Transmitter in infrared communication line. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / infrared technology

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Its schematic diagram is shown in fig. 55. Here DD1.1, DD1.2, R3, ZQ1 is a clock generator excited at a frequency of a quartz resonator fp = 32768 Hz. DD3 - a counter, at output 11 (pin 15) of which a 16-Hz square wave is formed (f11 = fp / 2 ^ 11), and at output 14 (pin 3) - 2-Hz (f14 = fp / 2 ^ 14) . Elements DD2.1-DD2.4 form a switch, at the output of which (output DD2.4) a 2-Hz or 16-Hz square wave appears, depending on the voltage level at input 5 of the DD2.1 * element.

From the front of the meander, the differentiating circuit R5C3 and the pulse amplifier DD1.4-DD1.6 form a current pulse of duration t and in the base of a normally closed transistor VT1@10 µs (ti@R5 C3). The current arising in the collector circuit of the transistor VT1 excites the IR diode BI1 and a short IR flash is emitted into space.

So, the IR transmitter always emits something - either rare, 2-Hz pulses, if there are no grounds for alarm, or frequent, 16-Hz pulses - alarming.

Rice. 55. Transmitter IR communication line (click to enlarge)

Rice. 56. Transmitter circuit board

On fig. 56 shows the printed circuit board of the transmitter, which is made of double-sided foil fiberglass with a thickness of 1,5 mm. The foil on the side of the parts is used only as a neutral wire - "ground"; fragments of one or another configuration are etched in it in places where conductors are passed. The place of soldering to the null foil of the "grounded" output of the resistor, capacitor, etc. is shown by a blackened square; connecting to it the output of a microcircuit or a wire jumper - a square with a light dot in the center.

A hole for an IR diode is drilled in the center of the board, its leads are soldered to the corresponding extensions on the printed conductors overlaid.

All resistors of the IR transmitter are of the MLT-0,125 type. Capacitors: C1, C2, C5 - KM-6 (outputs in one direction); C4 - K50-6; C6 - TOWA or other, with a diameter of not more than 10 mm; C3 - KM-5 (outputs in different directions).

Commercially available IR diodes are designed to operate in remote control devices for household radios and usually have a fairly wide - up to 30 ... 400 - radiation lobe. To increase the "range" of such an emitter, it is necessary to introduce a condenser lens into it. So, as shown in fig. 57. Here: 1 - printed circuit board of the transmitter; 2 - IR diode; 3 - transmitter housing (high-impact polystyrene 2 ... 2,5 mm thick); 4 - clip of a standard 5x hour magnifier (there should be a "x5" icon on it); 5 - its lens.

Fig.57. Housing with concentrator lens

The magnifying glass is glued to the front wall of the case (glue - pieces of polystyrene dissolved in solvent 647 or RS-2; the case itself is also glued with it), in which a hole with a diameter of 30 ... 35 mm is made. At the distance indicated on the drawing between the base of the magnifier and the printed circuit board, the IR diode is at the focus of its lens, its radiation is compressed into a narrow beam, and the illumination of the photodetector window at the other end of the IR communication line increases many times.

The most important parameter of the IR transmitter, as well as any element of security equipment, is its power consumption in standby mode. Table 11 shows the dependence of the current Iconsumed by it on the voltage of the power supply Upit. In the alarm transmission mode, Iload increases by about 10%.

Low overall power consumption allows you to enter a backup power supply directly into the body of the IR transmitter without increasing its dimensions. This can be, for example, a 6-volt battery type 11A (Ж10,3x16 mm, capacity 33 mAh) or 476A (Ж13x25 mm, capacity 105 mAh). The dependence of the current in the IR diode Iimp on the supply voltage shown in Table 11 makes it possible to judge the power of the IR flashes emitted by the transmitter, and, accordingly, its "range".

Table 11

Upit,B	Ipot, mA	Iimp, A
4,2	0,20	0,36
5,0	0,40	0,46
6.0	0,77	0,64
7,0	1,30	0,82
8,0	1,90	0,97
9,0	2,70	1.23
10,0	3,60	1,38

When placing the transmitter, you need to remember the very narrow diagram of its radiation. The attachment point should allow accurate aiming of the transmitter and its rigid fixation in the best position. You can use, for example, a swivel head from a camera or movie camera, mounting it on a wall, window frame, etc. Or make this knot in the form of two brass patches connected by annealed copper

Rice. 58. Transmitter mount

wire with a diameter of 2 ... 2,5 mm (Fig. 58). One of the spots is fixed with screws to the side wall of the emitter (the thread is in the wall), the other is screwed to the support. The wire is bent so that the emitter takes the desired position. To avoid significant vibrations, it should be as short as possible.

Tests have shown that with Upit=6 V the transmitter is able to provide communication at a distance of r@70 meters (with photodetector described below). But this is not the limit. The dependence of r on Iimp ceteris paribus has the form: r@to·ЦIimp, where k is a coefficient that takes into account "Other conditions". Thus, at Upit \u10d XNUMX V r@100 m. The current in the IR diode can also be increased due to the resistance of the resistor R7: Iimp \u4d [Upit-7] / R7 (Iimp - in amperes, Upit - in volts, R7 - in ohms). But this should be done with caution: in any combination of Upit and R3, the current amplitude in the IR diode should not exceed the maximum allowable (see Appendix XNUMX).

A significant increase in the brightness of the IR flash can be obtained by rebuilding the "high-current" part of the pulse amplifier as shown in Fig. 59 (printed circuit board - in Fig. 60, a, b). In this case, the current in the pulse Iimp = 10 A can be achieved - permissible for an IR diode of the AL123A type. Resistor R4 is a self-made, measured on a digital ohmmeter or calculated (see Appendix 8) piece of nichrome, constantan or manganin wire.

Rice. 59. Emitter head with IR diode AL123A

Rice. 60. Printed circuit board of the head of a powerful IR emitter

The amplitude and shape of the current that excites the IR diode can be monitored with an oscilloscope by connecting it to resistor R4.

The radiating head can be made as a separate unit in "all-weather" design. All other elements of the IR emitter can enter the electronic part of the security system as its fragment, connected to the IR head only by a thin three-wire cable.

Rice. 61. IR receiver (click to enlarge)

*) Highlighted in the figure by a dash-dotted line is an example of a security system sensor that generates the desired signal at its output.

Publication: cxem.net

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