voltage drops to 4,5 V, the effect disappears.

V. Kandaurov, Gorky

If, for the time of establishing a call, a push-button switch with normally open contacts is connected in parallel with capacitor C1, then it will be possible by closing the contacts of the switch to “stop” the sound of the call at the desired tone and more accurately select the signal frequency with the appropriate resistor.

G. Shmakov, Myski, Kemerovo region

If there were no powerful output transistors VT6 and VT7, then you can use a free element of the DD1 chip in the output stage. The outputs 9, 10 of the element are connected to point 2 of the board, and the output 8 is connected to the middle output of the primary winding of the output transformer of the VEF-202 radio receiver. One of the extreme terminals of this winding was connected to the cathode of the VD16 diode, and the secondary winding was loaded onto the dynamic head. city, p.51

Author: S. Apraksina, A. Martynenko, Meleuz; Publication: cxem.net

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