Air movement indicator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Indicators, detectors

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The air movement indicator (IPV) is a device that can perform different functions:

• a signaling device for opening (slamming) a vent, window or door by a sharp gust of wind;
• draft signaling device;
• signaling device for exceeding the threshold air velocity in enclosed spaces;
• signaling device for the presence of draft in the ventilation pipe.

It is advisable to use IPV for remote control of air movement, so the sensor with the board and power source can be located in one room, and the LED indicator can be located somewhere else. For example, to control the absence of a draft in the children's room, the LED can be taken out to the parents' bedroom or to the kitchen. A loud scream or cry of a child also turns on the LED indicator, warning of an "abnormal" situation.

The device can be embedded in a badge to highlight the symbol depicted on it. At a disco or a youth "party", such an icon will effectively "wink" to the beat of the music.

IPV (Fig. 1) consists of a miniature microphone with a built-in amplifier, a comparator, a field-effect transistor current switch and a high-brightness LED emitter. Microphone BM1 operating mode sets the tuning resistor R3. The comparator is assembled on the elements R1...R3, DA1. The current key is made on the transistor VT1. A current-limiting resistor R1 is connected in series with the HL1 LED in the VT5 drain circuit. Resistor R4 sets the programmable operational amplifier DA1.

When the contacts of the toggle switch SA1 are closed, the battery voltage GB1 is supplied to the IPV, and the device enters the economical standby mode. The divider R1-R2 sets a reference voltage close to 0,5 Upit at the inverting input (pin 2) DA1. Resistor R3 and microphone BM1 form a second voltage divider, the signal from the midpoint of which is fed to the non-inverting input (pin 3) DA1. When air currents appear that cause noise in the microphone, voltage spikes of positive polarity appear on the upper output of the BM1 output. And if the amplitude of these surges exceeds the reference voltage level (0.5Upit), a voltage close to the supply voltage appears at the output (pin 6) of DA1. The op-amp is turned on without a feedback resistor, which achieves the maximum gain, and the op-amp itself performs the function of a comparator, i.e. it compares the voltage levels at the inputs and produces the result of the comparison in the form of low or high level pulses at the output.

If the voltage at the direct (non-inverting) input is greater. than on the inverting one, the output voltage of the op-amp tends to + Upit. And if the voltage at the direct input is less than at the inverting one, at the output of the op-amp - the potential of the common wire (in the case of a unipolar power supply). The maximum output voltage DA1 is approximately 1 V less than Upit. The transistor switch VT1 allows Uzi<20 V and does not require a current-limiting resistor in the gate circuit. During pulses of positive polarity, the drain-source junction VT1 opens, and the HL1 LED glows brightly. Resistor R5 limits the current flowing in the load to the nominal current of the LED HL1 (20 mA).

The IPV setting consists in setting the bias voltage (+1,2 ... 2 V) at pin 3 of DA1. A lower voltage corresponds to a lower sensitivity of the IPV. At a voltage less than +1,2 V, the sensitivity of the IPV drops sharply.

Assembled without errors and from serviceable elements, the device starts working immediately after setup. You can specify the value of the operating current through the HL1 LED by selecting R5. To do this, a milliammeter is connected to the drain circuit, the VT1 gate is temporarily disconnected from the DA1 output and connected to -Upit. The resistance R5 changes as follows. so that the current through HL1 does not exceed the maximum. When using unknown LEDs, you can use the rule: current up to 10 mA is acceptable for almost any type of LED. It should be noted that some super-bright LEDs have a higher operating voltage (307 ... 3 V) compared to "traditional * LEDs (AL4, etc.).

In the IPV, OMLT resistors are used, the tuning resistor R3 is SDR-38a. Toggle switch SA1 - MTS-102, especially miniature SMTS-102 or slide, for example, from an old calculator. Replacing DA1 (with autonomous power supply) with other op-amps, except for K140UD12, is not advisable. Transistor VT1 can be replaced by KP501, KP504 with any letter index. LED HL1 white color ARL-3214UWC (20cd. diameter 3 mm) is replaced, for example, by a super-bright green color 10G4DHCBB20 (4 chips in one package, 3,8 V. 80 mA) or, in extreme cases, low-power with increased brightness, for example , emerald TTL-500G3VC-2 (3.5 V, 20 mA) with built-in lens. Microphone BM1 - electret, can be replaced by a similar one, for example, a very miniature XF-18D (d=6 mm. h=3.8 mm).

IPV is placed on a printed circuit board made of one-sided foil fiberglass with dimensions of 34x12x1,5 mm. The drawing of the board is shown in Fig. 2, and the location of the elements is shown in Fig. 3.

The diameter of the holes on the printed circuit board for the microcircuit is 0,7 ... 0.8 mm. for other parts - 0,8 ... 1 mm, for connecting conductors - 1 ... 1.2 mm. The IPV board for size reduction does not have mounting holes and is installed in the case on friction. The pattern of the printed conductors can be transferred to copper foil by thermal transfer (1] or transferred through a carbon paper and circled with an acid-resistant permanent marker "Centropen 2846 CE PERMANENT", etc.), as well as a marker for signing computer CDs,

The IPV case can be homemade. Its dimensions are determined mainly by the size of the batteries used. The author's version of the IPV is placed in a rectangular plastic soap dish measuring 105x68x36 mm with a paper false-panel glued on it and protected with adhesive tape (Fig. 4), printed on a color printer. The IPV is powered by a 3R12G "flat" battery or 3-4 D-0.26D batteries (25 mm in diameter).

Depending on the purpose of the IPV. The BM1 microphone is installed inside the case or is brought out through the connector. Connecting wires are unshielded. up to 0,5 m long.

Literature

1. A. Oznobikhin. VHF receiver "1066-R". - Radiomir, 2007. No. 8, p.41.

Author: A. Oznobikhin, Irkutsk

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