SOS device. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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SOS device. 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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It happens that the elderly and sick people are left alone for a long time without supervision. At this time, a sharp deterioration in their well-being can occur, to the point that they are unable to dial an ambulance phone number, in general - to call someone for help.

The device proposed below, called "SOS" in connection with its purpose, can help patients who find themselves in an extreme situation.

The structure of the "SOS" device includes: an alarming non-sinking button, mounted in the patient's room so that he can effortlessly reach the button and press it once; functional units - a timer and an alarm signal generator with a loudspeaker output, mounted in a room where there are people who can quickly come to the aid of the patient on an alarm signal (the apartment of relatives or friends of the patient, landing).

The panic button is connected to the timer by a two-wire line. It is enough for the patient to press the panic button, as the timer will turn on the generator for a certain time (2 ... 4 minutes), and during this time the alarm signal will be played by the loudspeaker. The signal can be played repeatedly by repeatedly pressing the button.

Schematic diagram of "SOS" is shown in fig. one.

SOS device

The device is assembled on only three ICs (DD1 K561LE5, DD2 K176IE5, DD3 K561IE16). Elements DD1.1 and DD1.2 form an RS flip-flop, and DD1.3 and DD1.4 form an alarm signal generator.

When the alarm button SB1 is open, the output 3DD1.1 has a logic 1 (high voltage level). This signal, acting on the inputs R IC DD2 and DD3, sets their outputs respectively 15(5) and 26(6), 27(13), 28(12), logic 0 (low voltage level)

The signal with level 1 from the output 3 DD1.1 through the diode VD1 is supplied to the inputs 8, 9 DD1.3, preventing the generation of an alarm signal. At the same time, logic 11 is set at output 1.4 DD1, transistor VT1 is in cut-off mode and there is practically no current in its collector circuit. So when the SB 1 button is open, the current from the GB1 battery with a voltage of 9 V is consumed only to power the IC. Due to the insignificance of this current, there is no power switch for the device.

When the button SB 1 is pressed once, the RS-flip-flop switches to another state and 3 appears at the output 1.1 DD1 instead of 0, which is fed to the inputs of R counters. From this moment, the IC counters DD2 and DD3 begin to count the pulses arriving at them. At the same time, the alarm generator also starts to work.

The internal generator IC DD2 generates a pulse sequence with a frequency close to 16384 Hz. The generation frequency is determined by the parameters of the timing circuit C3R5: the capacitance of the capacitor C3 and the resistance of the resistor R5 are calculated and selected using the recommendations given in the article by L. Medinsky "Economic time relay" in Radio, 1988, No. 1, p. 40-43. At the specified frequency, positive pulses with a frequency of about 15 Hz appear at the output 5(2) of the counter DD1. Each pulse enters through the diode VD2 to input 8 DD1.3 and strobes an alarm signal.

Second pulses are counted by the counter DD3. As the output is used pin 27(13) counter DD3. With this inclusion, a positive pulse at the output 27 (13) appears 2 minutes after pressing the SB1 button. This means that the alarm signal will be reproduced by the electrodynamic head BA1 for 2 minutes. When using output 26(6) DD3, the signal will sound for only 1 minute, with 28(12) - 4 minutes. To facilitate such switching, additional contact pads are provided on the printed circuit board.

The positive pulse that appeared at the switched on output of the IC DD3 through the differentiating circuit C2R2 is fed to pin 6 of DD1.2 and returns the RS flip-flop to its original state, at which the counters and the alarm generator stop working.

A sketch of the printed circuit board of the device is shown in fig. 2.

SOS device

The device uses small capacitors, MLT-0,125 resistors. Loud sound is reproduced by dynamic drivers 0,1 - 0,5 W with voice coils with a resistance of more than 6-8 ohms. The volume is easily adjusted by changing the resistance of the resistor R6.

Author: A.Mikhalev, Yekaterinburg

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