IR repeater. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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IR repeater. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / infrared technology

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IR - remote control is currently used in everyday life very widely. Other schemes suggest using an infrared sensor in the alarm system. However, such systems require a line of sight between the IR transmitter and the receiver, and the range of the optical communication line does not exceed 5...8 meters. How to significantly increase this distance is described in this article.

The principle of information relaying to increase the transmission range has long been widely used in radio engineering. At the same time, it does not matter in what form the information is presented and what are the methods of its transmission. Each of them has its advantages and disadvantages and is selected depending on the goals, technical and economic feasibility.

As noted in the preamble of this article, infrared radiation is now very widely used in remote control and monitoring systems. All remote control systems for mass household equipment (TVs, indoor air conditioning systems, security systems) have IR control. This is due to the possibility of secrecy of information transmission, the absence of interference from these systems to other equipment and the noise immunity of the systems themselves. Many types of IR photodetectors have been mass-produced for a long time, and their prices are constantly decreasing. So, the TSOP1738 type photodetector and similar ones are now widely used. The photodetector requires a +5V source to power it. There are photodetectors rated for 3,3V, but they are less common.

The scheme of the IR "Extension" is shown in the figure.

(click to enlarge)

The signal from the photodetector through the resistor R1 is fed to the base of the transistor T2. The collector of this transistor is connected to a load resistor R3 and the input R of timer IC1 type NE555. If the photodiode of the integrated photodetector TSOP1738 is irradiated with IR radiation from an external source, then zero potential appears at the output of the photodetector (pin 2). Accordingly, the transistor T2 is turned off, and the potential of the power supply of the +12 V circuit through the resistor R3 is fed to the input R of the timer IC1. The timer is authorized to operate. In this circuit, it is included as a generator. The generation frequency is determined mainly by the values of C3, R4, P1. By adjusting the tuning resistance P1, you can select a frequency in the range of 36 ... 48 kHz. As a rule, most TSOP1738 photodetectors have the highest sensitivity at 38 kHz.

The output of IC1 from pin 3 is fed through resistor R5 to the base of transistor T1. Its emitter load is a pair of IR emitting LEDs LD2, LD3 and an indication LED LD1. Resistors R7 and R8 are ballast and limit the current of the LEDs.

The supply voltage of the photodetector +5 V is removed from the zener diode D1. Capacitor C2 is a blocking capacitor in the power supply circuit of the photodetector.

In [1], it is recommended to use a capacitor C3 with a small TKE. Of the domestic types, it is desirable to use KSO-1.

By adjusting the tuning resistance P1, you can achieve the highest sensitivity of the receiving part of the device, which will also provide the greatest communication range in the IR range.

Author: E.L. Yakovlev, Uzhgorod, Ukraine

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