Advanced musical metronome. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Musician

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In "Radio" No. 3 for 1996, an article "Musical metronome" was published, which found a wide response from readers. After some time, the author improved his design and today introduces her new version. The metronome, which allows not only to set the beat with sound "clicks", but also to play notes, can become an assistant for beginners, as well as professional musicians.

The musical metronome described in [1] is convenient in that the frequency of the musical tempo - from Largo to Prestissimo - can be easily controlled and adjusted to any musical instrument with a stable tuning. Any tempo in the metronome is adjusted individually. When, due to the influence of temperature or supply voltage, the frequency of the master oscillator changes, it is necessary to adjust the frequency F of each pace again. The task is greatly simplified if, on the basis of a single master oscillator, by dividing its frequency F0 by a certain counting factor, we obtain the frequency of any rate (similar to how it is done in devices [2]). Then, by correctly compensating for the drift of the frequency F0, it is possible to correctly adjust the frequency of not one, but all musical tempos at once.

Calculations show that it is most convenient to tune the master oscillator to the frequency of the "re" note of the 7th octave (theoretical value F0 = 18794,545 Hz). Then, dividing the frequency F0 by 8, we get the note "re" of the 4th octave, by 16 - "re" of the 3rd octave, by 32 - "re" of the 2nd octave, by 64 - "re" of the 1st octave . Finally, if F0 is divided by 8 using an 256-bit binary counter, we will generate rectangular pulses with a frequency of 73,4 Hz, which corresponds to the "D" note of the large octave.

Next, you will need to use a frequency divider that provides a variable two-digit counting factor (frequency division) K2. For example, if you set K2 = 98, then the total division factor K0 is easy to calculate: K0 = K1 K2 = - 256 98 - 25088, where K1 = 256 is the counting factor of the first (preliminary) counter. In this case, at the output of the second frequency divider, pulses with a frequency Fact of about 0,75 Hz (18794,5 Hz: 25088) and corresponding to the slowest Largo tempo are formed. When K2 = 21, then K0 = 256 21 = 5376, or Ffact = = 3,5 Hz - this is the fastest Prestissimo tempo. Other rates will be obtained by taking K2 equal to 85, 73, 63, 54, etc. (see Table 1). The table shows that the relative error in the formation of the frequency of different rates does not exceed 2%. In practice, such a small error is quite acceptable, since the frequency "distance" between adjacent rates is approximately 15%.

A diagram of a metronome built according to this principle is shown in Fig. 1. On logic elements DD1.1, DD1.2, resistors R1, R2 and capacitor C1, a master oscillator is assembled, which is tuned to the frequency of the "re" note of the 7th octave. In the first frequency divider (binary counters DD2.1, DD2.2), it gradually decreases. At the outputs of the counters, the note "re" of the corresponding octaves is formed (Fig. 1). Pulses from the last output (frequency 73,4 Hz) are fed to the input of the second frequency divider, made on counters DD3, DD4 and elements DD1.3, DD1.4, DD5.1. The remaining output signals of the counters DD2.1 and DD2.2 are applied to the contacts of the switch SA2.

(click to enlarge)

Suppose the slider of this switch is moved to the upper position according to the diagram; to the base of the amplifying transistor VT1, connected according to the emitter follower circuit with load resistors R5 and R6, pulses are supplied with a frequency of the "re" note of the 4th octave. When it is set to the second position from the top - the "re" notes of the 3rd octave, etc. If it is set to the lowest (fifth) position, this is the normal operating mode, in which pulses from the sound-forming part are sent to the base of the transistor VT1 metronome built on elements DD5.2 - DD5.4, resistors R3, R4, R7 and capacitors C2, C5.

The second (tunable) frequency divider is made according to the scheme described in [3, Fig.18]. The necessary account coefficient is set using the SA1 switch, which has 11 positions (according to the number of musical tempos). For example, if the engine is set to the lowest position, then the input 2 of the DD5.1 ​​element is connected to the output 2 (pin 4) of the counter DD4, which sets the number "20"; at the same time, input 1 of element DD5.1 ​​is connected to output 1 of counter DD3 (pin 2), which sets the number "1". Thus, the total score coefficient is 21, which corresponds to the Prestissimo tempo. If the slide switch SA1 is moved to the uppermost position, the inputs of the element DD5.1 ​​will be connected to the outputs 9 DD4 (pin 11) and 8 DD3 (pin 9), i.e. the numbers "90" and "8" are given, realizing the coefficient scores K2 = 98 (Largo pace). The correctness of setting other frequency division coefficients K2 can be easily seen from Fig. 1 and Table. 1. It is important that for any coefficient K2, a short pulse with a duration of 1.4 ms is formed at the output of the DD6,8 element. At a frequency of 3,5 Hz (Prestissimo tempo), the pulse repetition period is 286 ms, at a slow Largo tempo (0,75 Hz) - 1333 ms.

