Light switch on "IR rays". Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / infrared technology

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The advantage of IR remote control (hereinafter referred to as remote control) has already been experienced by everyone. Remote control has invaded our daily lives and saves us time enough. But at the moment, unfortunately, not all electrical appliances are equipped with remote control. This also applies to light switches. True, our industry is currently producing such a switch, but it costs a lot of money, and it is very, very difficult to find it.

This article proposes a fairly simple circuit of such a switch. Unlike the industrial one, which includes one BIS, it is mainly assembled on discrete elements, which, of course, increases the dimensions, but, if necessary, can be easily repaired. But if you are chasing dimensions, then in this case you can use planar parts. This circuit also has a built-in transmitter (industrial ones do not), which saves you from having to carry the remote control with you all the time or look for it. It is enough to bring your hand to the switch at a distance of up to ten centimeters and it will work. Another advantage is that any remote control from any imported or domestic radio equipment is suitable for remote control.

Transmitter

Figure 1 shows a diagram of the emitter of short pulses [1]. This allows you to reduce the current consumed by the transmitter from the power source, which means extending the service life on one battery. On the elements DD1.1, DD1.2, a pulse generator is assembled, following with a frequency of 30 ... 35 Hz. Short, 13 ... 15 μs duration, pulses are formed by the differentiating circuit C2R3. Elements DD1.4-DD1.6 and a normally closed transistor VT1 form a pulse amplifier with an IR diode VD1 on the load.

(click to enlarge)

The dependence of the main parameters of such a generator on the supply voltage Upit is shown in the table.

Table 1

Here: Iimp is the amplitude of the current in the IR diode, Ipot is the current consumed by the generator from the power source (with the value of resistors R5 and R6 indicated on the diagram).

Any remote control from domestic or imported equipment (TV, VCR, music center) can also serve as a transmitter.

The printed circuit board is shown in Fig.3. It is proposed to make it from double-sided foil fiberglass with a thickness of 1,5 mm. The foil on the side of the parts (not shown in the figure) performs the function of a common (negative) wire of the power source. Areas 1,5–2 mm in diameter are etched around the holes for passing the leads of parts in the foil. The conclusions of the parts connected to the common wire are soldered directly to the foil of this side of the board. Transistor VT1 is attached to the board with an M3 screw, without any heat sink. The optical axis of the IR diode VD1 must be parallel to the board, and 5 mm apart from it.

Receiver (with built-in transmitter)

The receiver is assembled according to the classical scheme adopted in the Russian industry (in particular, in Rubin, Temp TVs, etc.) [1]. Its circuit is shown in Figure 2. IR radiation pulses fall on the IR photodiode VD1, are converted into electrical signals and amplified by transistors VT3, VT4, hard labor is connected according to a common emitter circuit. An emitter follower is assembled on the transistor VT2, matching the resistance of the dynamic load of the photodiode VD1 and the transistor VT1 with the input impedance of the amplifier stage on the transistor VT3. Diodes VD2, VD3 protect the pulse amplifier on the transistor VT4 from overloads. All receiver input amplifier stages are covered by deep current feedback. This provides a constant position of the operating point of the transistors regardless of the external illumination level - a kind of automatic gain control, which is especially important when the receiver is operated in rooms with artificial lighting or outdoors in bright daylight, when the level of extraneous IR radiation is very high.

Next, the signal passes through an active filter with a double T-shaped bridge, assembled on a VT5 transistor, resistors R12-R14 and capacitors C7-C9. Transistor VT5 must have a current transfer coefficient H21e = 30, otherwise the filter may start to be excited. The filter cleans the transmitter signal from AC mains interference emitted by electric lamps. The lamps create a modulated radiation flux with a frequency of 100 Hz and not only in the visible part of the spectrum, but also in the IR region. The filtered signal of the code message is formed on the transistor VT6. As a result, short pulses are obtained on its collector (if received from an external transmitter) or proportional with a frequency of 30 ... 35 Hz (if received from a built-in transmitter).

The pulses coming from the receiver are fed to the buffer element DD1.1, and from it to the rectifier circuit. The rectifier circuit VD4, R19, C12 works like this: When the output of the element is logical 0, then the VD4 diode is closed and the capacitor C12 is discharged. As soon as pulses appear at the output of the element, the capacitor begins to charge, but gradually (not from the first pulse), and the diode prevents it from discharging. Resistor R19 is chosen in such a way that the capacitor has time to charge up to a voltage equal to logic 1 with only 3 ... 6 pulses coming from the receiver. This is another protection against interference, short IR flashes (for example, from a camera flash, lightning, etc.). The discharge of the capacitor occurs through the resistor R19 and takes 1 ... 2 s in time. This prevents crushing and arbitrary switching on and off of the light. Next, an amplifier DD1.2, DD1.3 with capacitive feedback (C3) is installed to obtain sharp rectangular drops at its output (when turned on and off). These drops are fed to the input of the divider by 2 trigger assembled on the DD2 chip. Its non-inverted output is connected to an amplifier based on the VT10 transistor, which controls the VD11 thyristor, and the VT9 transistor. Inverted is applied to the transistor VT8. Both of these transistors (VT8, Vt9) serve to ignite the corresponding color on the VD6 LED when the light is turned on and off. It also performs the function of a "beacon" when the light is off. An RC circuit is connected to the input R of the divider trigger, which resets. It is needed so that if the voltage in the apartment is turned off, then after turning on the light does not accidentally light up.

The built-in transmitter is used to turn on the light without a remote control (when bringing your palm to the switch). It is assembled on elements DD1.4-DD1.6, R20-R23, C14, VT7, VD5. The built-in transmitter is a pulse generator with a repetition rate of 30 ... 35 Hz and an IR LED is connected to the load by hard labor. The IR LED is installed next to the IR photodiode and must be directed in the same direction with it, and they must be separated by an opaque partition. Resistor R20 is selected in such a way that the actuation distance, when the palm is raised, is 50 ... 200 mm. In the built-in transmitter, you can use an IR diode of the AL147A type or any other. (For example, I used an IR diode from an old drive, but the resistor R20=68 Ohm).

The power supply is assembled according to the classical scheme on KREN9B and the output voltage is 9V. It includes DA1, C15-C18, VS1, T1. Capacitor C19 serves to protect the device from power surges.

The load on the diagram is shown with an incandescent lamp.

The printed circuit board of the receiver (Fig. 4) is made of one-sided foil fiberglass with a size of 100X52 mm and a thickness of 1,5 mm. All parts, with the exception of the diode VD1, VD5, VD8, are installed as usual, the same diodes are installed from the mounting side. Diode bridge VS1 is assembled and discrete rectifier diodes are often used in imported technology. The diode bridge (VD8-VD11) is assembled on diodes of the KD213 series (others are indicated in the diagram), the diodes are soldered one above the other (column), this method is used to save space.

Literature:

1. Radio No. 7, 1996, pp. 42-44. "IR sensor in the burglar alarm."

Author: Rusin Alexander Sergeevich, Moscow; Publication: N. Bolshakov, rf.atnn.ru

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