A simple electric bell. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple electric bell. 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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The proposed musical call plays several melodies. Can be used as an alarm clock. The "heart" of the call can be a MONTANA alarm clock. The clock must be removed from the case, unscrew the screws that fasten the board to the indicator, solder the leads with thin conductors according to Fig. 1 and fix the board back in place.

Simple electric bell

These pins connect the clock to the circuit shown in Fig.2.

Simple electric bell

The work of the scheme and the purpose of the elements. The audio frequency amplifier is made on the elements R2, VT1, VT2. Trimmer resistance R1 sets the volume of the sound. Capacitor C1 prevents power consumption by the amplifier in standby mode. The diode assembly VDl, VD2 is necessary for the simultaneous supply of a positive pulse to pins 1 (DATE) and 2 (ALTM). The fact is that you can forcibly turn on the melody in the clock by simultaneously pressing the two DATE and ALTM buttons. The clock does not block the playback of a melody. Therefore, with frequent pressing of the call button, the melodies will change randomly.

In order to prevent this from happening, elements C3, VD3, R3, VD4, C4 are introduced into the circuit. When you press the bell button (contacts K1, K2), a positive pulse enters through the capacitor C3 and the diode assembly VD1, VD2 to pins 1, 2 hours. After the start of playing the melody, the sound frequency enters the capacitor C3 and charges it. A charged capacitor does not pass a positive pulse from contact K1. Thus, the call will not respond to pressing the K1, K2 buttons while the melody is playing.

After the end of the melody, the bit circuit VD3, R3 discharges the capacitor C3, preparing it to receive the next signal. If the bell button (K1, K2) is not released, then the capacitor C3 will not be discharged and the call will go into standby mode. There will be no continuous playback of the melody. Capacitors C2, C5 protect the call from false alarms, which can be triggered by impulse noise induced in the wire connected to contact K1.

Power supply of the bell is independent (two R-20 batteries). The clock is powered by 1,5 V, and the amplifier is 3 V.

The maximum energy consumption occurs during the playback of a melody. In standby mode, power is consumed only to keep the clock running. In practice, in this mode, the life of the batteries is determined by their own self-discharge. Buttons SBl (ALTM), SB2 (DATE), SB3 (MODE) are used to control the clock. In order for the call not to work automatically when the alarm time coincides with the current time, you must turn on the alarm (the symbol will disappear) and switch the clock to the stopwatch mode. Melodies will turn on, but the alarm clock will not.

In MONTANA brand watches, the number of melodies and the melodies themselves are different. This makes it possible to change the melodies by replacing the clock. The call is assembled in the housing of the subscriber loudspeaker, the clock and the button are displayed on the front panel.

Author: S.M.Usenko, Chernihiv region

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