Electronic bicycle bell. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic bicycle bell. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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To increase the safety of cycling, it is desirable to equip it with an audible signaling device - a "bell". The structure of an electronic call includes an AF generator, a power amplifier and a dynamic head or other acoustic emitter. Using an electronic call is much more convenient and faster than using a traditional mechanical one.

Additional functions can be assigned to this electronic device. For example, it can become an acoustic "beacon", periodically giving short beeps. This mode of operation will certainly be useful when hiking for mushrooms, in order not to lose the bike in the thicket of the forest.

The scheme of the device is shown in fig. one.

Electronic bicycle bell

The element DD1.1 assembled the first generator of rectangular pulses with variable duty cycle. The element DD1.2 made the second generator of rectangular pulses. Their repetition frequency is about 1 kHz, i.e. lies in the middle of the sound range. A buffer amplifier is assembled on the elements DD1.3, DD1.4, and on the transistor VT1 - a key, the load of which is the dynamic head BA1.

The device works as follows. In the initial state, the contacts of the switches SB1, SA1 are open, as shown in fig. 1, and the device does not consume current. In the "Signal" mode, the buttons SB1.1 and SB1.2 are closed and power is supplied to all elements. The diode VD1 is closed in this mode, so the first generator generates rectangular pulses with a duty cycle of about 2. Their repetition rate is determined by the capacitance of the capacitor C1 and the resistance of the resistor R2. It is a few hertz. When pin 3 of the DD1.1 element is low, the second generator does not work and the key is closed. When a high logic level appears on this pin, the second generator will start working and a sound signal will be heard in the BA1 head. Thus, in this mode, a signal is generated that sounds like "beep-beep-beep".

If you turn on switch SA1 ("Beacon" mode), then power will also be supplied to the device, but the first generator will generate pulses with a duty cycle of about 300 and a repetition period of 18 ... 20 s. This is due to the fact that the charging of the capacitor C1 occurs relatively quickly through the diode VD1 and the resistor R2 of low resistance. Discharging occurs through a resistor R1 with a large resistance, and therefore is carried out much more slowly. In this mode, the second generator turns on for a short time at long intervals, i.e. the device works as an acoustic "beacon".

The device is powered by a battery of batteries or galvanic cells with a total voltage of 3 ... 6 V. The blocking capacitor C3 is installed parallel to the battery before the switches, this is done so that after releasing the button SB1 or turning off the switch SA1, the sound signal immediately stops.

Most of the parts are placed on a printed circuit board (Fig. 2) made of one-sided foil fiberglass. The board, dynamic head and battery must be placed in a case of suitable dimensions, while it is desirable to install the SB1 button so that it is convenient to use it to give an audio signal, for example, near the steering wheel.

Electronic bicycle bell

The following parts can be used in the device: the K561TL1 chip is replaceable by K564TL1, but the board will have to be modified, the KD102B diode is replaced by KD10Z, KD521, KD522, all diodes can be with any letter indices, polar capacitors - K50 - 35 or similar, C2 - K10 - 17, fixed resistors - MLT, C2 - 33. The SB1 button is suitable for any small-sized two-position and two-way self-returning switch, the SA1 switch is also any small-sized one. For a dynamic head with a resistance of 50 ohms, the transistor VT1 can be, in addition to that indicated on the diagram, the KT315 series with indices B, E, as well as any of the KT3102, KT3117 series.

If you use a dynamic head with a resistance of 8 - 16 ohms, then the volume of the signal will increase noticeably, but the current consumed from the battery will also increase. In addition, it will be necessary to use transistors KT829A - KT829G, KT972A, KT972B or powerful key field-effect transistors IRLR2905 or similar, as well as increase the capacitance of capacitor C3 to 2200 uF. Of course, the battery must provide the required current up to about 0,2 A.

Establishment comes down to setting the operating modes of generators. The pitch of the sound signal, i.e. the frequency of the second generator, is set by selecting the resistor R3, for this it is necessary to temporarily short-circuit the capacitor C1 in order to obtain a continuous signal. Then, by pressing the SB1 button, by selecting the resistor R2, the most suitable mode of operation of the first generator is set. When the switch SA1 is on, by selecting the value of the resistor R1, the required period of the sound signal is set.

Author: I. Nechaev, Kursk

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