Infrared remote control circuit principle design and analysis - circuit diagram reading every day (298)

LMSP33A-298

SMD aluminum electrolytic capacitor

The infrared remote control transmitting circuit uses infrared light emitting diodes to emit modulated infrared light waves; the infrared receiving circuit is composed of infrared receiving diodes, triodes or silicon photo cells, which convert infrared light emitted by the infrared emitter into corresponding electric signals, and then send them Set the amplifier. Remote control technology, also known as remote control technology, refers to the remote control of controlled targets, and is widely used in industrial control, aerospace and home appliances. Infrared remote control is a wireless, non-contact control technology with strong anti-interference ability, reliable information transmission, low power consumption, low cost, easy implementation, etc. It is widely used by many electronic devices, especially household appliances, and more and more More applications in computer systems.

The spectrum is outside the red light, and the wavelength is 0.76 to 1.5 μm, which is longer than the wavelength of the red light. Such light is called infrared light. Infrared remote control is a control system that transmits information by using infrared rays. The infrared remote control has the advantages of anti-interference, simple circuit, easy encoding and decoding, low power consumption and low cost. Currently, almost all video and audio devices support such control. the way.

Infrared remote control system structure Infrared remote control system is mainly divided into three parts: modulation, transmission and reception, as shown in Figure 1:

Figure 1 infrared remote control system

When the infrared remote control transmits data, the modulation method is adopted, that is, the data is “ANDed” with the carrier of a certain frequency, which can improve the transmission efficiency and reduce the power consumption of the power supply. The modulation carrier frequency is generally between 30khz and 60khz. Most use a 38kHz, square wave with a duty cycle of 1/3, as shown in Figure 2, which is determined by the 455kHz crystal used by the transmitter. At the transmitting end, the crystal is divided by an integer. The division factor is generally 12, so 455 kHz ÷ 12 ≈ 37.9 kHz ≈ 38 kHz.

Figure 2 carrier waveform

The launch system currently has a variety of chips that can be used for infrared transmission, and different types of codes can be issued depending on the choice. Since the transmitting system is generally powered by a battery, this requires that the power consumption of the chip is very low. Most of the chips are designed to be in a sleep state, and work when a button is pressed. This can reduce the power consumption of the chip. The physical impact resistance can not be selected from ordinary quartz crystals. Generally, ceramic resonators are used. The accuracy of ceramic resonators is not as high as that of quartz crystals, but usually a little error is negligible. Infrared light is emitted through an infrared light emitting diode (LED). The internal material of the infrared light emitting diode is different from that of a normal light emitting diode. When a certain voltage is applied to both ends of the infrared light emitting diode, it emits infrared light instead of visible light.

Figure 3a Simple drive circuit

Figure 3b Shooting output drive circuit

As shown in Fig. 3a and Fig. 3b, the driving circuit of the LED, Fig. 3a is the simplest circuit. When selecting components, pay attention to the switching speed of the triode, and also consider the forward current and reverse leakage current of the LED, generally flowing through the LED. The maximum forward current is 100mA, and the larger the current, the greater the intensity of the transmitted waveform. The circuit of Figure 3a has a flaw. When the battery voltage drops, the current flowing through the LED will decrease, the intensity of the transmitted waveform will decrease, and the remote control distance will become smaller. The emitter output circuit shown in Figure 3b can solve this problem. The two diodes clamp the base voltage of the three-stage tube to about 1.2V, so the emitter voltage of the three-stage tube is fixed at about 0.6V, and the emitter current IE is basically not According to IE≈IC, the current flowing through the LED is also basically unchanged, thus ensuring a certain remote distance when the battery voltage is lowered.

Infrared remote control switch circuit works

Figure 4 infrared remote control switch circuit diagram

The power circuit is composed of a power switch S, a step-down capacitor C1, a resistor R1, a Zener diode VS, a rectifier diode VD, and a filter capacitor C2. The remote control receiving circuit is composed of an infrared receiving head special component ICl and a resistor R2 and a capacitor C3. The counter circuit is composed of a serial counter integrated circuit IC2, a resistor R3, and a capacitor C4. The control execution circuit is composed of resistors R4, R5, a transistor V, and a crystal mesh tube VT.

An infrared remote controller used in home appliances such as television sets transmits about 10 sets of remote control code pulses per second, and there is a certain interval between each group of remote control code pulses. The infrared receiving head IC1 receives the infrared remote control signal transmitted by the remote controller and demodulates it, and outputs it. After R2 and C3 integration (filtering out the coding information in each group of pulses), it is enlarged from the 1 pin of the IC2 as the lC2. Count pulses (about 10 pulses per second). After 1C2 receives 8 pulses (about 0·8s), its 6 pin becomes low level or high level, which makes V and VT turn on or off, and the working power of the load (powered device) is turned on or disconnect.

Component selection

Rl-R5 uses "/4W carbon film resistor or metal film resistor."

C1 selects polyester capacitors or CBB capacitors with a withstand voltage of 400V or higher; C2-C4 selects aluminum electrolytic capacitors with a withstand voltage of 16V.

VD selects 1N4007 silicon rectifier diode for use.

VS selects 1/2W, 6·2V silicon steady voltage diode.

V selects the Model 59015 or 58550, C8550 type silicon PNP transistor.

VT selects 3A, 400V double-question thyristor.

ICl selects the TV's miniature integrated package infrared receiver (adding a cover or adding a translucent filter when used), IC2 selects CD4024 type 7-bit binary serial counter integrated circuit.

Circuit debugging

After the circuit is installed, connect the voltage and load, and change the resistance of R5 so that the AC voltage between the T1 pole and the T2 pole of VT is less than 3V.

Edit Comment: This article briefly introduces the principle of infrared remote control circuit. Infrared remote control is the most widely used communication and remote control method. The infrared remote control device has been widely used because of its small size, low power consumption, strong function, and low cost.
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