Humidity is controlled by a cell phone. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Humidity control devices usually use threshold stages of varying complexity that respond to a decrease in resistance between the electrodes. The proposed version of the moisture meter is simpler, but it also controls the resistance between the electrodes and emits an audible signal when it decreases.

This device can be used, for example, to signal the filling of a container, such as a bathtub, with water, signaling the dampness of the plaster (if the tenant fills the floor above), giving an alarm in case of water appearing on the floor before it reaches the neighbors downstairs apartment. In addition, it can be used as a self-powered buzzer that is triggered when a circuit is closed.

The design is assembled on the basis of a children's toy "cell phone". It contains a specialized integrated circuit (IC) that outputs one of the musical phrases recorded in it through the dynamic head when one of the buttons on the toy's keyboard is pressed.

All keyboard buttons (S1 - SN in Fig. 1) are connected in parallel and connected between the plus of the power source and pin 1 of the IC (IC in a frameless design, pin numbers are assigned conditionally).

The triggering of the threshold device at the input of the IC occurs when the resistance between the contacts of any button is about 500 kOhm. The simplest way to implement the task is to turn on the humidity sensor in parallel with the buttons, however, in this case, when the IC is triggered, only one recorded phrase is issued, which may not be enough. To issue the next phrase, it is necessary to open and close the sensor circuit again. A similar principle is used in the device, but instead of opening the circuit, reverse polarity voltage is applied in series with the sensor.

The sensor leads are connected to the sockets of connector X1. When the sensor circuit is open (the monitored "object" is dry), the potential of output 1 is close to the potential of the negative power bus (it is "pulled up" by the built-in IC resistor). When the sensor circuit closes or the resistance between its terminals becomes less than 500 kOhm, terminal 1 is connected to the positive power bus through the sensor, resistors R1, R2 and the secondary winding of the transformer T1. In this case, the output potential relative to the positive bus decreases, and at a certain value, the IC threshold device is triggered. A sound signal appears in the dynamic head BA1. The head current flows through the primary winding of the transformer, as a result of which an alternating voltage appears in the secondary winding. It is rectified by the diode VD2. The rectified voltage is smoothed by capacitor C3 and fed through the sensor to pin 1 of the IC. The output potential rises, which is equivalent to opening the sensor circuit.

At the end of the issuance of the musical phrase by the IC, the signal at its output disappears, the capacitor C3 is discharged to resistors R1 and R2. The potential of output 1 decreases, which causes the threshold device to reactivate and produce the next piece of music. Further, the described process is periodically repeated until the sensor circuit breaks.

The transformer is necessary to increase the amplitude of the signal at the rectifier input in order to ensure a clear operation of the device with a partially discharged battery, which is not always achieved by directly removing the signal from the IC output. Diode VD1 protects the input of the IC from the reverse voltage at an increased output voltage of the rectifier, capacitors C1 and C2 increase the noise immunity of the device when using a long cable connecting it to the sensor.

The transformer is made on a K7x4x4 ferrite ring. Winding I contains 20 turns of wire PELSHO 0,3, winding 11-140 turns of wire PEV 0,12. ConnectorX1 - block MGK1-1 or any other small-sized, other parts - any suitable size. Capacitors C1 and C2 are located as close as possible to the IC, the rest - in the free space of the case. The installation view is shown in fig. 2.

Separately, we should dwell on the design of the sensor that controls the dryness of the plaster and gives a signal about the leakage of water from the neighbors from above. It can be made from paper laminated with aluminum foil used to wrap cigarettes inside a pack.

To do this, the specified paper is first perforated, for example, using a hole punch or a blunt needle on a sewing machine. After that, the strips of paper are glued with a paper base to each other with a blotting or filter pad between them. For this purpose, it is necessary to choose glue that is easy to swell when damp. Starch paste brewed in a concentrated solution of table salt is best suited. When dampened, salt increases the conductivity between the aluminum plates.

To connect the sensor to the device, the connecting wires must be soldered to the aluminum plates (Fig. 3) using an aluminum flux. The worst results are obtained by gluing flexible conductors with adhesive tape. If there are several sensors, they are placed in places of alleged leaks and connected in parallel.

The device does not require special adjustment. If there are long pauses between musical phrases, you should replace the resistor R1 with another, less resistance.

Author: D.Volkov, Shakhty, Rostov region

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