As soon as the mentioned pulse ends again, the previously discharged capacitor C2 turns out to be connected by its left (according to the diagram) plate to the case. The voltage level at the inputs of the DD5.2 element will become low, and at its output - high, allowing the operation of the sound generator on the elements DD5.3 and DD5.4. After some time, depending on the resistance of the variable resistor R4, the capacitor C2 will be charged (through resistors R3 and R4) so ​​much that the high level at the output of the DD5.2 element will change to low again, so the sound generator will stop. In other words, the sound generator here works for a short time, immediately after the end of the 6,8 ms pulse. When the pulse once again arises again, the capacitor C2 again quickly discharges. Discharging occurs through the internal diodes of the DD5.2 element: their cathode is connected to the power supply of the microcircuit, and the anode is connected to the corresponding input of the element. For more details, see [4, fig. 6]). How to set the duration of a sound pulse in order to achieve a “click” rather than a clearly distinguishable tone is described in detail in [1].

The resistance of the resistor R7 is selected so that the HA1 piezoceramic emitter operates at the main resonance frequency - according to [5], for the ZP-1 emitter, this is slightly more than 2 kHz. The blocking capacitor C3 serves to eliminate high-frequency voltage ripples in the power circuit, and C4 - low-frequency ones. The protective diode VD1 prevents the supply of reverse polarity voltage to the device. An output signal of 6 V can be removed from resistor R6 through capacitor C0,25, which allows you to connect a metronome to the input of sound-amplifying equipment (for example, through a mixer) if its volume is insufficient. Since the resistance R6 is small, the shielding requirements of the connecting wires can be significantly reduced.

In the pauses between individual "clicks" the metronome consumes almost no electricity, and during the "click" the current consumption increases to about 3...4 mA. It is clear that the greater the duration of the sound pulse (at a frequency of about 2 kHz, it should be at least 15 ms) and the higher the musical tempo will be the greater the energy consumption. So, at the Prestissimo tempo, the metronome consumes an average of 0,15 ... 0,2 mA, while at the Largo tempo it consumes only 0,03 ... battery 0,045D-7.

To adjust all the musical tempos of the metronome at the same time, it is enough to switch the SA2 switch to one of four tuning positions corresponding to the note "pe1", "pe2", "pe3" or "pe4". The position of the switch SA1 does not matter. Taking on any musical instrument with the correct tuning - piano, accordion or button accordion - exactly the same note, resistor R1 sets the frequency of the master oscillator, at which there are no beats of sounds. When this is achieved, the metronome setting will be as shown in Table 1. 4. Note that the note "pe3" will sound the loudest; the volume of the remaining notes, starting with "pe1" and up to "peXNUMX", will decrease as the octave number decreases.

In operating mode, the metronome reproduces single-tone sound shocks - "clicks". If it is necessary to reproduce both ordinary (ordinary) beats and accented (the strongest), you will have to introduce an additional node into the metronome, the scheme of which is shown in [1], fig. 2. For this, firstly, the following components are excluded: logic elements DD5.2 - DD5.4, transistor VT1, resistors R3 - R7, capacitors C2, C5, C6, emitter HA1. Secondly, instead of the capacitor C2, the lower output of the node is connected to the output of the metronome element DD1.4, which is designated "To pin 1 DD1". Thirdly, the on-off switch SA1 of the node is replaced by a five-position metronome switch SA2: the output of the element DD2.4 is connected to its lower fixed contact, and the moving contact is connected to the base of the transistor VT1 of the additional node. Both parts of the device are fed through a common diode VD1. The work of a metronome that reproduces "accents" and "ordinaries" is described in detail in [1].

But adjusting the metronome and periodically monitoring the correctness of its “building” is still not very convenient. Is it possible to avoid these procedures? It turns out it's quite possible. On fig. 2 shows a different part of the metronome. Instead of the excluded logical elements 001.1, DD1.2 and counters DD2.1, DD2.2 (see Fig. 1), a "clock" chip K176IE5 (DD2) was used, included according to the typical circuit in [6, Fig. 9]. The stability of the "tuning" of the metronome is achieved by stabilizing the frequency F0 = 32 Hz using a miniature "clock" quartz resonator ZQ768. At output 1 of the K9IE176 microcircuit (pin 5), rectangular pulses with a frequency of 1 Hz are formed. Roughly, the frequency is selected by capacitor C64, exactly - C1.

