Night attack alarm. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electronics in medicine

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Diabetes mellitus, which is one of the most common "diseases of civilization", is dangerous for its surprises, among which is hypoglycemia, i.e. a sharp drop in blood sugar levels. If hypoglycemia, which occurs quickly and suddenly, is not detected in time and emergency measures are not taken, a hypoglycemic crisis can end tragically [1].

In France, to detect the precursors of hypoglycemia at night, when the patient is sleeping, a miniature device has been created, consisting of a sensor and a pair of electrodes placed in a watch-like bracelet and worn on the patient's hand. The bracelet is connected by wires to an electronic device that emits an audible signal that wakes the patient up when cold sweat appears, a mandatory sign of impending hypoglycemia [2].

The main disadvantage of such a signaling device is the presence of connecting wires, they create great inconvenience during sleep and can break at any time.

The simplest wireless signaling device (Fig. 1) consists of an electronic key on a transistor VT1, a sensor (sensors E1 and E2 - two metal plates) and a piezoceramic sound emitter BF1 (with a built-in sound generator). Sensors E1 and E2, 10x10 mm in size, are made of metal foil and are placed (glued) on the inside of the watch strap at a distance of 1 mm from each other.

Fig.1. The simplest wireless alarm

If the skin is dry, the resistance of the sensor is high, the transistor VT1 is closed, and the supply voltage is not supplied to the sound emitter BF1. In this mode, the current consumed by the signaling device is a few microamperes, so there is no power switch in the device. When the skin is wet, the resistance of the sensor decreases sharply, the transistor opens, and the supply voltage is supplied through it to the sound emitter. The emerging sound wakes the patient.

The device uses MLT-0,125 resistors, a sound emitter of the NSM1201X type (HPA24AX, GS1201S), a KT361 transistor (KT104, KT209) with any letter index, the power source is two D-0,1 type batteries connected in series with a voltage of 1,2 V.

If a radio amateur does not have a sound emitter with a built-in indicator at his disposal, you can use the electronic "stuffing" of a musical card instead. The postcard sound generator in most cases is a frameless microcircuit with 4 or 6 pins. Two of them are the power supply of the microcircuit, they are not difficult to determine, since they are connected to the power supply. The other two are connected to a miniature sound-emitting head. If the microcircuit has six pins, the remaining two are usually used to connect the second same head. The power outputs of the microcircuit are connected (observing the polarity) instead of the sound emitter BF1.

The second version of the signaling device (Fig. 2) is designed for remote monitoring of the patient's condition (especially young children and the elderly) and can be used both at home and in the hospital.

Fig.2. Signaling device for remote control (click to enlarge)

The device consists of an electronic key (transistor VT4), a sensor (sensors E1 and E2), a low-power transmitter (transistor VT3) and a low-frequency generator (transistors VT1 and VT2). The small transmitter [3] operates in the FM band. Its radius of action is 35 ... 40 m. An antenna WA7 is connected through the capacitor C1, which is a piece of mounting wire d1 ... 2 mm and about 100 mm long. The wire is wrapped around the patient's wrist. A low-frequency generator based on transistors VT1 and VT2 [4] is a symmetrical multivibrator that generates pulses with a frequency of about 200 Hz. Instead of a low-frequency generator, as in the first version, you can use the electronic "stuffing" of a musical card.

After assembling the signaling device and checking the installation, they proceed to the adjustment. First, the operation of the electronic key is checked by connecting the sensors E1 and E2 to each other. The voltage between the collector of the transistor VT4 and the "-" terminal of the power supply should be about 2 V. To check the operation of the low-frequency generator, headphones are connected to the right (according to the circuit) output of the capacitor C3 and make sure that there is an audible signal. The adjustment of the transmitter comes down to setting (focusing on the scale of an industrial radio receiver) a frequency equal to 87,9 MHz (specially allocated for the operation of radio microphones), by selecting the capacitance of capacitor C5. The joint operation of the transmitter with the signaling device is checked by closing the sensors of the sensor E1 and E2. The receiver should hear a tone.

All parts of the signaling device are located on the watch strap, on the inside of which the sensor sensors are located. From above, to exclude mechanical damage, the signaling device is covered with polyethylene or soft plastic.

The design of the above signaling device can be reduced by several times if surface mount parts (SMD) are used. Since in this case coil L1 is the largest in size, a flat coil can be used to reduce the dimensions, the calculation of which is carried out according to the method described in [5]. The device uses MLT-0,125 resistors; small ceramic capacitors type KM. Instead of the transistors VT1 and VT2 indicated in the diagram, transistors KT315 with any letter index can be used, VT3 - KT368A, KT355A. The RF generator coil contains 5 turns of PEV-1 wire d0,5 mm on a d5 mm frame.

Sources of

1. Gruzina E.A. and other Care of patients with endocrine diseases. - Kyiv: Health, 1982, p.16.
2. Inventor and innovator, 1980, N10.C.24.
3. Kutsko I. Radiotelephone. - Radio, 2001, N6, C57.
4. The best designs of the 26th exhibition of radio amateurs. - M.: DOSAAF, 1975, p.182.
5. Yankin Yu. Calculation and production of flat coils. - Radio, 1976, N11, p.40.

Author: V.Yalansky

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