Pulses with a frequency of 64 Hz are fed to the input of a tunable divider assembled on two K561IE8 microcircuits (DD3 and DD4). The only difference is that the way the outputs of these microcircuits are routed to the SA1 switch is somewhat changed. Since the frequency of 64 Hz differs markedly from the frequency of 73,4 Hz of the previous version of the metronome, other values ​​of K2 and K1 = 512 are required (see Table 2). The table shows that the error in the formation of rates in this version of the metronome is less than in the previous one. Long-term frequency stability is much higher here. Note that instead of a short pulse with a duration of about 6,8 ms, a pulse with a duration of approximately 7,8 ms is formed. Both values ​​are equal to half the repetition period of the pulses applied to the input of the second frequency divider. Otherwise, the operation of this metronome is no different from the previous one.

Since it is no longer necessary to periodically control the frequency F0 of the master oscillator, switch SA2 is excluded from the circuit, and the base of transistor VT1 is connected to the output of element DD5.4 (notations in Fig. 1).

Since in this version of the metronome two elements DD1.1 and DD1.2 were released, it is advisable to assemble the final node of a push-pull bridge amplifier on them (excluding the transistor VT1, resistors R5 and R6, capacitor C6 and emitter HA1 - Fig. 1), operating in an economical switching mode (Fig. 3).

The amplifier works as follows. While there is no "click", at the input of the amplifier connected to pin 11 of the DD5 chip, there is a prohibitive low level, so the output of the DD1.1 element is high. Capacitor C8 is discharged through resistor R9. It only takes 15ms to discharge it. Because of this, the output of the DD1.2 element is also high, as a result of which all transistors VT1-VT4 are closed and the current does not flow through the variable resistor R10.

When a "click" appears at the input of the amplifier, which is a packet of rectangular pulses, the capacitor C8 is quickly charged through the diode VD2 and the resistor R8. Charging takes about 0,15ms. It remains charged as long as there are "click" pulses at the input of the amplifier. Therefore, the signals at the output of the elements DD1.1 and DD1.2 are out of phase during the sound transmission, which is necessary for the correct operation of the bridge amplifier [2]. Through the variable resistor R10 - the metronome volume control - an alternating current flows, periodically changing not only its magnitude, but also its direction, and the emitter HA1 reproduces this sound frequency.

But as soon as the next "click" ends, the capacitor is discharged so much that a high level appears both at the output of the element DD1.1 and DD1.2. In the future, the cycle of operation of the metronome amplifier is repeated.

The volume of a metronome with such an amplifier increases significantly, but the average current consumption also increases. For example, at the Largo tempo, the metronome consumes less than 1 mA on average, while at the Prestissimo tempo it consumes about 3 mA. But during the "click" and a little later, the current consumed is approximately 30 mA, so it is hardly advisable to power such a metronome from the "Krona" battery. It is better to use 5 ... 9 elements 334 or 337, the same number of batteries D-0,55 or 2 ... 3 batteries 3336. It is possible to somewhat reduce power consumption by reducing the resistance of the resistor R9. Then the time during which transistors VT1 and VT4 are constantly open after the "click" is reduced. The low-power part of the device (microcircuit) is fed from the same source through the VD1 diode.

The resonance frequency of the SP-1 emitter, according to [7], is 3...4 kHz. This means that the resistance of the resistor R7 will have to be reduced by 1,5 ... 2 times, thereby tuning the sound generator to the resonance of a particular emitter. In addition, it may be necessary to increase the capacitance of the capacitor C2 to about 0,15 microfarads, or to increase the resistance of the resistors R3 and R4 to 30 and 300 kOhm, respectively.

Literature

1. Bannikov V. Musical metronome. - Radio, 1996, No. 3, p. 52-55.
2. Bannikov V. Three-tone musical signaling devices. - Radio, 1996, No. 1, p. 46-48; No. 2, p. 45-47.
3. Alekseev S. The use of K561 series microcircuits. - Radio, 1986, No. 12, p. 42-46.
4. Alekseev S. Shapers and generators based on microcircuits of the CMOS structure. - Radio, 1985, No. 8, p. 31-35.
5. Alexandrov I. The use of sound emitter ZP-1. - Radio, 1985, No. 12, p. 54.
6. Alekseev S. The use of K176 series microcircuits. - Radio, 1984, No. 4, p. 25-28.
7. Nechaev I. Security devices with emitter SP-1. - Radio, 1986, No. 3, p. 42, 43.

Author: V.Bannikov, Moscow

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